KPA1500 RFI on 12m

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KPA1500 RFI on 12m

Elecraft mailing list
My Force 12 C3 antenna is not resonant on 12m.  Using the K3 barefoot, the internal atu tunes the antenna fine.  Bypassing the K3 atu, but still running barefoot into the KPA1500 atu, the KPA atu loses it's mind and goes in and out of TUNE mode uncommanded.  Even though the KPA has found a match, trying to transmit through it at the 100w level is impossible because of the constant retuning.
I have put my small collection of mix-31 ferrites on the antenna output, input, and KPA control line at the KPA, each at a time, with no success.  Any ideas?  I would like to be able to run the KPA at least a few hundred watts to have the proverbial snowball's chance to break the VP6R pileup on 12m CW.
Any useful comments appreciated.
73 Eric WD6DBM

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Re: KPA1500 RFI on 12m

Michael Walker
Hi Eric

I think you are asking a lot for a tuner to run at any power into a
non-resonant antenna and break a pile up.  :)

You would actually have better success with a 12M dipole then trying to get
a non-resonant beam to direct your signal.

If I was in your shoes, I would quickly toss up a 12M dipole with some
string and bubble gum as you would have a much higher radiated signal.

Mike va3mw


On Thu, Oct 24, 2019 at 4:08 PM eric norris via Elecraft <
[hidden email]> wrote:

> My Force 12 C3 antenna is not resonant on 12m.  Using the K3 barefoot, the
> internal atu tunes the antenna fine.  Bypassing the K3 atu, but still
> running barefoot into the KPA1500 atu, the KPA atu loses it's mind and goes
> in and out of TUNE mode uncommanded.  Even though the KPA has found a
> match, trying to transmit through it at the 100w level is impossible
> because of the constant retuning.
> I have put my small collection of mix-31 ferrites on the antenna output,
> input, and KPA control line at the KPA, each at a time, with no success.
> Any ideas?  I would like to be able to run the KPA at least a few hundred
> watts to have the proverbial snowball's chance to break the VP6R pileup on
> 12m CW.
> Any useful comments appreciated.
> 73 Eric WD6DBM
>
> Sent from Yahoo Mail on Android
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
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Re: KPA1500 RFI on 12m

Dave wo2x
I have similar weirdness on 60 meters using the tuner in the radio with the amp in standby and amp tuner bypassed.  The amp wattmeter shows 276 watts reflected and the amp tuner keeps trying to automatically engage.

Something in the amp logic will not allow it to be in pass through but after the radio tuner. I have to have the amp off when running 60 meters. Not a big deal but there is something weird with the SWR detection in the KPA1500 which allows it to take the amp tuner out of bypass.

Dave wo2x



Sent from my waxed string and tin cans.

> On Oct 24, 2019, at 4:26 PM, Michael Walker <[hidden email]> wrote:
>
> Hi Eric
>
> I think you are asking a lot for a tuner to run at any power into a
> non-resonant antenna and break a pile up.  :)
>
> You would actually have better success with a 12M dipole then trying to get
> a non-resonant beam to direct your signal.
>
> If I was in your shoes, I would quickly toss up a 12M dipole with some
> string and bubble gum as you would have a much higher radiated signal.
>
> Mike va3mw
>
>
>> On Thu, Oct 24, 2019 at 4:08 PM eric norris via Elecraft <
>> [hidden email]> wrote:
>>
>> My Force 12 C3 antenna is not resonant on 12m.  Using the K3 barefoot, the
>> internal atu tunes the antenna fine.  Bypassing the K3 atu, but still
>> running barefoot into the KPA1500 atu, the KPA atu loses it's mind and goes
>> in and out of TUNE mode uncommanded.  Even though the KPA has found a
>> match, trying to transmit through it at the 100w level is impossible
>> because of the constant retuning.
>> I have put my small collection of mix-31 ferrites on the antenna output,
>> input, and KPA control line at the KPA, each at a time, with no success.
>> Any ideas?  I would like to be able to run the KPA at least a few hundred
>> watts to have the proverbial snowball's chance to break the VP6R pileup on
>> 12m CW.
>> Any useful comments appreciated.
>> 73 Eric WD6DBM
>>
>> Sent from Yahoo Mail on Android
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
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>> Please help support this email list: http://www.qsl.net/donate.html
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Re: KPA1500 RFI on 12m

