OT antenna question

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OT antenna question

Victor Rosenthal 4X6GP
I'm having a problem which has me stumped. I'm going to describe my
complete antenna and feed system because something in it is misbehaving
and I don't know what!

My system works on all bands from 40 to 10 (or it should).

The antenna is a full-size 20m rotary dipole. It is all aluminum tubing,
no traps or stubs. Just a dipole. I am feeding it with about 30 feet of
"true ladder line," which is open wire line made of #16 insulated wire
spaced about 3-1/4" with black PVC spacers every 18" or so, except near
the antenna and the rotor where I've added extra ones so that the
spacing doesn't change when the antenna rotates.

The line comes into the shack and is connected to a static drain, which
is a box with two 10-megohm high voltage resistors to ground and a
couple of spark gaps. Then a piece of 450-ohm window line about 3 feet
long connects it to a pair of large air variable capacitors in series
with each leg which knock out some of the reactance on 40m to make it
possible to tune more easily. Then a very short piece of window line
connects to a big 5kW DX Engineering 4:1 balun, spec'ed for tuner
service, and finally via a piece of RG-213 18" long, to a T-network tuner.

My K3 drives a TL922 amp and I have an SWR meter in line.

Now here is my problem: it works OK on all bands except 40 meters. On
40, it tunes up fine with low power, but when I run more than a couple
of hundred watts, after perhaps 10 seconds of key-down, the SWR starts
to climb. I have watched it go to 4:1 before I stop sending for fear of
destroying something.

The SWR rises both on the meter in the tuner and the extra one I have in
line.

Classic symptoms of something heating up. But what?

- The tuner components are all cold.
- The coax to the balun and its connectors are cold.
- The balun itself is just barely perceptibly warmer (I have to touch
the core to tell).
- The window line, the static drain resistors, the air capacitors and
all the connections in the shack are cold.

I know the SWR is astronomical on 40 meters, so currents and voltages
are high. But nothing in the shack seems to be heating up. Any more
ideas of where to look?

--
73,
Vic, 4X6GP/K2VCO
Rehovot, Israel
http://www.qsl.net/k2vco/
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Re: OT antenna question

daleputnam
It would be very interesting to do that test... key for 10 sec.. if it is possible - on an early morning, that has frost or snow on the spacers...Look for the one that becomes dry or drippy.

Have a great day,
 
 
--...   ...--
Dale - WC7S in Wy
 
 


> To: [hidden email]
> From: [hidden email]
> Date: Tue, 12 Jan 2016 23:24:12 +0200
> Subject: [Elecraft] OT antenna question
>
> I'm having a problem which has me stumped. I'm going to describe my
> complete antenna and feed system because something in it is misbehaving
> and I don't know what!
>
> My system works on all bands from 40 to 10 (or it should).
>
> The antenna is a full-size 20m rotary dipole. It is all aluminum tubing,
> no traps or stubs. Just a dipole. I am feeding it with about 30 feet of
> "true ladder line," which is open wire line made of #16 insulated wire
> spaced about 3-1/4" with black PVC spacers every 18" or so, except near
> the antenna and the rotor where I've added extra ones so that the
> spacing doesn't change when the antenna rotates.
>
> The line comes into the shack and is connected to a static drain, which
> is a box with two 10-megohm high voltage resistors to ground and a
> couple of spark gaps. Then a piece of 450-ohm window line about 3 feet
> long connects it to a pair of large air variable capacitors in series
> with each leg which knock out some of the reactance on 40m to make it
> possible to tune more easily. Then a very short piece of window line
> connects to a big 5kW DX Engineering 4:1 balun, spec'ed for tuner
> service, and finally via a piece of RG-213 18" long, to a T-network tuner.
>
> My K3 drives a TL922 amp and I have an SWR meter in line.
>
> Now here is my problem: it works OK on all bands except 40 meters. On
> 40, it tunes up fine with low power, but when I run more than a couple
> of hundred watts, after perhaps 10 seconds of key-down, the SWR starts
> to climb. I have watched it go to 4:1 before I stop sending for fear of
> destroying something.
>
> The SWR rises both on the meter in the tuner and the extra one I have in
> line.
>
> Classic symptoms of something heating up. But what?
>
> - The tuner components are all cold.
> - The coax to the balun and its connectors are cold.
> - The balun itself is just barely perceptibly warmer (I have to touch
> the core to tell).
> - The window line, the static drain resistors, the air capacitors and
> all the connections in the shack are cold.
>
> I know the SWR is astronomical on 40 meters, so currents and voltages
> are high. But nothing in the shack seems to be heating up. Any more
> ideas of where to look?
>
> --
> 73,
> Vic, 4X6GP/K2VCO
> Rehovot, Israel
> http://www.qsl.net/k2vco/
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]
     
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Re: OT antenna question

Guy Olinger K2AV
In reply to this post by Victor Rosenthal 4X6GP
Hi Vic,

Your story does suggest trouble at very high current points. Just a list of
things below I've heard or seen to stir up a new idea or two. No opinion on
which if any makes any sense in your situation.

---------

Insect nests in tubular spacers on open wire.

Spacers have carbon tracks.

Material inside the balun housing is much hotter than touchable material.

Stranded wire in open wire has been waterlogged, corroded and the remaining
conductor material at a current max along the line is heating up.

Wire inside insulation is nearly all broken, or is broken, and contact is
miscellaneous and highly resistive.

Insulation on the wire is significantly compromised by ultra violet or
critter nibbling, letting in water to the stranded conductor. Advice, has
been to use bare solid #12 copper or larger for open wire that is carrying
large standing waves, to handle the current maximums.

Check heat all around the entire core. I have burned up some number of
cores before I understood the materials and engineering. On one all the
damage was on a spot that comprised only 15 degrees of the circumference.

Electrical connections in aluminum elements made of telescoping tubing go
highly resistive as water is boiled out of the joints.

Connections made of dissimilar metals/materials go bad and become more
resistive as water is boiled out of the joint.

Tuner rotary switches going bad.

The rolling contact on on a variable coil losing its tension (numerous ways
for this to happen depending on construction), contact is very small and
becomes worse as it heats up. Fixed by repairing mechanism for maintaining
contact.

Parted conductors at conductor joints due to metal erosion at the contact
point.

--------

Your troubles would have me taking down the dipole, rebuilding it with all
mating surfaces wire-brushed and reassembled with clear silicone dielectric
grease, completely new hardware likewise treated, with all balanced
conductors replaced new, using bare solid #12 outdoors, and brand new runs
indoors. Old wire to recycling.

Hope this has kicked off a new idea for you.  73 and good luck.  Guy K2AV

On Tue, Jan 12, 2016 at 4:24 PM, Vic Rosenthal 4X6GP/K2VCO <
[hidden email]> wrote:

> I'm having a problem which has me stumped. I'm going to describe my
> complete antenna and feed system because something in it is misbehaving and
> I don't know what!
>
> My system works on all bands from 40 to 10 (or it should).
>
> The antenna is a full-size 20m rotary dipole. It is all aluminum tubing,
> no traps or stubs. Just a dipole. I am feeding it with about 30 feet of
> "true ladder line," which is open wire line made of #16 insulated wire
> spaced about 3-1/4" with black PVC spacers every 18" or so, except near the
> antenna and the rotor where I've added extra ones so that the spacing
> doesn't change when the antenna rotates.
>
> The line comes into the shack and is connected to a static drain, which is
> a box with two 10-megohm high voltage resistors to ground and a couple of
> spark gaps. Then a piece of 450-ohm window line about 3 feet long connects
> it to a pair of large air variable capacitors in series with each leg which
> knock out some of the reactance on 40m to make it possible to tune more
> easily. Then a very short piece of window line connects to a big 5kW DX
> Engineering 4:1 balun, spec'ed for tuner service, and finally via a piece
> of RG-213 18" long, to a T-network tuner.
>
> My K3 drives a TL922 amp and I have an SWR meter in line.
>
> Now here is my problem: it works OK on all bands except 40 meters. On 40,
> it tunes up fine with low power, but when I run more than a couple of
> hundred watts, after perhaps 10 seconds of key-down, the SWR starts to
> climb. I have watched it go to 4:1 before I stop sending for fear of
> destroying something.
>
> The SWR rises both on the meter in the tuner and the extra one I have in
> line.
>
> Classic symptoms of something heating up. But what?
>
> - The tuner components are all cold.
> - The coax to the balun and its connectors are cold.
> - The balun itself is just barely perceptibly warmer (I have to touch the
> core to tell).
> - The window line, the static drain resistors, the air capacitors and all
> the connections in the shack are cold.
>
> I know the SWR is astronomical on 40 meters, so currents and voltages are
> high. But nothing in the shack seems to be heating up. Any more ideas of
> where to look?
>
> --
> 73,
> Vic, 4X6GP/K2VCO
> Rehovot, Israel
> http://www.qsl.net/k2vco/
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]
>
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Re: OT antenna question

Elecraft mailing list
In addition to the comments already, PVC material is notorious for breaking down under high voltage RF.  Avoid at all costs.  Use Pol-ethylene "rain for rent" tubing.  Works well in high Voltage RF.

