Urban stealth HF: Inside-the-backpack loop antenna?

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Re: Urban stealth HF: Inside-the-backpack loop antenna?

bill steffey
how about code to run a screwdriver ????antenna that is.

I use my k2 /kxpa100 in my VW   screwdriver up on the roof rack,.....
woeks great  but could be elecraftmatic !!!!

On 1/22/2019 10:56 PM, Wayne Burdick wrote:

> Thanks for the amazing response and great ideas.
>
> If someone wants to build a backpack loop antenna for 20 m sooner than I can, I promise to extensively field test it for you. If it works, it could become an Elecraft product. (AL1? :)
>
> The KXIO2 option for the KX2 includes two open-drain outputs that could be used to slew a C-tuning motor up and down with suitable buffering. I’ll write the code for that if/when it’s needed.
>
> Wayne
> N6KR
>
> ----
> elecraft.com
>
>> On Jan 22, 2019, at 7:43 PM, Bill Johnson <[hidden email]> wrote:
>>
>> The back pack frame would be the antenna?  Low power is the game.  I am not concerned. In the Vietnam era, I was in a station where we had ~5 10KW transmitters using wave guide at ~1.9Ghz and while there were very large dishes, the exposure was there.  I would never worry about HF at 10 watts close to my body, but there may be studies that dispute that.  I am still alive after 12 months constant exposure to agent orange.  No problem.  What was I writing about? :_)
>>
>> (Emoji added in case the sarcasm was missed.)
>>
>> 73,
>> Bill
>> K9YEQ
>>
>> https://wrj-tech.com/
>>
>> -----Original Message-----
>> From: [hidden email] <[hidden email]> On Behalf Of Wayne Burdick
>> Sent: Tuesday, January 22, 2019 2:57 PM
>> To: Elecraft <[hidden email]>
>> Cc: KX3 <[hidden email]>
>> Subject: [Elecraft] Urban stealth HF: Inside-the-backpack loop antenna?
>>
>> I’ve engaged in plenty of ultralight HF pack operation, with a KX2, AX1 antenna and a dragged counterpoise. In wide open spaces it’s a blast. But urban settings with dogs, wire-eating cacti and overzealous Neighborhood Watchers can distract from one’s radio experience.
>>
>> So, just for grins, I’d like to try something completely incognerdo: no visible antenna. A small remotely tuned loop (say 12” diameter) would seem to be the best choice, as it would fit entirely inside a small backpack. It could have  modest efficiency while not requiring a counterpoise wire. Rigid 1” copper pipe formed in a square would be convenient to deploy.
>>
>> The loop would be only 6 to 8” from soft tissue, so you’d want to run QRP, of course.  OTOH, we’re talking about HF. A cellphone by your ear is probably worse.
>>
>> Any other antenna suggestions?
>>
>> Wayne
>> N6KR
>>
>>
>>
>> ----
>> elecraft.com
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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>>
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>
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Re: Urban stealth HF: Inside-the-backpack loop antenna?

kd4iz
In reply to this post by David Gilbert
I love the AB7E concept...

Looks an awful lot like birth of a new character for cosplay and a Comicon run to me:
"EtherMan" - the RF belching steampunk simulacrum of an Isaac Asimov automaton! A little work with the 3D printer, an RPi with a 7" display, and some burnished 10 gauge wire coil gauntlets, chest shield flip down mount for the KX2. Ah the possibilities! KA6LMS doesn't stand a chance. Anyone want to give it a go?

Seriously now, has anyone looked at the rf field issues - ie the effect created by the position of the person (a 70% water, protein gel matrix) with the backpack on?

KD4IZ
Jack Spitznagel
FM19oo




-----Original Message-----
From: David Gilbert <[hidden email]>
Sent: Wednesday, January 23, 2019 00:04
To: [hidden email]
Subject: Re: [Elecraft] Urban stealth HF: Inside-the-backpack loop antenna?



Here's another idea.

Run a wire inside your shirt from one cuff across your back and down to the other cuff.  Wrap loading coils around each arm just above the elbow.  Feed the "dipole" in the center at the back of your neck.

I did a quick model (assuming your arms are held straight out) with 5.5 feet total length and 2200 inductive ohms for each coil, with each coil 30% from their respective ends of the wire.  It "resonates" at around
14.15 MHz, but with only about 0.4 ohms real feedpoint impedance.  I assume it would take some sort of extra matching network to bring that up enough that a KX2 with the internal tuner could drive it.

Ignoring the effect of a person's arm, another quick calculation says that the arm coils would need to be roughly 11 turns of 10 gauge wire
3.5 inches in diameter ... unless I made a mistake, which is quite possible.

It would bring new meaning to the term "compromise antenna", but I bet it would be more effective than a super small loop the size of backpack frame.