john@kk9a.com
In reply to this post by Elecraft mailing list
I have a C3 that I brought to St Croix and operated as WP2AA. It has no 12m
elements however the manual states it will work on 12m with a tuner although
I am not sure what the pattern would be. I am not a fan of using out of
resonant antennas and do not even have a tuner in any of my K3S's. I wonder
what the C3 SWR is on 12? The KPA1500 specs are for a maximum SWR of 3:1,
perhaps an external tuner is needed?

John KK9A



eric norris WD6DBM wrote:

My Force 12 C3 antenna is not resonant on 12m.  Using the K3 barefoot, the
internal atu tunes the antenna fine.  Bypassing the K3 atu, but still
running barefoot into the KPA1500 atu, the KPA atu loses it's mind and goes
in and out of TUNE mode uncommanded.  Even though the KPA has found a match,
trying to transmit through it at the 100w level is impossible because of the
constant retuning.
I have put my small collection of mix-31 ferrites on the antenna output,
input, and KPA control line at the KPA, each at a time, with no success.
Any ideas?  I would like to be able to run the KPA at least a few hundred
watts to have the proverbial snowball's chance to break the VP6R pileup on
12m CW.
Any useful comments appreciated.
73 Eric WD6DBM

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Re: KPA1500 RFI on 12m

Dave wo2x
I had a C3SS. From what I remember the amp tuner should be able to handle the SWR. I think the pattern on 12 was 180 degrees from normal heading.

Dave wo2x

Sent from my iPad

> On Oct 24, 2019, at 9:58 PM, [hidden email] wrote:
>
> I have a C3 that I brought to St Croix and operated as WP2AA. It has no 12m
> elements however the manual states it will work on 12m with a tuner although
> I am not sure what the pattern would be. I am not a fan of using out of
> resonant antennas and do not even have a tuner in any of my K3S's. I wonder
> what the C3 SWR is on 12? The KPA1500 specs are for a maximum SWR of 3:1,
> perhaps an external tuner is needed?
>
> John KK9A
>
>
>
> eric norris WD6DBM wrote:
>
> My Force 12 C3 antenna is not resonant on 12m.  Using the K3 barefoot, the
> internal atu tunes the antenna fine.  Bypassing the K3 atu, but still
> running barefoot into the KPA1500 atu, the KPA atu loses it's mind and goes
> in and out of TUNE mode uncommanded.  Even though the KPA has found a match,
> trying to transmit through it at the 100w level is impossible because of the
> constant retuning.
> I have put my small collection of mix-31 ferrites on the antenna output,
> input, and KPA control line at the KPA, each at a time, with no success.
> Any ideas?  I would like to be able to run the KPA at least a few hundred
> watts to have the proverbial snowball's chance to break the VP6R pileup on
> 12m CW.
> Any useful comments appreciated.
> 73 Eric WD6DBM
>
> ______________________________________________________________
> 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: KPA1500 RFI on 12m

Jim Brown-10
In reply to this post by Elecraft mailing list
On 10/24/2019 1:08 PM, eric norris via Elecraft wrote:
> My Force 12 C3 antenna is not resonant on 12m.  Using the K3 barefoot, the internal atu tunes the antenna fine.  Bypassing the K3 atu, but still running barefoot into the KPA1500 atu, the KPA atu loses it's mind and goes in and out of TUNE mode uncommanded.  Even though the KPA has found a match, trying to transmit through it at the 100w level is impossible because of the constant retuning.
> I have put my small collection of mix-31 ferrites on the antenna output, input, and KPA control line at the KPA, each at a time, with no success.  Any ideas?