Mel, K6KBE


      From: Guy Olinger K2AV <[hidden email]>
 To: Vic Rosenthal 4X6GP/K2VCO <[hidden email]>
Cc: Elecraft Reflector <[hidden email]>
 Sent: Tuesday, January 12, 2016 3:27 PM
 Subject: Re: [Elecraft] OT antenna question
   
Hi Vic,

Your story does suggest trouble at very high current points. Just a list of
things below I've heard or seen to stir up a new idea or two. No opinion on
which if any makes any sense in your situation.

---------

Insect nests in tubular spacers on open wire.

Spacers have carbon tracks.

Material inside the balun housing is much hotter than touchable material.

Stranded wire in open wire has been waterlogged, corroded and the remaining
conductor material at a current max along the line is heating up.

Wire inside insulation is nearly all broken, or is broken, and contact is
miscellaneous and highly resistive.

Insulation on the wire is significantly compromised by ultra violet or
critter nibbling, letting in water to the stranded conductor. Advice, has
been to use bare solid #12 copper or larger for open wire that is carrying
large standing waves, to handle the current maximums.

Check heat all around the entire core. I have burned up some number of
cores before I understood the materials and engineering. On one all the
damage was on a spot that comprised only 15 degrees of the circumference.

Electrical connections in aluminum elements made of telescoping tubing go
highly resistive as water is boiled out of the joints.

Connections made of dissimilar metals/materials go bad and become more
resistive as water is boiled out of the joint.

Tuner rotary switches going bad.

The rolling contact on on a variable coil losing its tension (numerous ways
for this to happen depending on construction), contact is very small and
becomes worse as it heats up. Fixed by repairing mechanism for maintaining
contact.

Parted conductors at conductor joints due to metal erosion at the contact
point.

--------

Your troubles would have me taking down the dipole, rebuilding it with all
mating surfaces wire-brushed and reassembled with clear silicone dielectric
grease, completely new hardware likewise treated, with all balanced
conductors replaced new, using bare solid #12 outdoors, and brand new runs
indoors. Old wire to recycling.

Hope this has kicked off a new idea for you.  73 and good luck.  Guy K2AV

On Tue, Jan 12, 2016 at 4:24 PM, Vic Rosenthal 4X6GP/K2VCO <
[hidden email]> wrote:

> I'm having a problem which has me stumped. I'm going to describe my
> complete antenna and feed system because something in it is misbehaving and
> I don't know what!
>
> My system works on all bands from 40 to 10 (or it should).
>
> The antenna is a full-size 20m rotary dipole. It is all aluminum tubing,
> no traps or stubs. Just a dipole. I am feeding it with about 30 feet of
> "true ladder line," which is open wire line made of #16 insulated wire
> spaced about 3-1/4" with black PVC spacers every 18" or so, except near the
> antenna and the rotor where I've added extra ones so that the spacing
> doesn't change when the antenna rotates.
>
> The line comes into the shack and is connected to a static drain, which is
> a box with two 10-megohm high voltage resistors to ground and a couple of
> spark gaps. Then a piece of 450-ohm window line about 3 feet long connects
> it to a pair of large air variable capacitors in series with each leg which
> knock out some of the reactance on 40m to make it possible to tune more
> easily. Then a very short piece of window line connects to a big 5kW DX
> Engineering 4:1 balun, spec'ed for tuner service, and finally via a piece
> of RG-213 18" long, to a T-network tuner.
>
> My K3 drives a TL922 amp and I have an SWR meter in line.
>
> Now here is my problem: it works OK on all bands except 40 meters. On 40,
> it tunes up fine with low power, but when I run more than a couple of
> hundred watts, after perhaps 10 seconds of key-down, the SWR starts to
> climb. I have watched it go to 4:1 before I stop sending for fear of
> destroying something.
>
> The SWR rises both on the meter in the tuner and the extra one I have in
> line.
>
> Classic symptoms of something heating up. But what?
>
> - The tuner components are all cold.
> - The coax to the balun and its connectors are cold.
> - The balun itself is just barely perceptibly warmer (I have to touch the
> core to tell).
> - The window line, the static drain resistors, the air capacitors and all
> the connections in the shack are cold.
>
> I know the SWR is astronomical on 40 meters, so currents and voltages are
> high. But nothing in the shack seems to be heating up. Any more ideas of
> where to look?
>
> --
> 73,
> Vic, 4X6GP/K2VCO
> Rehovot, Israel
> http://www.qsl.net/k2vco/
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]
>
______________________________________________________________
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Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

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Message delivered to [hidden email]


 
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Re: OT antenna question

David Olean
In reply to this post by Victor Rosenthal 4X6GP
Hello Vic,
It sure behaves like a ferrite core heating up!  After that, you must check
everything up at the antenna. One thing you might try is to see how long it
takes for the VSWR to drop to normal after a long key down session. A long
time indicates something with some mass to it that holds heat. If it takes
awhile to cool down, I would not suspect hot wires or an overheated joint.

Dave K1WHS


----- Original Message -----
From: "Vic Rosenthal 4X6GP/K2VCO" <[hidden email]>
To: "Elecraft Reflector" <[hidden email]>
Sent: Tuesday, January 12, 2016 9:24 PM
Subject: [Elecraft] OT antenna question


> I'm having a problem which has me stumped. I'm going to describe my
> complete antenna and feed system because something in it is misbehaving
> and I don't know what!
>
> My system works on all bands from 40 to 10 (or it should).
>
> The antenna is a full-size 20m rotary dipole. It is all aluminum tubing,
> no traps or stubs. Just a dipole. I am feeding it with about 30 feet of
> "true ladder line," which is open wire line made of #16 insulated wire
> spaced about 3-1/4" with black PVC spacers every 18" or so, except near
> the antenna and the rotor where I've added extra ones so that the spacing
> doesn't change when the antenna rotates.
>
> The line comes into the shack and is connected to a static drain, which is
> a box with two 10-megohm high voltage resistors to ground and a couple of
> spark gaps. Then a piece of 450-ohm window line about 3 feet long connects
> it to a pair of large air variable capacitors in series with each leg
> which knock out some of the reactance on 40m to make it possible to tune
> more easily. Then a very short piece of window line connects to a big 5kW
> DX Engineering 4:1 balun, spec'ed for tuner service, and finally via a
> piece of RG-213 18" long, to a T-network tuner.
>
> My K3 drives a TL922 amp and I have an SWR meter in line.
>
> Now here is my problem: it works OK on all bands except 40 meters. On 40,
> it tunes up fine with low power, but when I run more than a couple of
> hundred watts, after perhaps 10 seconds of key-down, the SWR starts to
> climb. I have watched it go to 4:1 before I stop sending for fear of
> destroying something.
>
> The SWR rises both on the meter in the tuner and the extra one I have in
> line.
>
> Classic symptoms of something heating up. But what?
>
> - The tuner components are all cold.
> - The coax to the balun and its connectors are cold.
> - The balun itself is just barely perceptibly warmer (I have to touch the
> core to tell).
> - The window line, the static drain resistors, the air capacitors and all
> the connections in the shack are cold.
>
> I know the SWR is astronomical on 40 meters, so currents and voltages are
> high. But nothing in the shack seems to be heating up. Any more ideas of
> where to look?
>
> --
> 73,
> Vic, 4X6GP/K2VCO
> Rehovot, Israel
> http://www.qsl.net/k2vco/
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]

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Re: OT antenna question

Bob McGraw - K4TAX
In reply to this post by Guy Olinger K2AV
If your tuner uses disk ceramic caps, as many do, these can be heating thus not being able to handle the RF current.  They heat and cool and change value which in turn changes tuning.  

Replacing them with suitable RF current rated units is the solution.