73,
Dave  AB7E



>
>
> On 1/22/19 12:57 PM, Wayne Burdick wrote:
>> I’ve engaged in plenty of ultralight HF pack operation, with a KX2,
>> AX1 antenna and a dragged counterpoise. In wide open spaces it’s a
>> blast. But urban settings with dogs, wire-eating cacti and
>> overzealous Neighborhood Watchers can distract from one’s radio
>> experience.
>>
>> So, just for grins, I’d like to try something completely incognerdo:
>> no visible antenna. A small remotely tuned loop (say 12” diameter)
>> would seem to be the best choice, as it would fit entirely inside a
>> small backpack. It could have  modest efficiency while not requiring
>> a counterpoise wire. Rigid 1” copper pipe formed in a square would be
>> convenient to deploy.
>>
>> The loop would be only 6 to 8” from soft tissue, so you’d want to run
>> QRP, of course.  OTOH, we’re talking about HF. A cellphone by your
>> ear is probably worse.
>>
>> Any other antenna suggestions?
>>
>> Wayne
>> N6KR



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Re: Urban stealth HF: Inside-the-backpack loop antenna?

K9FD
In reply to this post by wayne burdick
Years back QST had an article that showed a home made 2 meter "filter" made
in a garbage can,   they ran low power and placed a hot dog inside, 
closed the lid
and applied RF,   the hot dog was BBQed in short order,
Perhaps with QRP one could put a sandwhich in one pocket and coffee in
another
and while hiking to your destination you would have hot food and drink when
you arrived.
Not saying what may happen to the wienie of the person hiking. Your mileage
may vary as they say,  at least you wont have kids to tell the story to.

Merv K9FD

> Up the power to 100 W and you’ve got a personal heating appliance. Awesome.
>
> “Without RF, life itself would be impossible.”
>
> Wayne
>
>
> ----
> elecraft.com
>
>> On Jan 22, 2019, at 9:04 PM, David Gilbert <[hidden email]> wrote:
>>
>>
>>
>> Here's another idea.
>>
>> Run a wire inside your shirt from one cuff across your back and down to the other cuff.  Wrap loading coils around each arm just above the elbow.  Feed the "dipole" in the center at the back of your neck.
>>
>> I did a quick model (assuming your arms are held straight out) with 5.5 feet total length and 2200 inductive ohms for each coil, with each coil 30% from their respective ends of the wire.  It "resonates" at around 14.15 MHz, but with only about 0.4 ohms real feedpoint impedance.  I assume it would take some sort of extra matching network to bring that up enough that a KX2 with the internal tuner could drive it.
>>
>> Ignoring the effect of a person's arm, another quick calculation says that the arm coils would need to be roughly 11 turns of 10 gauge wire 3.5 inches in diameter ... unless I made a mistake, which is quite possible.
>>
>> It would bring new meaning to the term "compromise antenna", but I bet it would be more effective than a super small loop the size of backpack frame.
>>
>> 73,
>> Dave  AB7E
>>
>>
>>
>>>
>>>> On 1/22/19 12:57 PM, Wayne Burdick wrote:
>>>> I’ve engaged in plenty of ultralight HF pack operation, with a KX2, AX1 antenna and a dragged counterpoise. In wide open spaces it’s a blast. But urban settings with dogs, wire-eating cacti and overzealous Neighborhood Watchers can distract from one’s radio experience.
>>>>
>>>> So, just for grins, I’d like to try something completely incognerdo: no visible antenna. A small remotely tuned loop (say 12” diameter) would seem to be the best choice, as it would fit entirely inside a small backpack. It could have  modest efficiency while not requiring a counterpoise wire. Rigid 1” copper pipe formed in a square would be convenient to deploy.
>>>>
>>>> The loop would be only 6 to 8” from soft tissue, so you’d want to run QRP, of course.  OTOH, we’re talking about HF. A cellphone by your ear is probably worse.
>>>>
>>>> Any other antenna suggestions?
>>>>
>>>> Wayne
>>>> N6KR
>> ______________________________________________________________
>> 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
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> 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: [KX3] Urban stealth HF: Inside-the-backpack loop antenna?

wayne burdick
Administrator
In reply to this post by wayne burdick
Wish I had time to build one of these myself! A few other things in the queue....