Yes. First, and most important, the place for the common mode choke is
at the antenna feedpoint, NOT in the shack, and it must be a
well-designed multi-turn choke. http://k9yc.com/2018Cookbook.pdf

Second, make sure that you entire station is properly bonded,
chassis-to-chassis of all interconnected equipment, and that operating
desk bonded to every ground in your home.
http://k9yc.com/GroundingAndAudio.pdf

Also, this is a good time to verify that EVERY  coax connector and
adapter has its shield well terminated (well soldered or properly
crimped) and that all solder-type connectors are an Amphenol 83-1SP.
Make sure that all adapters are Amphenol or have a MIL-spec part number
stamped on them. Off-brand connectors are often junk, and often cause
problems like what you're seeing. Also make sure that every connector is
wrench-tight.

Station design issues like these may not show up at low power but cause
problems with high power.

73, Jim K9YC

   I would like to be able to run the KPA at least a few hundred watts
to have the proverbial snowball's chance to break the VP6R pileup on 12m CW.

> Any useful comments appreciated.
> 73 Eric WD6DBM
>
> Sent from Yahoo Mail on Android
> ______________________________________________________________
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> Message delivered to [hidden email]
>

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Re: KPA1500 RFI on 12m

John Oppenheimer
In reply to this post by Elecraft mailing list
Hi Eric,

What is the measured SWR on 12M?

Way different band, worked VP6R 40M CW using K2 at ~15 watts and ground
plane 19' vertical.

John KN5L

On 10/24/19 3:08 PM, eric norris via Elecraft wrote:
> Force 12 C3 antenna is not resonant on 12m.  Using the K3 barefoot, the internal atu tunes the antenna fine.  Bypassing the K3 atu, but still running barefoot into the KPA1500 atu, the KPA atu loses it's mind and goes in and out of TUNE mode uncommanded
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KPA1500 RFI on 12m

ANDY DURBIN
In reply to this post by Elecraft mailing list
"Not a big deal but there is something weird with the SWR detection in the KPA1500 which allows it to take the amp tuner out of bypass. "

I don't know the KPA1500 tuner but all the annoying changes in tuning solution of my KAT500 were fixed by defeating RF frequency detection.  Is your tuner perhaps selecting an adjacent frequency bin for which the stored solution is not bypass?

Andy, k3wyc
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Re: KPA1500 RFI on 12m

Dave wo2x
In reply to this post by Elecraft mailing list
In the KPA1500 utility I have the tuner bypassed for the whole 60 meter band. The tuner’s logic is detecting a high SWR and overriding the bypass selection. This happens at 30 watts forward power.

The answer is to turn off the amp when on 60 and just use the radio’s tuner.

Dave wo2x

Sent from my waxed string and tin cans.

> On Oct 25, 2019, at 8:17 AM, Andy Durbin <[hidden email]> wrote:
>
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Re: KPA1500 RFI on 12m

ANDY DURBIN
In reply to this post by ANDY DURBIN
"Not a big deal but there is something weird with the SWR detection in the KPA1500 which allows it to take the amp tuner out of bypass. "

It also seems possible that the tuning solution change is triggered by "high SWR threshold".   Read the Programming Reference information for commands ^HS; and ^STA; for more info.  If this is the cause then setting ^HS0; may help.  You will need to use the Utility to inspect and change the values.

Sometimes we will accept less than ideal antennas when chasing DX and sometimes we get lucky.

Andy, k3wyc

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Re: KPA1500 RFI on 12m

K8TE
In reply to this post by Dave wo2x
What is a big deal is using the KPA1500 on 60m unless you're using a dummy
load or paper clip for an antenna.  "The 60 meter band has special
restrictions including the restriction of radiated power relative to the
gain of a half-wavelength dipole antenna which is 100 watts PEP."  We need
to keep 60m, not loose it due to abusing its power limit.

The KPA1500 tuner can achieve solutions beyond VSWR's of 3:1, but only if
running reduced power.  See page 18 of the Rev B manual for the VSWR vs.
power curve.