Bob, K4TAX


Sent from my iPhone

> On Jan 12, 2016, at 5:27 PM, Guy Olinger K2AV <[hidden email]> wrote:
>
> Hi Vic,
>
> Your story does suggest trouble at very high current points. Just a list of
> things below I've heard or seen to stir up a new idea or two. No opinion on
> which if any makes any sense in your situation.
>
> ---------
>
> Insect nests in tubular spacers on open wire.
>
> Spacers have carbon tracks.
>
> Material inside the balun housing is much hotter than touchable material.
>
> Stranded wire in open wire has been waterlogged, corroded and the remaining
> conductor material at a current max along the line is heating up.
>
> Wire inside insulation is nearly all broken, or is broken, and contact is
> miscellaneous and highly resistive.
>
> Insulation on the wire is significantly compromised by ultra violet or
> critter nibbling, letting in water to the stranded conductor. Advice, has
> been to use bare solid #12 copper or larger for open wire that is carrying
> large standing waves, to handle the current maximums.
>
> Check heat all around the entire core. I have burned up some number of
> cores before I understood the materials and engineering. On one all the
> damage was on a spot that comprised only 15 degrees of the circumference.
>
> Electrical connections in aluminum elements made of telescoping tubing go
> highly resistive as water is boiled out of the joints.
>
> Connections made of dissimilar metals/materials go bad and become more
> resistive as water is boiled out of the joint.
>
> Tuner rotary switches going bad.
>
> The rolling contact on on a variable coil losing its tension (numerous ways
> for this to happen depending on construction), contact is very small and
> becomes worse as it heats up. Fixed by repairing mechanism for maintaining
> contact.
>
> Parted conductors at conductor joints due to metal erosion at the contact
> point.
>
> --------
>
> Your troubles would have me taking down the dipole, rebuilding it with all
> mating surfaces wire-brushed and reassembled with clear silicone dielectric
> grease, completely new hardware likewise treated, with all balanced
> conductors replaced new, using bare solid #12 outdoors, and brand new runs
> indoors. Old wire to recycling.
>
> Hope this has kicked off a new idea for you.  73 and good luck.  Guy K2AV
>
> On Tue, Jan 12, 2016 at 4:24 PM, Vic Rosenthal 4X6GP/K2VCO <
> [hidden email]> wrote:
>
>> I'm having a problem which has me stumped. I'm going to describe my
>> complete antenna and feed system because something in it is misbehaving and
>> I don't know what!
>>
>> My system works on all bands from 40 to 10 (or it should).
>>
>> The antenna is a full-size 20m rotary dipole. It is all aluminum tubing,
>> no traps or stubs. Just a dipole. I am feeding it with about 30 feet of
>> "true ladder line," which is open wire line made of #16 insulated wire
>> spaced about 3-1/4" with black PVC spacers every 18" or so, except near the
>> antenna and the rotor where I've added extra ones so that the spacing
>> doesn't change when the antenna rotates.
>>
>> The line comes into the shack and is connected to a static drain, which is
>> a box with two 10-megohm high voltage resistors to ground and a couple of
>> spark gaps. Then a piece of 450-ohm window line about 3 feet long connects
>> it to a pair of large air variable capacitors in series with each leg which
>> knock out some of the reactance on 40m to make it possible to tune more
>> easily. Then a very short piece of window line connects to a big 5kW DX
>> Engineering 4:1 balun, spec'ed for tuner service, and finally via a piece
>> of RG-213 18" long, to a T-network tuner.
>>
>> My K3 drives a TL922 amp and I have an SWR meter in line.
>>
>> Now here is my problem: it works OK on all bands except 40 meters. On 40,
>> it tunes up fine with low power, but when I run more than a couple of
>> hundred watts, after perhaps 10 seconds of key-down, the SWR starts to
>> climb. I have watched it go to 4:1 before I stop sending for fear of
>> destroying something.
>>
>> The SWR rises both on the meter in the tuner and the extra one I have in
>> line.
>>
>> Classic symptoms of something heating up. But what?
>>
>> - The tuner components are all cold.
>> - The coax to the balun and its connectors are cold.
>> - The balun itself is just barely perceptibly warmer (I have to touch the
>> core to tell).
>> - The window line, the static drain resistors, the air capacitors and all
>> the connections in the shack are cold.
>>
>> I know the SWR is astronomical on 40 meters, so currents and voltages are
>> high. But nothing in the shack seems to be heating up. Any more ideas of
>> where to look?
>>
>> --
>> 73,
>> Vic, 4X6GP/K2VCO
>> Rehovot, Israel
>> http://www.qsl.net/k2vco/
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>> Message delivered to [hidden email]
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]
>

______________________________________________________________
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Re: OT antenna question

Joe Subich, W4TV-4

On 1/12/2016 10:57 PM, Bob McGraw K4TAX wrote:
 > If your tuner uses disk ceramic caps, as many do, these can be
 > heating thus not being able to handle the RF current.  They heat
 > and cool and change value which in turn changes tuning.

Particularly if you are using a 4:1 balun!  On 40 meters the impedance
of the half size antenna is *very low*.  The 4:1 balun will further
decrease the impedance seen by the tuner causing it to work at its
absolute worst efficiency (highest circulating current).

At the very least see if you can extend the dipole to 44', then get
some Smith Chart software and see if you can find a compromise
feedline length that provides a reasonable impedance on all bands,
and finally replace the 4:1 balun with a high quality 1:1 current
balun.

By extending the dipole you should be able to find a compromise
feedline length that will provide a 100 - 300 Ohm impedance on
all bands - something the tuner will be much happier to with and
be far more efficient than working at best than 10 Ohms as it
probably is doing on 40 meters.

73,

   ... Joe, W4TV


On 1/12/2016 10:57 PM, Bob McGraw K4TAX wrote:

> If your tuner uses disk ceramic caps, as many do, these can be heating thus not being able to handle the RF current.  They heat and cool and change value which in turn changes tuning.
>
> Replacing them with suitable RF current rated units is the solution.
>
> Bob, K4TAX
>
>
> Sent from my iPhone
>
>> On Jan 12, 2016, at 5:27 PM, Guy Olinger K2AV <[hidden email]> wrote:
>>
>> Hi Vic,
>>
>> Your story does suggest trouble at very high current points. Just a list of
>> things below I've heard or seen to stir up a new idea or two. No opinion on
>> which if any makes any sense in your situation.
>>
>> ---------
>>
>> Insect nests in tubular spacers on open wire.
>>
>> Spacers have carbon tracks.
>>
>> Material inside the balun housing is much hotter than touchable material.
>>
>> Stranded wire in open wire has been waterlogged, corroded and the remaining
>> conductor material at a current max along the line is heating up.
>>
>> Wire inside insulation is nearly all broken, or is broken, and contact is
>> miscellaneous and highly resistive.
>>
>> Insulation on the wire is significantly compromised by ultra violet or
>> critter nibbling, letting in water to the stranded conductor. Advice, has
>> been to use bare solid #12 copper or larger for open wire that is carrying
>> large standing waves, to handle the current maximums.
>>
>> Check heat all around the entire core. I have burned up some number of
>> cores before I understood the materials and engineering. On one all the
>> damage was on a spot that comprised only 15 degrees of the circumference.
>>
>> Electrical connections in aluminum elements made of telescoping tubing go
>> highly resistive as water is boiled out of the joints.
>>
>> Connections made of dissimilar metals/materials go bad and become more
>> resistive as water is boiled out of the joint.
>>
>> Tuner rotary switches going bad.
>>
>> The rolling contact on on a variable coil losing its tension (numerous ways
>> for this to happen depending on construction), contact is very small and
>> becomes worse as it heats up. Fixed by repairing mechanism for maintaining
>> contact.
>>
>> Parted conductors at conductor joints due to metal erosion at the contact
>> point.
>>
>> --------
>>
>> Your troubles would have me taking down the dipole, rebuilding it with all
>> mating surfaces wire-brushed and reassembled with clear silicone dielectric
>> grease, completely new hardware likewise treated, with all balanced
>> conductors replaced new, using bare solid #12 outdoors, and brand new runs
>> indoors. Old wire to recycling.
>>
>> Hope this has kicked off a new idea for you.  73 and good luck.  Guy K2AV
>>
>> On Tue, Jan 12, 2016 at 4:24 PM, Vic Rosenthal 4X6GP/K2VCO <
>> [hidden email]> wrote:
>>
>>> I'm having a problem which has me stumped. I'm going to describe my
>>> complete antenna and feed system because something in it is misbehaving and
>>> I don't know what!
>>>
>>> My system works on all bands from 40 to 10 (or it should).
>>>
>>> The antenna is a full-size 20m rotary dipole. It is all aluminum tubing,
>>> no traps or stubs. Just a dipole. I am feeding it with about 30 feet of
>>> "true ladder line," which is open wire line made of #16 insulated wire
>>> spaced about 3-1/4" with black PVC spacers every 18" or so, except near the
>>> antenna and the rotor where I've added extra ones so that the spacing
>>> doesn't change when the antenna rotates.
>>>
>>> The line comes into the shack and is connected to a static drain, which is
>>> a box with two 10-megohm high voltage resistors to ground and a couple of
>>> spark gaps. Then a piece of 450-ohm window line about 3 feet long connects
>>> it to a pair of large air variable capacitors in series with each leg which
>>> knock out some of the reactance on 40m to make it possible to tune more
>>> easily. Then a very short piece of window line connects to a big 5kW DX
>>> Engineering 4:1 balun, spec'ed for tuner service, and finally via a piece
>>> of RG-213 18" long, to a T-network tuner.
>>>
>>> My K3 drives a TL922 amp and I have an SWR meter in line.
>>>
>>> Now here is my problem: it works OK on all bands except 40 meters. On 40,
>>> it tunes up fine with low power, but when I run more than a couple of
>>> hundred watts, after perhaps 10 seconds of key-down, the SWR starts to
>>> climb. I have watched it go to 4:1 before I stop sending for fear of
>>> destroying something.
>>>
>>> The SWR rises both on the meter in the tuner and the extra one I have in
>>> line.
>>>
>>> Classic symptoms of something heating up. But what?
>>>
>>> - The tuner components are all cold.
>>> - The coax to the balun and its connectors are cold.
>>> - The balun itself is just barely perceptibly warmer (I have to touch the
>>> core to tell).
>>> - The window line, the static drain resistors, the air capacitors and all
>>> the connections in the shack are cold.
>>>
>>> I know the SWR is astronomical on 40 meters, so currents and voltages are
>>> high. But nothing in the shack seems to be heating up. Any more ideas of
>>> where to look?
>>>
>>> --
>>> 73,
>>> Vic, 4X6GP/K2VCO
>>> Rehovot, Israel
>>> http://www.qsl.net/k2vco/
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Re: OT antenna question