Wayne
N6KR


> On Jan 23, 2019, at 6:32 AM, 'Dale Parfitt' [hidden email] [KX3] <[hidden email]> wrote:
>
>
> HI Wolf,
>
> VK3YE could have done so much better from an efficiency standpoint without making the loop any larger.
>
> 1. Flat metal stock is not as efficient as round stock (of the same circumference) because current crowding at the edges of the rectangular stock makes it appear smaller in surface area.
>
> 2. A much lower D capacitor such as a dual gang air variable with the gangs in series (to avoid resistive losses in the bearings) or  a butterfly would also have aided in  higher efficiency.
>
> 3. Copper would have helped efficiency  somewhat with its lower RF resistance and ability to be soldered  versus mechanical connections, but that is partially offset by aluminum’s larger skin depth. Of course copper is heavier and more expensive, but in tube form the weight issue could be minimized..
>
>  
>
> Just some thoughts. Again, the VK1OD calculator allows one to make precise efficiency measurements so even small improvements can be measured.  As an example, the difference in efficiency between using  braided coax as the loop radiator versus hardline or copper tubing is readily apparent. For the same diameter loop and same conductor diameter, a narrower bandwidth  means higher efficiency.
>
>  
>
> Dale W4OP
>
>  
>
> From: [hidden email] [mailto:[hidden email]] On Behalf Of 'Wolf Hoeller, OE7FTJ' wolf.oe7ftj@gmail..com [KX3]
> Sent: Wednesday, January 23, 2019 4:57 AM
> To: [hidden email]
> Subject: Fwd: [KX3] Urban stealth HF: Inside-the-backpack loop antenna?
>
>  
>
>  
>
> Wayne,
>
>  
>
> a really good idea.
>
> Have a look at VK3YE's youtube channel for his experiment to put a loop antenna in (frame of) a notebook bag. https://www.youtube.com/watch?v=BC5lFbLqaeg
>
>  
>
> Another good idea for a stealth antenna has the spain company Inac. Here is the suitcase with a loop inside the frame: https://www.inac-radio.com/MAK721PRO
>
>  
>
> I would like the idea, to sit in an urban park with my backpack or similar on my knees and make some contacts.
>
>
>
>
> Wolf, OE7FTJ
>
> Emergency Communications via Winlink Global Radio Email ®️
>
>  
>
>  
>
>  
>
> Am Di., 22. Jan. 2019 um 21:57 Uhr schrieb Wayne Burdick [hidden email] [KX3] <[hidden email]>:
>
>>  
>>
>> I’ve engaged in plenty of ultralight HF pack operation, with a KX2, AX1 antenna and a dragged counterpoise. In wide open spaces it’s a blast. But urban settings with dogs, wire-eating cacti and overzealous Neighborhood Watchers can distract from one’s radio experience.
>>
>>  
>>
>> So, just for grins, I’d like to try something completely incognerdo: no visible antenna. A small remotely tuned loop (say 12” diameter) would seem to be the best choice, as it would fit entirely inside a small backpack. It could have  modest efficiency while not requiring a counterpoise wire. Rigid 1” copper pipe formed in a square would be convenient to deploy.
>>
>>  
>>
>> The loop would be only 6 to 8” from soft tissue, so you’d want to run QRP, of course.  OTOH, we’re talking about HF. A cellphone by your ear is probably worse.
>>
>>  
>>
>> Any other antenna suggestions?
>>
>>  
>>
>> Wayne
>>
>> N6KR
>>
>>  
>>
>>  
>>
>
>
> __._,_.___
> Posted by: "Dale Parfitt" <[hidden email]>
> Reply via web post • Reply to sender • Reply to group • Start a New Topic • Messages in this topic (2)
>  
> Have you tried the highest rated email app?
> With 4.5 stars in iTunes, the Yahoo Mail app is the highest rated email app on the market. What are you waiting for? Now you can access all your inboxes (Gmail, Outlook, AOL and more) in one place. Never delete an email again with 1000GB of free cloud storage.
> VISIT YOUR GROUP
> • Privacy • Unsubscribe • Terms of Use
>
> SPONSORED LINKS
>
>
>
> .
>  
>
> __,_._,___

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Re: [KX3] Urban stealth HF: Inside-the-backpack loop antenna?

Jim AB3CV
I assume that this "backpack frame antenna" wouldn't be actually used when
being worn. The circulating currents in a Hi-Q loop result in strong RF
fields along the loop axis which should be avoided in use.

jim ab3cv

On Wed, Jan 23, 2019 at 11:21 AM Wayne Burdick <[hidden email]> wrote:

> Wish I had time to build one of these myself! A few other things in the
> queue....
>
> Wayne
> N6KR
>
>
> > On Jan 23, 2019, at 6:32 AM, 'Dale Parfitt' [hidden email] [KX3] <
> [hidden email]> wrote:
> >
> >
> > HI Wolf,
> >
> > VK3YE could have done so much better from an efficiency standpoint
> without making the loop any larger.
> >
> > 1. Flat metal stock is not as efficient as round stock (of the same
> circumference) because current crowding at the edges of the rectangular
> stock makes it appear smaller in surface area.
> >
> > 2. A much lower D capacitor such as a dual gang air variable with the
> gangs in series (to avoid resistive losses in the bearings) or  a butterfly
> would also have aided in  higher efficiency.
> >
> > 3. Copper would have helped efficiency  somewhat with its lower RF
> resistance and ability to be soldered  versus mechanical connections, but
> that is partially offset by aluminum’s larger skin depth. Of course copper
> is heavier and more expensive, but in tube form the weight issue could be
> minimized..
> >
> >
> >
> > Just some thoughts. Again, the VK1OD calculator allows one to make
> precise efficiency measurements so even small improvements can be
> measured.  As an example, the difference in efficiency between using
> braided coax as the loop radiator versus hardline or copper tubing is
> readily apparent. For the same diameter loop and same conductor diameter, a
> narrower bandwidth  means higher efficiency.
> >
> >
> >
> > Dale W4OP
> >
> >
> >
> > From: [hidden email] [mailto:[hidden email]] On Behalf Of
> 'Wolf Hoeller, OE7FTJ' wolf.oe7ftj@gmail..com [KX3]
> > Sent: Wednesday, January 23, 2019 4:57 AM
> > To: [hidden email]
> > Subject: Fwd: [KX3] Urban stealth HF: Inside-the-backpack loop antenna?
> >
> >
> >
> >
> >
> > Wayne,
> >
> >
> >
> > a really good idea.
> >
> > Have a look at VK3YE's youtube channel for his experiment to put a loop
> antenna in (frame of) a notebook bag.
> https://www.youtube.com/watch?v=BC5lFbLqaeg
> >
> >
> >
> > Another good idea for a stealth antenna has the spain company Inac. Here
> is the suitcase with a loop inside the frame:
> https://www.inac-radio.com/MAK721PRO
> >
> >
> >
> > I would like the idea, to sit in an urban park with my backpack or
> similar on my knees and make some contacts.
> >
> >
> >
> >
> > Wolf, OE7FTJ
> >
> > Emergency Communications via Winlink Global Radio Email ®️
> >
> >
> >
> >
> >
> >
> >
> > Am Di., 22. Jan. 2019 um 21:57 Uhr schrieb Wayne Burdick
> [hidden email] [KX3] <[hidden email]>:
> >
> >>
> >>
> >> I’ve engaged in plenty of ultralight HF pack operation, with a KX2, AX1
> antenna and a dragged counterpoise. In wide open spaces it’s a blast. But
> urban settings with dogs, wire-eating cacti and overzealous Neighborhood
> Watchers can distract from one’s radio experience.
> >>
> >>
> >>
> >> So, just for grins, I’d like to try something completely incognerdo: no
> visible antenna. A small remotely tuned loop (say 12” diameter) would seem
> to be the best choice, as it would fit entirely inside a small backpack. It
> could have  modest efficiency while not requiring a counterpoise wire.
> Rigid 1” copper pipe formed in a square would be convenient to deploy.
> >>
> >>
> >>
> >> The loop would be only 6 to 8” from soft tissue, so you’d want to run
> QRP, of course.  OTOH, we’re talking about HF. A cellphone by your ear is
> probably worse.
> >>
> >>
> >>
> >> Any other antenna suggestions?
> >>
> >>
> >>
> >> Wayne
> >>
> >> N6KR
> >>
> >>
> >>
> >>
> >>
> >
> >
> > __._,_.___
> > Posted by: "Dale Parfitt" <[hidden email]>
> > Reply via web post    •       Reply to sender         •       Reply to
> group  •       Start a New Topic       •       Messages in this topic (2)
> >
> > Have you tried the highest rated email app?
> > With 4.5 stars in iTunes, the Yahoo Mail app is the highest rated email
> app on the market. What are you waiting for? Now you can access all your
> inboxes (Gmail, Outlook, AOL and more) in one place. Never delete an email
> again with 1000GB of free cloud storage.
> > VISIT YOUR GROUP
> > • Privacy • Unsubscribe • Terms of Use
> >
> > SPONSORED LINKS
> >
> >
> >
> > .
> >
> >
> > __,_._,___
>
> ______________________________________________________________
> 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: [KX3] Urban stealth HF: Inside-the-backpack loop antenna?

wayne burdick
Administrator
The entire purpose of the exercise is to be able to operate while walking. If the field is a potential health risk, power would have to be dropped accordingly.