73, Bill, K8TE
KPA1500 S/N 116



--
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Re: KPA1500 RFI on 12m

Wes Stewart-2
In reply to this post by Michael Walker
I run a KPA500 and KAT500 into an Ppitbe

Sent from my iPhone

> On Oct 24, 2019, at 1:24 PM, Michael Walker <[hidden email]> wrote:
>
> Hi Eric
>
> I think you are asking a lot for a tuner to run at any power into a
> non-resonant antenna and break a pile up.  :)
>
> You would actually have better success with a 12M dipole then trying to get
> a non-resonant beam to direct your signal.
>
> If I was in your shoes, I would quickly toss up a 12M dipole with some
> string and bubble gum as you would have a much higher radiated signal.
>
> Mike va3mw
>
>
> On Thu, Oct 24, 2019 at 4:08 PM eric norris via Elecraft <
> [hidden email]> wrote:
>
>> My Force 12 C3 antenna is not resonant on 12m.  Using the K3 barefoot, the
>> internal atu tunes the antenna fine.  Bypassing the K3 atu, but still
>> running barefoot into the KPA1500 atu, the KPA atu loses it's mind and goes
>> in and out of TUNE mode uncommanded.  Even though the KPA has found a
>> match, trying to transmit through it at the 100w level is impossible
>> because of the constant retuning.
>> I have put my small collection of mix-31 ferrites on the antenna output,
>> input, and KPA control line at the KPA, each at a time, with no success.
>> Any ideas?  I would like to be able to run the KPA at least a few hundred
>> watts to have the proverbial snowball's chance to break the VP6R pileup on
>> 12m CW.
>> Any useful comments appreciated.
>> 73 Eric WD6DBM
>>
>> Sent from Yahoo Mail on Android
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
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>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
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Re: KPA1500 RFI on 12m

Martin Sole-3
In reply to this post by Elecraft mailing list
I use a C3 up at 80 feet it works quite well. I have not really spent a
lot of time on 12m, really no activity here to make it worthwhile but on
17m it works rather well despite not being a particularly good match. I
fixed that by measuring the actual impedance at the end of my feeder
then adding a foot or so of feeder and cutting a shorted stub to create
a good match. In my case it's very close to perfect but anything less
than 1.5:1 I would consider excellent.

An antenna analyser and 5 minutes with the excellent SimSmith program
can do wonders for your matching worries. Properly sorted at just the
right point on the feeder with an antenna switch a tee piece and a few
stubs you could probably get a good match on a bunch of bands though I
suspect the losses might be a bit high if you try 40m, eek!

The C3 on 17m certainly has directivity albeit 180 degree from the
regular 20-15-10 antenna.

Martin, HS0ZED






On 25/10/2019 03:08, eric norris via Elecraft wrote:

> My Force 12 C3 antenna is not resonant on 12m.  Using the K3 barefoot, the internal atu tunes the antenna fine.  Bypassing the K3 atu, but still running barefoot into the KPA1500 atu, the KPA atu loses it's mind and goes in and out of TUNE mode uncommanded.  Even though the KPA has found a match, trying to transmit through it at the 100w level is impossible because of the constant retuning.
> I have put my small collection of mix-31 ferrites on the antenna output, input, and KPA control line at the KPA, each at a time, with no success.  Any ideas?  I would like to be able to run the KPA at least a few hundred watts to have the proverbial snowball's chance to break the VP6R pileup on 12m CW.
> Any useful comments appreciated.
> 73 Eric WD6DBM
>
> Sent from Yahoo Mail on Android
> ______________________________________________________________
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> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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Re: KPA1500 RFI on 12m

Wes Stewart-2
In reply to this post by Wes Stewart-2
Sorry about that mess; that will teach me to try and respond with an iPhone.

What I was trying to say is that I run a KPA500 and KAT500 into non-resonant
antennas on all of the WARC bands and still manage to crack pileups.  On 12 and
17 meters I tune my tiny OB7-3 Optibeam tribander.  Of the current DXpeditions, 
I've worked VP6R on 19 slots and I work FT8 with great reluctance.  I've worked
5K0K on 14 of 25 slots without using FT8.  For the recently completed ZK3A
expedition I worked them of 24 of 37 slots and was on Clublog's stats number 20
in NA.

I'm pretty sure that I never have the commanding signal in a pileup.  BTW, I use
a K3S without a second RX and I don't have a separate RX antenna for 160, things
everybody knows you must have to work DX.  IMHO, knowing how to use the hardware
you have is more important than having more hardware.