Fred Townsend-2
Vic:
Sounds like you have some things to check. Joe and others have given good
advice. However I question your overall design. It sounds like you have a
number of mismatches in your system. For instance is the feed point
impedance of your 20M dipole >600 ohms at 40 meters?  I think not but that
would be your match for "true ladder line". Then you switch to 450 ohm
ladder line at the static box. Have you checked for fried spiders across the
spark gaps? Then you go through a couple of caps, value unknown into a 4:1
balun which would bring you down about a 100 ohms (neglecting the caps) at
the coax. Seems like you would be adding series inductance not capacitance
and then maybe a 6 or 8 to 1 balun. Overall it seems like you are tuning
your feedline not your antenna.   Also you do not say how much power you are
running but I am betting you are getting less than 10% to your antenna. If
you are running 500 watts that would leave 450 watts dissipated in your
feedline. Ouch! It could be your coax is melting.
Finally it sounds like you have multiple reflection points in your system
which isn't going to make your SWR meters very accurate. I recommend you try
simulating your transmission line in SPICE or some other simulation CAD
program and see what you really have.
73
Fred, AE6QL

-----Original Message-----
From: Elecraft [mailto:[hidden email]] On Behalf Of Joe
Subich, W4TV
Sent: Tuesday, January 12, 2016 8:59 PM
To: Elecraft Reflector
Cc: Vic Rosenthal 4X6GP/K2VCO
Subject: Re: [Elecraft] OT antenna question


On 1/12/2016 10:57 PM, Bob McGraw K4TAX wrote:
 > If your tuner uses disk ceramic caps, as many do, these can be  > heating
thus not being able to handle the RF current.  They heat  > and cool and
change value which in turn changes tuning.

Particularly if you are using a 4:1 balun!  On 40 meters the impedance of
the half size antenna is *very low*.  The 4:1 balun will further decrease
the impedance seen by the tuner causing it to work at its absolute worst
efficiency (highest circulating current).

At the very least see if you can extend the dipole to 44', then get some
Smith Chart software and see if you can find a compromise feedline length
that provides a reasonable impedance on all bands, and finally replace the
4:1 balun with a high quality 1:1 current balun.

By extending the dipole you should be able to find a compromise feedline
length that will provide a 100 - 300 Ohm impedance on all bands - something
the tuner will be much happier to with and be far more efficient than
working at best than 10 Ohms as it probably is doing on 40 meters.

73,

   ... Joe, W4TV


On 1/12/2016 10:57 PM, Bob McGraw K4TAX wrote:
> If your tuner uses disk ceramic caps, as many do, these can be heating
thus not being able to handle the RF current.  They heat and cool and change
value which in turn changes tuning.

>
> Replacing them with suitable RF current rated units is the solution.
>
> Bob, K4TAX
>
>
> Sent from my iPhone
>
>> On Jan 12, 2016, at 5:27 PM, Guy Olinger K2AV <[hidden email]> wrote:
>>
>> Hi Vic,
>>
>> Your story does suggest trouble at very high current points. Just a
>> list of things below I've heard or seen to stir up a new idea or two.
>> No opinion on which if any makes any sense in your situation.
>>
>> ---------
>>
>> Insect nests in tubular spacers on open wire.
>>
>> Spacers have carbon tracks.
>>
>> Material inside the balun housing is much hotter than touchable material.
>>
>> Stranded wire in open wire has been waterlogged, corroded and the
>> remaining conductor material at a current max along the line is heating
up.

>>
>> Wire inside insulation is nearly all broken, or is broken, and
>> contact is miscellaneous and highly resistive.
>>
>> Insulation on the wire is significantly compromised by ultra violet
>> or critter nibbling, letting in water to the stranded conductor.
>> Advice, has been to use bare solid #12 copper or larger for open wire
>> that is carrying large standing waves, to handle the current maximums.
>>
>> Check heat all around the entire core. I have burned up some number
>> of cores before I understood the materials and engineering. On one
>> all the damage was on a spot that comprised only 15 degrees of the
circumference.

>>
>> Electrical connections in aluminum elements made of telescoping
>> tubing go highly resistive as water is boiled out of the joints.
>>
>> Connections made of dissimilar metals/materials go bad and become
>> more resistive as water is boiled out of the joint.
>>
>> Tuner rotary switches going bad.
>>
>> The rolling contact on on a variable coil losing its tension
>> (numerous ways for this to happen depending on construction), contact
>> is very small and becomes worse as it heats up. Fixed by repairing
>> mechanism for maintaining contact.
>>
>> Parted conductors at conductor joints due to metal erosion at the
>> contact point.
>>
>> --------
>>
>> Your troubles would have me taking down the dipole, rebuilding it
>> with all mating surfaces wire-brushed and reassembled with clear
>> silicone dielectric grease, completely new hardware likewise treated,
>> with all balanced conductors replaced new, using bare solid #12
>> outdoors, and brand new runs indoors. Old wire to recycling.
>>
>> Hope this has kicked off a new idea for you.  73 and good luck.  Guy
>> K2AV
>>
>> On Tue, Jan 12, 2016 at 4:24 PM, Vic Rosenthal 4X6GP/K2VCO <
>> [hidden email]> wrote:
>>
>>> I'm having a problem which has me stumped. I'm going to describe my
>>> complete antenna and feed system because something in it is
>>> misbehaving and I don't know what!
>>>
>>> My system works on all bands from 40 to 10 (or it should).
>>>
>>> The antenna is a full-size 20m rotary dipole. It is all aluminum
>>> tubing, no traps or stubs. Just a dipole. I am feeding it with about
>>> 30 feet of "true ladder line," which is open wire line made of #16
>>> insulated wire spaced about 3-1/4" with black PVC spacers every 18"
>>> or so, except near the antenna and the rotor where I've added extra
>>> ones so that the spacing doesn't change when the antenna rotates.
>>>
>>> The line comes into the shack and is connected to a static drain,
>>> which is a box with two 10-megohm high voltage resistors to ground
>>> and a couple of spark gaps. Then a piece of 450-ohm window line
>>> about 3 feet long connects it to a pair of large air variable
>>> capacitors in series with each leg which knock out some of the
>>> reactance on 40m to make it possible to tune more easily. Then a
>>> very short piece of window line connects to a big 5kW DX Engineering
>>> 4:1 balun, spec'ed for tuner service, and finally via a piece of RG-213
18" long, to a T-network tuner.