Wayne


> On Jan 23, 2019, at 8:28 AM, Jim Miller <[hidden email]> wrote:
>
> I assume that this "backpack frame antenna" wouldn't be actually used when being worn. The circulating currents in a Hi-Q loop result in strong RF fields along the loop axis which should be avoided in use.
>
> jim ab3cv
>
> On Wed, Jan 23, 2019 at 11:21 AM Wayne Burdick <[hidden email]> wrote:
> Wish I had time to build one of these myself! A few other things in the queue....
>
> Wayne
> N6KR
>
>
> > On Jan 23, 2019, at 6:32 AM, 'Dale Parfitt' [hidden email] [KX3] <[hidden email]> wrote:
> >
> >
> > HI Wolf,
> >
> > VK3YE could have done so much better from an efficiency standpoint without making the loop any larger.
> >
> > 1. Flat metal stock is not as efficient as round stock (of the same circumference) because current crowding at the edges of the rectangular stock makes it appear smaller in surface area.
> >
> > 2. A much lower D capacitor such as a dual gang air variable with the gangs in series (to avoid resistive losses in the bearings) or  a butterfly would also have aided in  higher efficiency.
> >
> > 3. Copper would have helped efficiency  somewhat with its lower RF resistance and ability to be soldered  versus mechanical connections, but that is partially offset by aluminum’s larger skin depth. Of course copper is heavier and more expensive, but in tube form the weight issue could be minimized..
> >
> >  
> >
> > Just some thoughts. Again, the VK1OD calculator allows one to make precise efficiency measurements so even small improvements can be measured.  As an example, the difference in efficiency between using  braided coax as the loop radiator versus hardline or copper tubing is readily apparent. For the same diameter loop and same conductor diameter, a narrower bandwidth  means higher efficiency.
> >
> >  
> >
> > Dale W4OP
> >
> >  
> >
> > From: [hidden email] [mailto:[hidden email]] On Behalf Of 'Wolf Hoeller, OE7FTJ' wolf.oe7ftj@gmail..com [KX3]
> > Sent: Wednesday, January 23, 2019 4:57 AM
> > To: [hidden email]
> > Subject: Fwd: [KX3] Urban stealth HF: Inside-the-backpack loop antenna?
> >
> >  
> >
> >  
> >
> > Wayne,
> >
> >  
> >
> > a really good idea.
> >
> > Have a look at VK3YE's youtube channel for his experiment to put a loop antenna in (frame of) a notebook bag. https://www.youtube.com/watch?v=BC5lFbLqaeg
> >
> >  
> >
> > Another good idea for a stealth antenna has the spain company Inac. Here is the suitcase with a loop inside the frame: https://www.inac-radio.com/MAK721PRO
> >
> >  
> >
> > I would like the idea, to sit in an urban park with my backpack or similar on my knees and make some contacts.
> >
> >
> >
> >
> > Wolf, OE7FTJ
> >
> > Emergency Communications via Winlink Global Radio Email ®️
> >
> >  
> >
> >  
> >
> >  
> >
> > Am Di., 22. Jan. 2019 um 21:57 Uhr schrieb Wayne Burdick [hidden email] [KX3] <[hidden email]>:
> >
> >>  
> >>
> >> I’ve engaged in plenty of ultralight HF pack operation, with a KX2, AX1 antenna and a dragged counterpoise. In wide open spaces it’s a blast. But urban settings with dogs, wire-eating cacti and overzealous Neighborhood Watchers can distract from one’s radio experience.
> >>
> >>  
> >>
> >> So, just for grins, I’d like to try something completely incognerdo: no visible antenna. A small remotely tuned loop (say 12” diameter) would seem to be the best choice, as it would fit entirely inside a small backpack. It could have  modest efficiency while not requiring a counterpoise wire. Rigid 1” copper pipe formed in a square would be convenient to deploy.
> >>
> >>  
> >>
> >> The loop would be only 6 to 8” from soft tissue, so you’d want to run QRP, of course.  OTOH, we’re talking about HF. A cellphone by your ear is probably worse.
> >>
> >>  
> >>
> >> Any other antenna suggestions?
> >>
> >>  
> >>
> >> Wayne
> >>
> >> N6KR
> >>
> >>  
> >>
> >>  
> >>
> >
> >
> > __._,_.___
> > Posted by: "Dale Parfitt" <[hidden email]>
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Re: Urban stealth HF: Inside-the-backpack loop antenna?

Dave New, N8SBE
In reply to this post by wayne burdick
The loop would be only 6 to 8” from soft tissue, so you’d want to
run QRP, of course. OTOH, we’re talking about HF. A cellphone by your
ear is probably worse.

Any other antenna suggestions?

Wayne
N6KR

Who was that guy at the HFPack get-together at HARA a few Daytons ago,
that was running A KILOWATT pedestrian mobile?  It he still on this
planet? :-)

73.

-- Dave, N8SBE
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Re: Urban stealth HF: Inside-the-backpack loop antenna?

Dave New, N8SBE
In reply to this post by wayne burdick

> Here's another idea.
>
> Run a wire inside your shirt from one cuff across your back and down to
> the other cuff.  Wrap loading coils around each arm just above the
> elbow.  Feed the "dipole" in the center at the back of your neck.
>
> I did a quick model (assuming your arms are held straight out) with 5.5
> feet total length and 2200 inductive ohms for each coil, with each coil
> 30% from their respective ends of the wire.  It "resonates" at around
> 14.15 MHz, but with only about 0.4 ohms real feedpoint impedance.  I
> assume it would take some sort of extra matching network to bring that
> up enough that a KX2 with the internal tuner could drive it.
>
> Ignoring the effect of a person's arm, another quick calculation says
> that the arm coils would need to be roughly 11 turns of 10 gauge wire
> 3.5 inches in diameter ... unless I made a mistake, which is quite
> possible.
>
> It would bring new meaning to the term "compromise antenna", but I bet
> it would be more effective than a super small loop the size of backpack
> frame.
>
> 73,
> Dave  AB7E

Wouldn't that be a 'scarecrow' antenna?

73,

-- Dave, N8SBE


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Re: Urban stealth HF: Inside-the-backpack loop antenna?

Paul Wilton-2
In reply to this post by wayne burdick
10+ years ago, we built a HF loop inside a coat.  I can’t really tell you the application but the loop was made of copper braid and put between the liner and the outer shell of the coat.  It was tuned with a simple L match with a LED to indicate peak power.  We operated it on the 80, 60 and 40m bands.  The drive was an FT817 at 5w.

We weren’t trying for DX but it worked well for the short distances we needed it to work.  It was also pretty easy to tune up and and once tuned stayed there.

73


Paul
M1CNK





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Re: [KX3] Urban stealth HF: Inside-the-backpack loop antenna?

Mike Cox
In reply to this post by wayne burdick
A proper shield of a KPA-1500/PS with battery and 240VAC inverter should
be adequate protection if stuffed between the antenna and your backside ;-).