Wes  N7WS


On 10/25/2019 9:00 AM, Wes N7WS wrote:

> I run a KPA500 and KAT500 into an Ppitbe
>
> Sent from my iPhone
>
>> On Oct 24, 2019, at 1:24 PM, Michael Walker <[hidden email]> wrote:
>>
>> Hi Eric
>>
>> I think you are asking a lot for a tuner to run at any power into a
>> non-resonant antenna and break a pile up.  :)
>>
>> You would actually have better success with a 12M dipole then trying to get
>> a non-resonant beam to direct your signal.
>>
>> If I was in your shoes, I would quickly toss up a 12M dipole with some
>> string and bubble gum as you would have a much higher radiated signal.
>>
>> Mike va3mw
>>

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Re: KPA1500 RFI on 12m

Bob McGraw - K4TAX
Except for my 6M yagi, all of my antennas are non-resonant antennas.  
My favorite is the 256 ft center fed wire {resonant at 1.825 MHz}  with
a balanced feed.  The  balanced feed runs from the feed-point on the
antenna all the way to the hybrid Guanella 4:1 balun that sits on the
shelf just above the KAT500.  The coax jumper from the balun to the
KAT500 is about 12" in length.   Thus the balanced line comes in all the
way to the operating position.    This configuration will work all
bands,  160M - 6M with ease. And there are NO RFI issues with the KPA500
and the KAT-500 at 500 watts.

I find most hams cut an antenna length by formula, leave a few inches to
trim, and then trim for best SWR.   This does not make a resonant
antenna.    A resonant antenna is resonant depending on its electrical
length based on frequency.   SWR and Impedance should be addressed by
means than trimming the length.   Height above ground affects impedance.

73

Bob, K4TAX


On 10/25/2019 3:37 PM, Wes wrote:

> Sorry about that mess; that will teach me to try and respond with an
> iPhone.
>
> What I was trying to say is that I run a KPA500 and KAT500 into
> non-resonant antennas on all of the WARC bands and still manage to
> crack pileups.  On 12 and 17 meters I tune my tiny OB7-3 Optibeam
> tribander.  Of the current DXpeditions,  I've worked VP6R on 19 slots
> and I work FT8 with great reluctance.  I've worked 5K0K on 14 of 25
> slots without using FT8.  For the recently completed ZK3A expedition I
> worked them of 24 of 37 slots and was on Clublog's stats number 20 in NA.
>
> I'm pretty sure that I never have the commanding signal in a pileup. 
> BTW, I use a K3S without a second RX and I don't have a separate RX
> antenna for 160, things everybody knows you must have to work DX. 
> IMHO, knowing how to use the hardware you have is more important than
> having more hardware.
>
> Wes  N7WS
>
>
> On 10/25/2019 9:00 AM, Wes N7WS wrote:
>> I run a KPA500 and KAT500 into an Ppitbe
>>
>> Sent from my iPhone
>>
>>> On Oct 24, 2019, at 1:24 PM, Michael Walker <[hidden email]>
>>> wrote:
>>>
>>> Hi Eric
>>>
>>> I think you are asking a lot for a tuner to run at any power into a
>>> non-resonant antenna and break a pile up.  :)
>>>
>>> You would actually have better success with a 12M dipole then trying
>>> to get
>>> a non-resonant beam to direct your signal.
>>>
>>> If I was in your shoes, I would quickly toss up a 12M dipole with some
>>> string and bubble gum as you would have a much higher radiated signal.
>>>
>>> Mike va3mw
>>>
>
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Re: KPA1500 RFI on 12m

Jim Brown-10
On 10/25/2019 2:01 PM, Bob McGraw K4TAX wrote:
> Except for my 6M yagi, all of my antennas are non-resonant antennas. My
> favorite is the 256 ft center fed wire {resonant at 1.825 MHz}  with a
> balanced feed.

Dean Straw, N6BV, retired editor of the ARRL Antenna Book and Antenna
Compendiums, is a very smart engineer and a very good friend. But his
promotion of this sort of antenna is probably the greatest error of his
time in that job, an idea whose time is LONG past, for many reasons.
Primary -- 1) it cannot be choked to kill noise on RX, and 99.9% of hams
live surrounded by local noise and 2) it's pattern is different on every
frequency.