>>>
>>> My K3 drives a TL922 amp and I have an SWR meter in line.
>>>
>>> Now here is my problem: it works OK on all bands except 40 meters.
>>> On 40, it tunes up fine with low power, but when I run more than a
>>> couple of hundred watts, after perhaps 10 seconds of key-down, the
>>> SWR starts to climb. I have watched it go to 4:1 before I stop
>>> sending for fear of destroying something.
>>>
>>> The SWR rises both on the meter in the tuner and the extra one I
>>> have in line.
>>>
>>> Classic symptoms of something heating up. But what?
>>>
>>> - The tuner components are all cold.
>>> - The coax to the balun and its connectors are cold.
>>> - The balun itself is just barely perceptibly warmer (I have to
>>> touch the core to tell).
>>> - The window line, the static drain resistors, the air capacitors
>>> and all the connections in the shack are cold.
>>>
>>> I know the SWR is astronomical on 40 meters, so currents and
>>> voltages are high. But nothing in the shack seems to be heating up.
>>> Any more ideas of where to look?
>>>
>>> --
>>> 73,
>>> Vic, 4X6GP/K2VCO
>>> Rehovot, Israel
>>> http://www.qsl.net/k2vco/
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Re: OT antenna question

Bob McGraw - K4TAX
In reply to this post by Joe Subich, W4TV-4
I'm always fascinated by those which use of a 4:1 balun when 450 ohm
line is used.  In most all cases, the 450 ohm line is operated at a
known high SWR.  The nature of 450 ohm line {or other line such as 300
ohm or 600 ohm, etc.}  is that it exhibits much lower loss when operated
at a high SWR as compared to coax under the same conditions.   The
point...... we are not matching the feed-line impedance.  Even if we
desired to match the feed line, it would need to be terminated into a
450 load.  Even then with a 4:1 balun we would have a ~2.25:1 SWR best
case at the source. [450/4=112.5/50=2.25]

The feed-line basically reflects the impedance of the antenna from the
feed point to the source.  Although at certain electrical lengths of
line it can serve as a 1/4 wave transformer thus transforming the
antenna impedance to another value, we typically find that a 1:1 current
balun is better suited for the application when working between a
balanced line/load and a tuner.

So where does a 4:1 balun become useful?  In general, any place the feed
point of the antenna presents a 200 ohm load.  Example:   a resonant
folded dipole that is less than 1/2 wavelength above the surface of the
earth is typical.  In this example, a 4:1 balun at a 200 ohm load will
present a 50 ohm load to the source.  [200/4=50]

Just remember that most tuners have their greatest loss when the load Z
is less than 50 ohms.   Many tuners being required to match loads in the
5 to 10 ohm range can have as much as 50% to 75% power loss.  This
manifests into heat dissipated in the tuner components and watts of RF
which does not get to the antenna.

  The typical use of a 4:1 balun transformer action will divide the load
by a factor of 4.  Of course one can use a 1:4 balun, in other words,
turn it around to gain some advantage in the impedance matching game.  
Just be sure the balun can handle the voltages involved.    This is a
point for another long discussion.

73
Bob, K4TAX



On 1/12/2016 10:58 PM, Joe Subich, W4TV wrote:

>
> On 1/12/2016 10:57 PM, Bob McGraw K4TAX wrote:
> > If your tuner uses disk ceramic caps, as many do, these can be
> > heating thus not being able to handle the RF current.  They heat
> > and cool and change value which in turn changes tuning.
>
> Particularly if you are using a 4:1 balun!  On 40 meters the impedance
> of the half size antenna is *very low*.  The 4:1 balun will further
> decrease the impedance seen by the tuner causing it to work at its
> absolute worst efficiency (highest circulating current).
>
> At the very least see if you can extend the dipole to 44', then get
> some Smith Chart software and see if you can find a compromise
> feedline length that provides a reasonable impedance on all bands,
> and finally replace the 4:1 balun with a high quality 1:1 current
> balun.
>
> By extending the dipole you should be able to find a compromise
> feedline length that will provide a 100 - 300 Ohm impedance on
> all bands - something the tuner will be much happier to with and
> be far more efficient than working at best than 10 Ohms as it
> probably is doing on 40 meters.
>
> 73,
>
>   ... Joe, W4TV
>
>
> On 1/12/2016 10:57 PM, Bob McGraw K4TAX wrote:
>> If your tuner uses disk ceramic caps, as many do, these can be
>> heating thus not being able to handle the RF current.  They heat and
>> cool and change value which in turn changes tuning.
>>
>> Replacing them with suitable RF current rated units is the solution.
>>
>> Bob, K4TAX
>>
>>
>> Sent from my iPhone
>>
>>> On Jan 12, 2016, at 5:27 PM, Guy Olinger K2AV <[hidden email]>
>>> wrote:
>>>
>>> Hi Vic,
>>>
>>> Your story does suggest trouble at very high current points. Just a
>>> list of
>>> things below I've heard or seen to stir up a new idea or two. No
>>> opinion on
>>> which if any makes any sense in your situation.
>>>
>>> ---------
>>>
>>> Insect nests in tubular spacers on open wire.
>>>
>>> Spacers have carbon tracks.
>>>
>>> Material inside the balun housing is much hotter than touchable
>>> material.
>>>
>>> Stranded wire in open wire has been waterlogged, corroded and the
>>> remaining
>>> conductor material at a current max along the line is heating up.
>>>
>>> Wire inside insulation is nearly all broken, or is broken, and
>>> contact is
>>> miscellaneous and highly resistive.
>>>
>>> Insulation on the wire is significantly compromised by ultra violet or
>>> critter nibbling, letting in water to the stranded conductor.
>>> Advice, has
>>> been to use bare solid #12 copper or larger for open wire that is
>>> carrying
>>> large standing waves, to handle the current maximums.
>>>
>>> Check heat all around the entire core. I have burned up some number of
>>> cores before I understood the materials and engineering. On one all the
>>> damage was on a spot that comprised only 15 degrees of the
>>> circumference.
>>>
>>> Electrical connections in aluminum elements made of telescoping
>>> tubing go
>>> highly resistive as water is boiled out of the joints.
>>>
>>> Connections made of dissimilar metals/materials go bad and become more
>>> resistive as water is boiled out of the joint.
>>>
>>> Tuner rotary switches going bad.
>>>
>>> The rolling contact on on a variable coil losing its tension
>>> (numerous ways
>>> for this to happen depending on construction), contact is very small
>>> and
>>> becomes worse as it heats up. Fixed by repairing mechanism for
>>> maintaining
>>> contact.
>>>
>>> Parted conductors at conductor joints due to metal erosion at the
>>> contact
>>> point.
>>>
>>> --------
>>>
>>> Your troubles would have me taking down the dipole, rebuilding it
>>> with all
>>> mating surfaces wire-brushed and reassembled with clear silicone
>>> dielectric
>>> grease, completely new hardware likewise treated, with all balanced
>>> conductors replaced new, using bare solid #12 outdoors, and brand
>>> new runs
>>> indoors. Old wire to recycling.
>>>
>>> Hope this has kicked off a new idea for you.  73 and good luck.  Guy
>>> K2AV
>>>
>>> On Tue, Jan 12, 2016 at 4:24 PM, Vic Rosenthal 4X6GP/K2VCO <
>>> [hidden email]> wrote:
>>>
>>>> I'm having a problem which has me stumped. I'm going to describe my
>>>> complete antenna and feed system because something in it is
>>>> misbehaving and
>>>> I don't know what!
>>>>
>>>> My system works on all bands from 40 to 10 (or it should).
>>>>
>>>> The antenna is a full-size 20m rotary dipole. It is all aluminum
>>>> tubing,
>>>> no traps or stubs. Just a dipole. I am feeding it with about 30
>>>> feet of
>>>> "true ladder line," which is open wire line made of #16 insulated wire
>>>> spaced about 3-1/4" with black PVC spacers every 18" or so, except
>>>> near the
>>>> antenna and the rotor where I've added extra ones so that the spacing
>>>> doesn't change when the antenna rotates.
>>>>
>>>> The line comes into the shack and is connected to a static drain,
>>>> which is
>>>> a box with two 10-megohm high voltage resistors to ground and a
>>>> couple of
>>>> spark gaps. Then a piece of 450-ohm window line about 3 feet long
>>>> connects
>>>> it to a pair of large air variable capacitors in series with each
>>>> leg which
>>>> knock out some of the reactance on 40m to make it possible to tune
>>>> more
>>>> easily. Then a very short piece of window line connects to a big
>>>> 5kW DX
>>>> Engineering 4:1 balun, spec'ed for tuner service, and finally via a
>>>> piece
>>>> of RG-213 18" long, to a T-network tuner.
>>>>
>>>> My K3 drives a TL922 amp and I have an SWR meter in line.
>>>>
>>>> Now here is my problem: it works OK on all bands except 40 meters.
>>>> On 40,
>>>> it tunes up fine with low power, but when I run more than a couple of
>>>> hundred watts, after perhaps 10 seconds of key-down, the SWR starts to
>>>> climb. I have watched it go to 4:1 before I stop sending for fear of
>>>> destroying something.
>>>>
>>>> The SWR rises both on the meter in the tuner and the extra one I
>>>> have in
>>>> line.
>>>>
>>>> Classic symptoms of something heating up. But what?
>>>>
>>>> - The tuner components are all cold.
>>>> - The coax to the balun and its connectors are cold.
>>>> - The balun itself is just barely perceptibly warmer (I have to
>>>> touch the
>>>> core to tell).
>>>> - The window line, the static drain resistors, the air capacitors
>>>> and all
>>>> the connections in the shack are cold.
>>>>
>>>> I know the SWR is astronomical on 40 meters, so currents and
>>>> voltages are
>>>> high. But nothing in the shack seems to be heating up. Any more
>>>> ideas of
>>>> where to look?
>>>>
>>>> --
>>>> 73,
>>>> Vic, 4X6GP/K2VCO
>>>> Rehovot, Israel
>>>> http://www.qsl.net/k2vco/
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]
>


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Re: OT antenna question

Wes (N7WS)
Generally good info snipped:

Actually at *any* length, other than multiples of one-half wavelength, there is
always some impedance transformation in a mismatched line.