... Mike

On 1/23/2019 11:34 AM, Wayne Burdick wrote:

> The entire purpose of the exercise is to be able to operate while walking. If the field is a potential health risk, power would have to be dropped accordingly.
>
> Wayne
>
>
>> On Jan 23, 2019, at 8:28 AM, Jim Miller <[hidden email]> wrote:
>>
>> I assume that this "backpack frame antenna" wouldn't be actually used when being worn. The circulating currents in a Hi-Q loop result in strong RF fields along the loop axis which should be avoided in use.
>>
>> jim ab3cv
>>
>> On Wed, Jan 23, 2019 at 11:21 AM Wayne Burdick <[hidden email]> wrote:
>> Wish I had time to build one of these myself! A few other things in the queue....
>>
>> Wayne
>> N6KR
>>
>>
>>> On Jan 23, 2019, at 6:32 AM, 'Dale Parfitt' [hidden email] [KX3] <[hidden email]> wrote:
>>>
>>>
>>> HI Wolf,
>>>
>>> VK3YE could have done so much better from an efficiency standpoint without making the loop any larger.
>>>
>>> 1. Flat metal stock is not as efficient as round stock (of the same circumference) because current crowding at the edges of the rectangular stock makes it appear smaller in surface area.
>>>
>>> 2. A much lower D capacitor such as a dual gang air variable with the gangs in series (to avoid resistive losses in the bearings) or  a butterfly would also have aided in  higher efficiency.
>>>
>>> 3. Copper would have helped efficiency  somewhat with its lower RF resistance and ability to be soldered  versus mechanical connections, but that is partially offset by aluminum’s larger skin depth. Of course copper is heavier and more expensive, but in tube form the weight issue could be minimized..
>>>
>>>  
>>>
>>> Just some thoughts. Again, the VK1OD calculator allows one to make precise efficiency measurements so even small improvements can be measured.  As an example, the difference in efficiency between using  braided coax as the loop radiator versus hardline or copper tubing is readily apparent. For the same diameter loop and same conductor diameter, a narrower bandwidth  means higher efficiency.
>>>
>>>  
>>>
>>> Dale W4OP
>>>
>>>  
>>>
>>> From: [hidden email] [mailto:[hidden email]] On Behalf Of 'Wolf Hoeller, OE7FTJ' wolf.oe7ftj@gmail..com [KX3]
>>> Sent: Wednesday, January 23, 2019 4:57 AM
>>> To: [hidden email]
>>> Subject: Fwd: [KX3] Urban stealth HF: Inside-the-backpack loop antenna?
>>>
>>>  
>>>
>>>    
>>>
>>> Wayne,
>>>
>>>  
>>>
>>> a really good idea.
>>>
>>> Have a look at VK3YE's youtube channel for his experiment to put a loop antenna in (frame of) a notebook bag. https://www.youtube.com/watch?v=BC5lFbLqaeg
>>>
>>>  
>>>
>>> Another good idea for a stealth antenna has the spain company Inac. Here is the suitcase with a loop inside the frame: https://www.inac-radio.com/MAK721PRO
>>>
>>>  
>>>
>>> I would like the idea, to sit in an urban park with my backpack or similar on my knees and make some contacts.
>>>
>>>
>>>
>>>
>>> Wolf, OE7FTJ
>>>
>>> Emergency Communications via Winlink Global Radio Email ®️
>>>
>>>  
>>>
>>>  
>>>
>>>  
>>>
>>> Am Di., 22. Jan. 2019 um 21:57 Uhr schrieb Wayne Burdick [hidden email] [KX3] <[hidden email]>:
>>>
>>>>    
>>>>
>>>> I’ve engaged in plenty of ultralight HF pack operation, with a KX2, AX1 antenna and a dragged counterpoise. In wide open spaces it’s a blast. But urban settings with dogs, wire-eating cacti and overzealous Neighborhood Watchers can distract from one’s radio experience.
>>>>
>>>>  
>>>>
>>>> So, just for grins, I’d like to try something completely incognerdo: no visible antenna. A small remotely tuned loop (say 12” diameter) would seem to be the best choice, as it would fit entirely inside a small backpack. It could have  modest efficiency while not requiring a counterpoise wire. Rigid 1” copper pipe formed in a square would be convenient to deploy.
>>>>
>>>>  
>>>>
>>>> The loop would be only 6 to 8” from soft tissue, so you’d want to run QRP, of course.  OTOH, we’re talking about HF. A cellphone by your ear is probably worse.
>>>>
>>>>  
>>>>
>>>> Any other antenna suggestions?
>>>>
>>>>  
>>>>
>>>> Wayne
>>>>
>>>> N6KR
>>>>
>>>>  
>>>>
>>>>  
>>>>
>>>
>>> __._,_.___
>>> Posted by: "Dale Parfitt" <[hidden email]>
>>> Reply via web post    •       Reply to sender         •       Reply to group  •       Start a New Topic       •       Messages in this topic (2)
>>>  
>>> Have you tried the highest rated email app?
>>> With 4.5 stars in iTunes, the Yahoo Mail app is the highest rated email app on the market. What are you waiting for? Now you can access all your inboxes (Gmail, Outlook, AOL and more) in one place. Never delete an email again with 1000GB of free cloud storage.
>>> VISIT YOUR GROUP
>>> • Privacy • Unsubscribe • Terms of Use
>>>
>>> SPONSORED LINKS
>>>
>>>
>>>
>>> .
>>>  
>>>
>>> __,_._,___
>> ______________________________________________________________
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Not built 40/20 K1 Kit

Bob W7AVK-2
In reply to this post by Dave New, N8SBE
.In 2000 I purchased for a high school friend a two band [40 and 20]  K1
kit.  Idea was to kick start his interest in ham radio. Turned out he
put the kit away and never returned to ham radio.