I am a strong believer in resonant antennas for each band, if if the
must be multi-band antennas like fan dipoles to fit in the available
space. For example, a 20/15/10 fan fits in 33 ft and works great, with a
predictable pattern on each band. An 80/40 fan works on 15M, with a
predictable pattern on both 80 and 40. Hypower Antenna company sells
loaded antennas that are resonant on 80 and 40 and fit into about 100
ft; I used one in Chicago on 30 to great effect. All of these antennas
are fed with 50 or 75 ohm coax, and CAN be choked to kill RX noise.

RX noise is a VERY big deal -- if you can't hear 'em, you can't work
'em. If you haven't worked to minimize your RX noise, you're DXing with
one hand tied behind your back! My friend AG6EE goes to remote locations
in NV, OR, and CA to light up rare grids with 1kW on 6M. Folks trying to
work him complain of one-way propagation because he hears them really
well and the don't hear him, but the REAL problem is their local RX noise.

http://k9yc.com/KillingReceiveNoise.pdf  Text, NCJ article
http://k9yc.com/KillingRXNoiseVisalia.pdf  Slides Visalia talk

73, Jim K9YC
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Re: KPA1500 RFI on 12m

Eric Norris-2
In reply to this post by Dave wo2x
Yes, that is the solution.  But it shouldn't have to be for an amplifier of
the KPA1500's price and class.  Further testing shows that on other bands,
with an SWR of 1.5 to 2.0, if the tuner is IN, it also goes into random
retunes.  When the tuner is in BYPASS, the KPA1500 is happy.  Also very
weird.  I never had this problem with KAT500/KPA500 combo on the same
antennas, and still don't.  I think the KPA1500 firmware needs some
tweaking.  This is true even when running the KPA1500 at 500w

73 Eric WD6DBM

73 Eric WD6DBM

On Fri, Oct 25, 2019, 5:41 AM Dave <[hidden email]> wrote:

> In the KPA1500 utility I have the tuner bypassed for the whole 60 meter
> band. The tuner’s logic is detecting a high SWR and overriding the bypass
> selection. This happens at 30 watts forward power.
>
> The answer is to turn off the amp when on 60 and just use the radio’s
> tuner.
>
> Dave wo2x
>
> Sent from my waxed string and tin cans.
>
> > On Oct 25, 2019, at 8:17 AM, Andy Durbin <[hidden email]> wrote:
> >
> ______________________________________________________________
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RX noise and 2-wire lines (was: KPA1500 RFI on 12m)

Victor Rosenthal 4X6GP
In reply to this post by Jim Brown-10
Jim,

I have to disagree about balanced line. Unlike coax, both conductors are
exposed to external RF fields, so common mode noise will be rejected. If
the antenna and line are properly balanced (not always easy to do, I
admit) and if it is fed through a balanced antenna tuner, there is no
reason for it to be noisier than coax. Yes, it can't be choked, but it
doesn't need to be.

My antenna is a 10m long rotary dipole fed with open line. It has gone
through several iterations and I've been very careful to install the
line so that it is perpendicular to the antenna for as far as possible,
etc. I've tried various balun arrangements, but the system that works
best, both for reducing RF in the shack when transmitting and noise
immunity when receiving, is a Johnson kW Matchbox.

There is a building taller than mine a few hundred meters away from it,
and a very distinct noise peak when the antenna is turned toward it,
which seems to indicate that the noise is picked up by the antenna, not
the line. I notice the same noise peak with a coax-fed shielded loop
antenna, so it is definitely coming from the building, and isn't an
artifact of the alignment of the antenna to the line.  I am pretty sure
I have at least a 10 dB difference in noise when a band is open (at
least, when the antenna is not aimed at that building), but I will wait
until the band is solidly dead tonight to check that out.

My pattern is a form of figure 8 on 40-10 meters, but you are right that
you can't maintain the pattern over a greater frequency range.

My main point is that there is nothing inherently noisy about a two-wire
transmission line!