On 1/13/2016 5:40 AM, Bob McGraw K4TAX wrote:
>
> The feed-line basically reflects the impedance of the antenna from the feed
> point to the source.  Although at certain electrical lengths of line it can
> serve as a 1/4 wave transformer thus transforming the antenna impedance to
> another value, we typically find that a 1:1 current balun is better suited for
> the application when working between a balanced line/load and a tuner.
>

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Re: OT antenna question

Don Wilhelm-4
In reply to this post by Joe Subich, W4TV-4
Vic,

Your antenna has a very low feedpoint impedance on 40 meters.  The 30
feet of open wire line plus the 3 feet of 450 ohm is close to a quarter
wavelength on 40 meters.  That feedline length should transform the low
impedance of the dipole to a higher impedance, so the choice of a 4:1
balun *should* be OK.
However, check it - measure the impedance on the coax side of the balun
to see what its value really may be.  If the measured impedance is quite
low, replace the balun with a 1:1 current mode choke - or add about 16
feet (1/8 wavelength on 40 meters) to the parallel feedline and see what
happens to the impedance.

OTOH, you indicate that the SWR changes when you drive it with power.  
That is a sign that something is breaking down in your antenna or
feedline.  That could be a loose connection or some leakage point.  
Leakage across a spacer in your open wire line is one possibility, or
oxidation at any junction in the antenna system.  The clamps of the
copper wire to the aluminum dipole is one suspect area.  Dissimilar
metals will oxidize unless preventative measures are taken.

73,
Don W3FPR

>>>> The antenna is a full-size 20m rotary dipole. It is all aluminum
>>>> tubing,
>>>> no traps or stubs. Just a dipole. I am feeding it with about 30
>>>> feet of
>>>> "true ladder line," which is open wire line made of #16 insulated wire
>>>> spaced about 3-1/4" with black PVC spacers every 18" or so, except
>>>> near the
>>>> antenna and the rotor where I've added extra ones so that the spacing
>>>> doesn't change when the antenna rotates.
>>>>
>>>> The line comes into the shack and is connected to a static drain,
>>>> which is
>>>> a box with two 10-megohm high voltage resistors to ground and a
>>>> couple of
>>>> spark gaps. Then a piece of 450-ohm window line about 3 feet long
>>>> connects
>>>> it to a pair of large air variable capacitors in series with each
>>>> leg which
>>>> knock out some of the reactance on 40m to make it possible to tune
>>>> more
>>>> easily. Then a very short piece of window line connects to a big
>>>> 5kW DX
>>>> Engineering 4:1 balun, spec'ed for tuner service, and finally via a
>>>> piece
>>>> of RG-213 18" long, to a T-network tuner.
>>>>
>>>> My K3 drives a TL922 amp and I have an SWR meter in line.
>>>>
>>>> Now here is my problem: it works OK on all bands except 40 meters.
>>>> On 40,
>>>> it tunes up fine with low power, but when I run more than a couple of
>>>> hundred watts, after perhaps 10 seconds of key-down, the SWR starts to
>>>> climb. I have watched it go to 4:1 before I stop sending for fear of
>>>> destroying something.
>>>>
>>>> The SWR rises both on the meter in the tuner and the extra one I
>>>> have in
>>>> line.
>>>>
>>>> Classic symptoms of something heating up. But what?
>>>>
>>>> - The tuner components are all cold.
>>>> - The coax to the balun and its connectors are cold.
>>>> - The balun itself is just barely perceptibly warmer (I have to
>>>> touch the
>>>> core to tell).
>>>> - The window line, the static drain resistors, the air capacitors
>>>> and all
>>>> the connections in the shack are cold.
>>>>
>>>> I know the SWR is astronomical on 40 meters, so currents and
>>>> voltages are
>>>> high. But nothing in the shack seems to be heating up. Any more
>>>> ideas of
>>>> where to look?
>>>>
>>>> --
>>>> 73,
>>>> Vic, 4X6GP/K2VCO
>>>> Rehovot, Israel
>>>> http://www.qsl.net/k2vco/
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Re: OT antenna question

Al Gulseth-2
In reply to this post by Victor Rosenthal 4X6GP
Bob,

Are silver(ed)/dipped micas (CDE etc.) the preferred type for a tuner, or is
there a superior newer technology available?

TNX/73, Al

On Wed January 13 2016 2:52:52 pm Bob McGraw K4TAX wrote:

>
> If your tuner uses disk ceramic caps, as many do, these can be heating thus
> not being able to handle the RF current.  They heat and cool and change
> value which in turn changes tuning.
>
> Replacing them with suitable RF current rated units is the solution.
>
> Bob, K4TAX
>
>
> Sent from my iPhone
>
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Re: OT antenna question

Bob McGraw - K4TAX
When I updated my 2 tuners, I used some doorknob style capacitors, of
Russian source I presume,  which I purchased via E-Bay. Something like 5
for $20.    These were 470pf units rated at 16KV.    Don't be mislead
with the voltage rating, as it the current handling ability being the
key for RF usage.

In most all cases one will need to provide a somewhat different mounting
as they have screw terminals on either side and are larger physically.  
I just happen to have one in the desk drawer. Typically 1.0" dia x 0.75"
tall with, guessing, #6 or #8 screw terminals on either side.  Could be
Metric screws as I don't recall and can't tell without my thread gauge.

Another approach is to divide the total current  by using 3 or 4 caps in
parallel,  if you wish to use disk ceramic caps.  Thus if your circuit
requires 330 pf then use 3 pcs of 100 pf or 3 pcs of 120 pf in parallel
and keep the voltage rating the same as the originals.  This way the
total current is divided between 3 devices as opposed to one device.  
This also works.

In various transmitter updates, I have used dipped silver mica caps.  
These work well.  Just keep the voltage rating the same as the
originals.  And it won't hurt to use 2 or 3 units parallel by taking the
original capacity value and dividing it  by 2 or 3 for the pf value.    
This approach was used in restoration of some of my old boat anchor AM
transmitters.  These caps are more stable, meaning less tuning drift,
thus work much better than the original disk ceramics units.

73
Bob, K4TAX



On 1/14/2016 8:27 AM, Al Gulseth wrote:

> Bob,
>
> Are silver(ed)/dipped micas (CDE etc.) the preferred type for a tuner, or is
> there a superior newer technology available?
>
> TNX/73, Al
>
> On Wed January 13 2016 2:52:52 pm Bob McGraw K4TAX wrote:
>> If your tuner uses disk ceramic caps, as many do, these can be heating thus
>> not being able to handle the RF current.  They heat and cool and change
>> value which in turn changes tuning.
>>
>> Replacing them with suitable RF current rated units is the solution.
>>
>> Bob, K4TAX
>>
>>
>> Sent from my iPhone
>>


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Re: OT antenna question

David Olean
I bought a bunch of those Russian TX caps. Mine were 680 pf and looked like
the 7.5 KV Centralab ceramic TX caps with threaded holes on each end. I put
two in parallel and used them for the plate blocking capacitor in a 160
meter KW triode amplifier. Big mistake. They cannot handle much current at
all. When I keyed the amp, I saw the power output drop very fast. Those caps
got very hot and failed miserably. I complained to the eBay seller and he
advised that they were only for use as bypass caps and should not be used
directly in the TX line. (Silly me!) Their heating cycle reminded me of what
happened with Vic's antenna system of late.
    I still have them. They might make good target practice subjects. Buyer
beware.