Anyone interested in a 40 and 20 meter original K1 kit in the original
box and packaging?

73  Bob  W7AVK



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Re: Urban stealth HF: Inside-the-backpack loop antenna?

Elecraft mailing list
In reply to this post by Dave New, N8SBE

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Re: Urban stealth HF: Inside-the-backpack loop antenna?

Elecraft mailing list

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Re: [KX3] Urban stealth HF: Inside-the-backpack loop antenna?

wayne burdick
Administrator
In reply to this post by wayne burdick
That might fit. Maybe something a little shorter, say 18".

Can it be used with just 2 feet of coax? What's the bandwidth? How does it compare to a 3' loop or a 4' whip?

Wayne
N6KR


> On Jan 23, 2019, at 9:51 AM, Jeff Wagner <[hidden email]> wrote:
>
> See the picture of a 20 Meter EH antenna on my QRZ page https://www.qrz.com/db/KK6CUG.
>
> It would fit into a backpack but it's 20 M only. Beer bottle for scale only - hi hi.
>
> https://www.qrz.com/db/KK6CUG
>
> Jeff, KK6CUG
>
> On 1/23/2019 8:34, Wayne Burdick [hidden email] [KX3] wrote:
>> The entire purpose of the exercise is to be able to operate while walking. If the field is a potential health risk, power would have to be dropped accordingly.
>>
>> Wayne
>>
>> > On Jan 23, 2019, at 8:28 AM, Jim Miller <[hidden email]> wrote:
>> >
>> > I assume that this "backpack frame antenna" wouldn't be actually used when being worn. The circulating currents in a Hi-Q loop result in strong RF fields along the loop axis which should be avoided in use.
>> >
>> > jim ab3cv
>> >
>>
>
>
>
>
>
>
>
>
>
>
>> > On Wed, Jan 23, 2019 at 11:21 AM Wayne Burdick <[hidden email]> wrote:
>> > Wish I had time to build one of these myself! A few other things in the queue....
>> >
>> > Wayne
>> > N6KR
>> >
>> >
>> > > On Jan 23, 2019, at 6:32 AM, 'Dale Parfitt' [hidden email] [KX3] <[hidden email]> wrote:
>> > >
>> > >
>> > > HI Wolf,
>> > >
>> > > VK3YE could have done so much better from an efficiency standpoint without making the loop any larger.
>> > >
>> > > 1. Flat metal stock is not as efficient as round stock (of the same circumference) because current crowding at the edges of the rectangular stock makes it appear smaller in surface area.
>> > >
>> > > 2. A much lower D capacitor such as a dual gang air variable with the gangs in series (to avoid resistive losses in the bearings) or a butterfly would also have aided in higher efficiency.
>> > >
>> > > 3. Copper would have helped efficiency somewhat with its lower RF resistance and ability to be soldered versus mechanical connections, but that is partially offset by aluminum’s larger skin depth. Of course copper is heavier and more expensive, but in tube form the weight issue could be minimized..
>> > >
>> > >
>> > >
>> > > Just some thoughts. Again, the VK1OD calculator allows one to make precise efficiency measurements so even small improvements can be measured. As an example, the difference in efficiency between using braided coax as the loop radiator versus hardline or copper tubing is readily apparent. For the same diameter loop and same conductor diameter, a narrower bandwidth means higher efficiency.
>> > >
>> > >
>> > >
>> > > Dale W4OP
>> > >
>> > >
>> > >
>> > > From: [hidden email] [mailto:[hidden email]] On Behalf Of 'Wolf Hoeller, OE7FTJ' wolf.oe7ftj@gmail..com [KX3]
>> > > Sent: Wednesday, January 23, 2019 4:57 AM
>> > > To: [hidden email]
>> > > Subject: Fwd: [KX3] Urban stealth HF: Inside-the-backpack loop antenna?
>> > >
>> > >
>> > >
>> > >
>> > >
>> > > Wayne,
>> > >
>> > >
>> > >
>> > > a really good idea.
>> > >
>> > > Have a look at VK3YE's youtube channel for his experiment to put a loop antenna in (frame of) a notebook bag. https://www.youtube.com/watch?v=BC5lFbLqaeg
>> > >
>> > >
>> > >
>> > > Another good idea for a stealth antenna has the spain company Inac. Here is the suitcase with a loop inside the frame: https://www.inac-radio.com/MAK721PRO
>> > >
>> > >
>> > >
>> > > I would like the idea, to sit in an urban park with my backpack or similar on my knees and make some contacts.
>> > >
>> > >
>> > >
>> > >
>> > > Wolf, OE7FTJ
>> > >
>> > > Emergency Communications via Winlink Global Radio Email ®️
>> > >
>> > >
>> > >
>> > >
>> > >
>> > >
>> > >
>> > > Am Di., 22. Jan. 2019 um 21:57 Uhr schrieb Wayne Burdick [hidden email] [KX3] <[hidden email]>:
>> > >
>> > >>
>> > >>
>> > >> I’ve engaged in plenty of ultralight HF pack operation, with a KX2, AX1 antenna and a dragged counterpoise. In wide open spaces it’s a blast. But urban settings with dogs, wire-eating cacti and overzealous Neighborhood Watchers can distract from one’s radio experience.
>> > >>
>> > >>
>> > >>
>> > >> So, just for grins, I’d like to try something completely incognerdo: no visible antenna. A small remotely tuned loop (say 12” diameter) would seem to be the best choice, as it would fit entirely inside a small backpack. It could have modest efficiency while not requiring a counterpoise wire. Rigid 1” copper pipe formed in a square would be convenient to deploy.
>> > >>
>> > >>
>> > >>
>> > >> The loop would be only 6 to 8” from soft tissue, so you’d want to run QRP, of course. OTOH, we’re talking about HF. A cellphone by your ear is probably worse.
>> > >>
>> > >>
>> > >>
>> > >> Any other antenna suggestions?
>> > >>
>> > >>
>> > >>
>> > >> Wayne
>> > >>
>> > >> N6KR
>> > >>
>> > >>
>> > >>
>> > >>
>> > >>
>> > >
>> > >
>> > >
>> >
>> > __________________________________________________________
>> > 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]
>>
>>
>> __._,_.___
>> Posted by: Wayne Burdick <[hidden email]>
>> Reply via web post • Reply to sender • Reply to group • Start a New Topic • Messages in this topic (1)
>>  
>> Have you tried the highest rated email app?
>> With 4.5 stars in iTunes, the Yahoo Mail app is the highest rated email app on the market. What are you waiting for? Now you can access all your inboxes (Gmail, Outlook, AOL and more) in one place. Never delete an email again with 1000GB of free cloud storage.
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> --
> Jeff
>