73,
Victor, 4X6GP
Rehovot, Israel
Formerly K2VCO
CWops no. 5
http://www.qsl.net/k2vco/
On 26-Oct-2019 10:32, Jim Brown wrote:

> On 10/25/2019 2:01 PM, Bob McGraw K4TAX wrote:
>> Except for my 6M yagi, all of my antennas are non-resonant antennas.
>> My favorite is the 256 ft center fed wire {resonant at 1.825 MHz}  
>> with a balanced feed.
>
> Dean Straw, N6BV, retired editor of the ARRL Antenna Book and Antenna
> Compendiums, is a very smart engineer and a very good friend. But his
> promotion of this sort of antenna is probably the greatest error of his
> time in that job, an idea whose time is LONG past, for many reasons.
> Primary -- 1) it cannot be choked to kill noise on RX, and 99.9% of hams
> live surrounded by local noise and 2) it's pattern is different on every
> frequency.
>
> I am a strong believer in resonant antennas for each band, if if the
> must be multi-band antennas like fan dipoles to fit in the available
> space. For example, a 20/15/10 fan fits in 33 ft and works great, with a
> predictable pattern on each band. An 80/40 fan works on 15M, with a
> predictable pattern on both 80 and 40. Hypower Antenna company sells
> loaded antennas that are resonant on 80 and 40 and fit into about 100
> ft; I used one in Chicago on 30 to great effect. All of these antennas
> are fed with 50 or 75 ohm coax, and CAN be choked to kill RX noise.
>
> RX noise is a VERY big deal -- if you can't hear 'em, you can't work
> 'em. If you haven't worked to minimize your RX noise, you're DXing with
> one hand tied behind your back! My friend AG6EE goes to remote locations
> in NV, OR, and CA to light up rare grids with 1kW on 6M. Folks trying to
> work him complain of one-way propagation because he hears them really
> well and the don't hear him, but the REAL problem is their local RX noise.
>
> http://k9yc.com/KillingReceiveNoise.pdf  Text, NCJ article
> http://k9yc.com/KillingRXNoiseVisalia.pdf  Slides Visalia talk
>
> 73, Jim K9YC

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Re: RX noise and 2-wire lines

Jim Brown-10
Vic,

What you're missing is that an antenna and its feedline are a SYSTEM,
and antennas can be unbalanced by their surroundings -- ground slope,
un-equal mounting heights, conductors in nearby buildings or structure,
trees, towers, etc. Any unbalance in the SYSTEM results in common mode
current on the feedline.

73, Jim K9YC

On 10/26/2019 7:11 AM, Victor Rosenthal 4X6GP wrote:
> I have to disagree about balanced line. Unlike coax, both conductors are
> exposed to external RF fields, so common mode noise will be rejected. If
> the antenna and line are properly balanced (not always easy to do, I
> admit) and if it is fed through a balanced antenna tuner, there is no
> reason for it to be noisier than coax. Yes, it can't be choked, but it
> doesn't need to be.

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Re: RX noise and 2-wire lines (was: KPA1500 RFI on 12m)

Lyn WØLEN
In reply to this post by Victor Rosenthal 4X6GP
Antennas are my passion.  In 50 years of hamming, I have probably experimented with virtually all variations of wire antennas.  My current antenna is far and away the best I have ever built.

Without going into all the details of my design considerations (location, regulations, budget, etc.) let me just list a few parameters that entered into my decision:

        1)  I have 400 feet of clear space behind my house, spanning an East - West direction.  I have trees located in usable locations, and the orientation of the house is workable.
        2)  I need to have a dependable 80m connection to our state capital, 275 miles to the South for EMCOMM purposes.
        3)  The antenna needs to provide good performance on all bands, 160 - 6m.
        4)  On all bands other than 80m I want multi-lobe radiation patterns to cover the entire US as well as acceptable worldwide coverage.
        5)  The antenna, while not necessarily needing to be "stealthy", needs to be unobtrusive from the street.

All this led me to building an Extended Double Zepp, cut for 3.5 MHz.  That's 360 feet long, center fed with 600 ohm "true ladder line."  The feedpoint of the ladder line is connected to a relatively short run of coax into the shack through a dual core hybrid balun (1:1 current and 4:1 voltage) which provides excellent RF choking as well as feedline isolation and very acceptable impedance matching for the KAT500.  The antenna is mounted about 30 feet above ground, which adds the NVIS capabilities I need on the lower bands.