K1WHS

----- Original Message -----
From: "Bob McGraw K4TAX" <[hidden email]>
To: <[hidden email]>; <[hidden email]>
Sent: Thursday, January 14, 2016 2:47 PM
Subject: Re: [Elecraft] OT antenna question


> When I updated my 2 tuners, I used some doorknob style capacitors, of
> Russian source I presume,  which I purchased via E-Bay. Something like 5
> for $20.    These were 470pf units rated at 16KV.    Don't be mislead with
> the voltage rating, as it the current handling ability being the key for
> RF usage.
>
> In most all cases one will need to provide a somewhat different mounting
> as they have screw terminals on either side and are larger physically.  I
> just happen to have one in the desk drawer. Typically 1.0" dia x 0.75"
> tall with, guessing, #6 or #8 screw terminals on either side.  Could be
> Metric screws as I don't recall and can't tell without my thread gauge.
>
> Another approach is to divide the total current  by using 3 or 4 caps in
> parallel,  if you wish to use disk ceramic caps.  Thus if your circuit
> requires 330 pf then use 3 pcs of 100 pf or 3 pcs of 120 pf in parallel
> and keep the voltage rating the same as the originals.  This way the total
> current is divided between 3 devices as opposed to one device.  This also
> works.
>
> In various transmitter updates, I have used dipped silver mica caps.
> These work well.  Just keep the voltage rating the same as the originals.
> And it won't hurt to use 2 or 3 units parallel by taking the original
> capacity value and dividing it  by 2 or 3 for the pf value.    This
> approach was used in restoration of some of my old boat anchor AM
> transmitters.  These caps are more stable, meaning less tuning drift, thus
> work much better than the original disk ceramics units.
>
> 73
> Bob, K4TAX
>
>
>
> On 1/14/2016 8:27 AM, Al Gulseth wrote:
>> Bob,
>>
>> Are silver(ed)/dipped micas (CDE etc.) the preferred type for a tuner, or
>> is
>> there a superior newer technology available?
>>
>> TNX/73, Al
>>
>> On Wed January 13 2016 2:52:52 pm Bob McGraw K4TAX wrote:
>>> If your tuner uses disk ceramic caps, as many do, these can be heating
>>> thus
>>> not being able to handle the RF current.  They heat and cool and change
>>> value which in turn changes tuning.
>>>
>>> Replacing them with suitable RF current rated units is the solution.
>>>
>>> Bob, K4TAX
>>>
>>>
>>> Sent from my iPhone
>>>
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]

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Re: OT antenna question

Al Gulseth-2
I should clarify that I was thinking in terms of ~ 100W. There's always the
old standby of Jennings vacuum variables for QRO use....

73, Al

On Thu January 14 2016 9:44:04 am Dave Olean wrote:

> I bought a bunch of those Russian TX caps. Mine were 680 pf and looked like
> the 7.5 KV Centralab ceramic TX caps with threaded holes on each end. I put
> two in parallel and used them for the plate blocking capacitor in a 160
> meter KW triode amplifier. Big mistake. They cannot handle much current at
> all. When I keyed the amp, I saw the power output drop very fast. Those
> caps got very hot and failed miserably. I complained to the eBay seller and
> he advised that they were only for use as bypass caps and should not be
> used directly in the TX line. (Silly me!) Their heating cycle reminded me
> of what happened with Vic's antenna system of late.
>     I still have them. They might make good target practice subjects. Buyer
> beware.
>
> K1WHS
>
> ----- Original Message -----
> From: "Bob McGraw K4TAX" <[hidden email]>
> To: <[hidden email]>; <[hidden email]>
> Sent: Thursday, January 14, 2016 2:47 PM
> Subject: Re: [Elecraft] OT antenna question
>
> > When I updated my 2 tuners, I used some doorknob style capacitors, of
> > Russian source I presume,  which I purchased via E-Bay. Something like 5
> > for $20.    These were 470pf units rated at 16KV.    Don't be mislead
> > with the voltage rating, as it the current handling ability being the key
> > for RF usage.
> >
> > In most all cases one will need to provide a somewhat different mounting
> > as they have screw terminals on either side and are larger physically.  I
> > just happen to have one in the desk drawer. Typically 1.0" dia x 0.75"
> > tall with, guessing, #6 or #8 screw terminals on either side.  Could be
> > Metric screws as I don't recall and can't tell without my thread gauge.
> >
> > Another approach is to divide the total current  by using 3 or 4 caps in
> > parallel,  if you wish to use disk ceramic caps.  Thus if your circuit
> > requires 330 pf then use 3 pcs of 100 pf or 3 pcs of 120 pf in parallel
> > and keep the voltage rating the same as the originals.  This way the
> > total current is divided between 3 devices as opposed to one device.
> > This also works.
> >
> > In various transmitter updates, I have used dipped silver mica caps.
> > These work well.  Just keep the voltage rating the same as the originals.
> > And it won't hurt to use 2 or 3 units parallel by taking the original
> > capacity value and dividing it  by 2 or 3 for the pf value.    This
> > approach was used in restoration of some of my old boat anchor AM
> > transmitters.  These caps are more stable, meaning less tuning drift,
> > thus work much better than the original disk ceramics units.
> >
> > 73
> > Bob, K4TAX
> >
> > On 1/14/2016 8:27 AM, Al Gulseth wrote:
> >> Bob,
> >>
> >> Are silver(ed)/dipped micas (CDE etc.) the preferred type for a tuner,
> >> or is
> >> there a superior newer technology available?
> >>
> >> TNX/73, Al
> >>
> >> On Wed January 13 2016 2:52:52 pm Bob McGraw K4TAX wrote:
> >>> If your tuner uses disk ceramic caps, as many do, these can be heating
> >>> thus
> >>> not being able to handle the RF current.  They heat and cool and change
> >>> value which in turn changes tuning.
> >>>
> >>> Replacing them with suitable RF current rated units is the solution.
> >>>
> >>> Bob, K4TAX
> >>>
> >>>
> >>> Sent from my iPhone
> >
> > ______________________________________________________________
> > Elecraft mailing list
> > Home: http://mailman.qth.net/mailman/listinfo/elecraft
> > Help: http://mailman.qth.net/mmfaq.htm
> > Post: mailto:[hidden email]
> >
> > This list hosted by: http://www.qsl.net
> > Please help support this email list: http://www.qsl.net/donate.html
> > Message delivered to [hidden email]
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Re: OT antenna question

Bob McGraw - K4TAX
In reply to this post by David Olean
First I'd say 680 pf , two parallel, is not at all adequate for a 160M
KW amp.  More like 4 would be expected for about 2800 pf total required
for 160M  depending on plate Z.      Also with 3200 volts or so, again
depending on the plate Z, 7.5 KV again is not much margin of safety.    
Ep x 4 is about right.

Just my comments and data from a Pi L calculator.

73
Bob, K4TAX



On 1/14/2016 9:44 AM, Dave Olean wrote:

> I bought a bunch of those Russian TX caps. Mine were 680 pf and looked
> like the 7.5 KV Centralab ceramic TX caps with threaded holes on each
> end. I put two in parallel and used them for the plate blocking
> capacitor in a 160 meter KW triode amplifier. Big mistake. They cannot
> handle much current at all. When I keyed the amp, I saw the power
> output drop very fast. Those caps got very hot and failed miserably. I
> complained to the eBay seller and he advised that they were only for
> use as bypass caps and should not be used directly in the TX line.
> (Silly me!) Their heating cycle reminded me of what happened with
> Vic's antenna system of late.
>    I still have them. They might make good target practice subjects.
> Buyer beware.
>
> K1WHS
>
> ----- Original Message ----- From: "Bob McGraw K4TAX"
> <[hidden email]>
> To: <[hidden email]>; <[hidden email]>
> Sent: Thursday, January 14, 2016 2:47 PM
> Subject: Re: [Elecraft] OT antenna question
>
>
>> When I updated my 2 tuners, I used some doorknob style capacitors, of
>> Russian source I presume,  which I purchased via E-Bay. Something
>> like 5 for $20.    These were 470pf units rated at 16KV.    Don't be
>> mislead with the voltage rating, as it the current handling ability
>> being the key for RF usage.
>>
>> In most all cases one will need to provide a somewhat different
>> mounting as they have screw terminals on either side and are larger
>> physically.  I just happen to have one in the desk drawer. Typically
>> 1.0" dia x 0.75" tall with, guessing, #6 or #8 screw terminals on
>> either side.  Could be Metric screws as I don't recall and can't tell
>> without my thread gauge.
>>
>> Another approach is to divide the total current  by using 3 or 4 caps
>> in parallel,  if you wish to use disk ceramic caps.  Thus if your
>> circuit requires 330 pf then use 3 pcs of 100 pf or 3 pcs of 120 pf
>> in parallel and keep the voltage rating the same as the originals.  
>> This way the total current is divided between 3 devices as opposed to
>> one device.  This also works.
>>
>> In various transmitter updates, I have used dipped silver mica caps.
>> These work well.  Just keep the voltage rating the same as the
>> originals. And it won't hurt to use 2 or 3 units parallel by taking
>> the original capacity value and dividing it  by 2 or 3 for the pf
>> value.    This approach was used in restoration of some of my old
>> boat anchor AM transmitters.  These caps are more stable, meaning
>> less tuning drift, thus work much better than the original disk
>> ceramics units.
>>
>> 73
>> Bob, K4TAX
>>
>>
>>
>> On 1/14/2016 8:27 AM, Al Gulseth wrote:
>>> Bob,
>>>
>>> Are silver(ed)/dipped micas (CDE etc.) the preferred type for a
>>> tuner, or is
>>> there a superior newer technology available?
>>>
>>> TNX/73, Al
>>>
>>> On Wed January 13 2016 2:52:52 pm Bob McGraw K4TAX wrote:
>>>> If your tuner uses disk ceramic caps, as many do, these can be
>>>> heating thus
>>>> not being able to handle the RF current.  They heat and cool and
>>>> change
>>>> value which in turn changes tuning.
>>>>
>>>> Replacing them with suitable RF current rated units is the solution.
>>>>
>>>> Bob, K4TAX
>>>>
>>>>
>>>> Sent from my iPhone
>>>>
>>
>>
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>> Message delivered to [hidden email]
>
>


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Re: OT antenna question

Igor Sokolov-2
I wish to second Bob and also add that Russian TX capacitors are usually
labled not only with max voltage but also with max power they can handle. In
Russian that is printed as XX KBAP which stands for Kili Volt Amp Reactive
power. And XX is the number.