The performance is everything I could ask for.  It gives me exactly the coverage I want in all respects with roughly 4 - 5 db increase in transmitted signal strength along with 4+ S-units decrease in noise level as compared to my previous antenna, a G5RV in an inverted "V" configuration.

Your mileage may vary, but for anyone looking to try something new (actually a very OLD design), it's a fun project.

73
Lyn, WØLEN


-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On Behalf Of Victor Rosenthal 4X6GP
Sent: Saturday, October 26, 2019 9:11 AM
To: [hidden email]
Subject: [Elecraft] RX noise and 2-wire lines (was: KPA1500 RFI on 12m)

Jim,

I have to disagree about balanced line. Unlike coax, both conductors are
exposed to external RF fields, so common mode noise will be rejected. If
the antenna and line are properly balanced (not always easy to do, I
admit) and if it is fed through a balanced antenna tuner, there is no
reason for it to be noisier than coax. Yes, it can't be choked, but it
doesn't need to be.

My antenna is a 10m long rotary dipole fed with open line. It has gone
through several iterations and I've been very careful to install the
line so that it is perpendicular to the antenna for as far as possible,
etc. I've tried various balun arrangements, but the system that works
best, both for reducing RF in the shack when transmitting and noise
immunity when receiving, is a Johnson kW Matchbox.

There is a building taller than mine a few hundred meters away from it,
and a very distinct noise peak when the antenna is turned toward it,
which seems to indicate that the noise is picked up by the antenna, not
the line. I notice the same noise peak with a coax-fed shielded loop
antenna, so it is definitely coming from the building, and isn't an
artifact of the alignment of the antenna to the line.  I am pretty sure
I have at least a 10 dB difference in noise when a band is open (at
least, when the antenna is not aimed at that building), but I will wait
until the band is solidly dead tonight to check that out.

My pattern is a form of figure 8 on 40-10 meters, but you are right that
you can't maintain the pattern over a greater frequency range.

My main point is that there is nothing inherently noisy about a two-wire
transmission line!

73,
Victor, 4X6GP
Rehovot, Israel
Formerly K2VCO
CWops no. 5
http://www.qsl.net/k2vco/
On 26-Oct-2019 10:32, Jim Brown wrote:

> On 10/25/2019 2:01 PM, Bob McGraw K4TAX wrote:
>> Except for my 6M yagi, all of my antennas are non-resonant antennas.
>> My favorite is the 256 ft center fed wire {resonant at 1.825 MHz}  
>> with a balanced feed.
>
> Dean Straw, N6BV, retired editor of the ARRL Antenna Book and Antenna
> Compendiums, is a very smart engineer and a very good friend. But his
> promotion of this sort of antenna is probably the greatest error of his
> time in that job, an idea whose time is LONG past, for many reasons.
> Primary -- 1) it cannot be choked to kill noise on RX, and 99.9% of hams
> live surrounded by local noise and 2) it's pattern is different on every
> frequency.
>
> I am a strong believer in resonant antennas for each band, if if the
> must be multi-band antennas like fan dipoles to fit in the available
> space. For example, a 20/15/10 fan fits in 33 ft and works great, with a
> predictable pattern on each band. An 80/40 fan works on 15M, with a
> predictable pattern on both 80 and 40. Hypower Antenna company sells
> loaded antennas that are resonant on 80 and 40 and fit into about 100
> ft; I used one in Chicago on 30 to great effect. All of these antennas
> are fed with 50 or 75 ohm coax, and CAN be choked to kill RX noise.
>
> RX noise is a VERY big deal -- if you can't hear 'em, you can't work
> 'em. If you haven't worked to minimize your RX noise, you're DXing with
> one hand tied behind your back! My friend AG6EE goes to remote locations
> in NV, OR, and CA to light up rare grids with 1kW on 6M. Folks trying to
> work him complain of one-way propagation because he hears them really
> well and the don't hear him, but the REAL problem is their local RX noise.
>
> http://k9yc.com/KillingReceiveNoise.pdf  Text, NCJ article
> http://k9yc.com/KillingRXNoiseVisalia.pdf  Slides Visalia talk
>
> 73, Jim K9YC

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