73, Igor UA9CDC
----- Original Message -----
From: "Bob McGraw K4TAX" <[hidden email]>
To: "Dave Olean" <[hidden email]>; <[hidden email]>;
<[hidden email]>
Sent: Thursday, January 14, 2016 8:56 PM
Subject: Re: [Elecraft] OT antenna question


> First I'd say 680 pf , two parallel, is not at all adequate for a 160M KW
> amp.  More like 4 would be expected for about 2800 pf total required for
> 160M  depending on plate Z.      Also with 3200 volts or so, again
> depending on the plate Z, 7.5 KV again is not much margin of safety.    Ep
> x 4 is about right.
>
> Just my comments and data from a Pi L calculator.
>
> 73
> Bob, K4TAX
>
>
>
> On 1/14/2016 9:44 AM, Dave Olean wrote:
>> I bought a bunch of those Russian TX caps. Mine were 680 pf and looked
>> like the 7.5 KV Centralab ceramic TX caps with threaded holes on each
>> end. I put two in parallel and used them for the plate blocking capacitor
>> in a 160 meter KW triode amplifier. Big mistake. They cannot handle much
>> current at all. When I keyed the amp, I saw the power output drop very
>> fast. Those caps got very hot and failed miserably. I complained to the
>> eBay seller and he advised that they were only for use as bypass caps and
>> should not be used directly in the TX line. (Silly me!) Their heating
>> cycle reminded me of what happened with Vic's antenna system of late.
>>    I still have them. They might make good target practice subjects.
>> Buyer beware.
>>
>> K1WHS
>>
>> ----- Original Message ----- From: "Bob McGraw K4TAX"
>> <[hidden email]>
>> To: <[hidden email]>; <[hidden email]>
>> Sent: Thursday, January 14, 2016 2:47 PM
>> Subject: Re: [Elecraft] OT antenna question
>>
>>
>>> When I updated my 2 tuners, I used some doorknob style capacitors, of
>>> Russian source I presume,  which I purchased via E-Bay. Something like 5
>>> for $20.    These were 470pf units rated at 16KV.    Don't be mislead
>>> with the voltage rating, as it the current handling ability being the
>>> key for RF usage.
>>>
>>> In most all cases one will need to provide a somewhat different mounting
>>> as they have screw terminals on either side and are larger physically.
>>> I just happen to have one in the desk drawer. Typically 1.0" dia x 0.75"
>>> tall with, guessing, #6 or #8 screw terminals on either side.  Could be
>>> Metric screws as I don't recall and can't tell without my thread gauge.
>>>
>>> Another approach is to divide the total current  by using 3 or 4 caps in
>>> parallel,  if you wish to use disk ceramic caps.  Thus if your circuit
>>> requires 330 pf then use 3 pcs of 100 pf or 3 pcs of 120 pf in parallel
>>> and keep the voltage rating the same as the originals.  This way the
>>> total current is divided between 3 devices as opposed to one device.
>>> This also works.
>>>
>>> In various transmitter updates, I have used dipped silver mica caps.
>>> These work well.  Just keep the voltage rating the same as the
>>> originals. And it won't hurt to use 2 or 3 units parallel by taking the
>>> original capacity value and dividing it  by 2 or 3 for the pf value.
>>> This approach was used in restoration of some of my old boat anchor AM
>>> transmitters.  These caps are more stable, meaning less tuning drift,
>>> thus work much better than the original disk ceramics units.
>>>
>>> 73
>>> Bob, K4TAX
>>>
>>>
>>>
>>> On 1/14/2016 8:27 AM, Al Gulseth wrote:
>>>> Bob,
>>>>
>>>> Are silver(ed)/dipped micas (CDE etc.) the preferred type for a tuner,
>>>> or is
>>>> there a superior newer technology available?
>>>>
>>>> TNX/73, Al
>>>>
>>>> On Wed January 13 2016 2:52:52 pm Bob McGraw K4TAX wrote:
>>>>> If your tuner uses disk ceramic caps, as many do, these can be heating
>>>>> thus
>>>>> not being able to handle the RF current.  They heat and cool and
>>>>> change
>>>>> value which in turn changes tuning.
>>>>>
>>>>> Replacing them with suitable RF current rated units is the solution.
>>>>>
>>>>> Bob, K4TAX
>>>>>
>>>>>
>>>>> Sent from my iPhone
>>>>>
>>>
>>>
>>> ______________________________________________________________
>>> Elecraft mailing list
>>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>>> Help: http://mailman.qth.net/mmfaq.htm
>>> Post: mailto:[hidden email]
>>>
>>> This list hosted by: http://www.qsl.net
>>> Please help support this email list: http://www.qsl.net/donate.html
>>> Message delivered to [hidden email]
>>
>>
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]

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Re: OT antenna question

Alan Bloom
In reply to this post by Bob McGraw - K4TAX
This is good advice.  Ceramic capacitors can have very low loss - it
depends on the dielectric used.  Smaller value NPO (zero temperature
coefficient) types tend to have the lowest loss.  Large value X7R, Z5U,
etc. types have very high loss and are generally unsuitable for any
high-current RF application.

The type of doorknob ceramic caps that you can find in old tube-type TV
sets are the high-loss type.  OK for bypass capacitors but not for a tuner.

Using several capacitors in parallel to split the current is a good
idea.  It also reduces the stray inductance.

Alan N1AL


On 01/14/2016 06:47 AM, Bob McGraw K4TAX wrote:

> When I updated my 2 tuners, I used some doorknob style capacitors, of
> Russian source I presume,  which I purchased via E-Bay. Something like 5
> for $20.    These were 470pf units rated at 16KV.    Don't be mislead
> with the voltage rating, as it the current handling ability being the
> key for RF usage.
>
> In most all cases one will need to provide a somewhat different mounting
> as they have screw terminals on either side and are larger physically. I
> just happen to have one in the desk drawer. Typically 1.0" dia x 0.75"
> tall with, guessing, #6 or #8 screw terminals on either side.  Could be
> Metric screws as I don't recall and can't tell without my thread gauge.
>
> Another approach is to divide the total current  by using 3 or 4 caps in
> parallel,  if you wish to use disk ceramic caps.  Thus if your circuit
> requires 330 pf then use 3 pcs of 100 pf or 3 pcs of 120 pf in parallel
> and keep the voltage rating the same as the originals.  This way the
> total current is divided between 3 devices as opposed to one device.
> This also works.
>
> In various transmitter updates, I have used dipped silver mica caps.
> These work well.  Just keep the voltage rating the same as the
> originals.  And it won't hurt to use 2 or 3 units parallel by taking the
> original capacity value and dividing it  by 2 or 3 for the pf value.
> This approach was used in restoration of some of my old boat anchor AM
> transmitters.  These caps are more stable, meaning less tuning drift,
> thus work much better than the original disk ceramics units.
>
> 73
> Bob, K4TAX
>
>
>
> On 1/14/2016 8:27 AM, Al Gulseth wrote:
>> Bob,
>>
>> Are silver(ed)/dipped micas (CDE etc.) the preferred type for a tuner,
>> or is
>> there a superior newer technology available?
>>
>> TNX/73, Al
>>
>> On Wed January 13 2016 2:52:52 pm Bob McGraw K4TAX wrote:
>>> If your tuner uses disk ceramic caps, as many do, these can be
>>> heating thus
>>> not being able to handle the RF current.  They heat and cool and change
>>> value which in turn changes tuning.
>>>
>>> Replacing them with suitable RF current rated units is the solution.
>>>
>>> Bob, K4TAX
>>>
>>>
>>> Sent from my iPhone
>>>
>
>
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