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Re: [KX3] Urban stealth HF: Inside-the-backpack loop antenna?

Grant Youngman-2
It might be useful to read W8JI’s take on the E/H antenna … https://www.w8ji.com/e-h_antenna.htm <https://www.w8ji.com/e-h_antenna.htm>

Grant NQ5T
K3 #2091 KX3 #8342

> On Jan 23, 2019, at 10:07 PM, Wayne Burdick <[hidden email]> wrote:
>
> That might fit. Maybe something a little shorter, say 18".
>
> Can it be used with just 2 feet of coax? What's the bandwidth? How does it compare to a 3' loop or a 4' whip?
>
> Wayne
> N6KR
>
>

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Re: [KX3] Urban stealth HF: Inside-the-backpack loop antenna?

Jim Shepherd
In reply to this post by wayne burdick
Cut a large double sided piece of double sided circuit board to fit the
backpack.
Etch the back side with a symmetric Hilbert curve split into 2 columns fed
at the bottom center and the two columns attached at the top.  Leave the
other side as a solid ground plane... It will take some work to make a
matching network, but the length of the 'curve' can easily be a half wave
on 20 meters. It will be directional to your rear as you walk along.

Jim W6US
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Re: Urban stealth HF: Inside-the-backpack loop antenna?

Leroy Buller
In reply to this post by wayne burdick
When I was in College at Kansas State, I had a random length long wire out
the window and up into some trees from the basement apartment.   I used a
simple coil and cap with alligator clips to make a LCD tuner on a piece of
pine.  What made it work was the copper pipe water inlet two feet from the
OP desk.  Good ground.   I worked 80 through 10 with my HW100.  No one
never saw the antenna in 5 years.  BS and Masters

Lee K0WA

On Tue, Jan 22, 2019, 2:57 PM Wayne Burdick <[hidden email] wrote:

> I’ve engaged in plenty of ultralight HF pack operation, with a KX2, AX1
> antenna and a dragged counterpoise. In wide open spaces it’s a blast. But
> urban settings with dogs, wire-eating cacti and overzealous Neighborhood
> Watchers can distract from one’s radio experience.
>
> So, just for grins, I’d like to try something completely incognerdo: no
> visible antenna. A small remotely tuned loop (say 12” diameter) would seem
> to be the best choice, as it would fit entirely inside a small backpack. It
> could have  modest efficiency while not requiring a counterpoise wire.
> Rigid 1” copper pipe formed in a square would be convenient to deploy.
>
> The loop would be only 6 to 8” from soft tissue, so you’d want to run QRP,
> of course.  OTOH, we’re talking about HF. A cellphone by your ear is
> probably worse.
>
> Any other antenna suggestions?
>
> Wayne
> N6KR
>
>
>
> ----
> elecraft.com
> ______________________________________________________________
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Re: [KX3] Urban stealth HF: Inside-the-backpack loop antenna?

Gwen Patton
In reply to this post by Jim Shepherd
>
> Jim Said: Cut a large double sided piece of double sided circuit board to
> fit the
> backpack. Etch the back side with a symmetric Hilbert curve split into 2
> columns fed
> at the bottom center and the two columns attached at the top.


 Just don't accidentally etch a Do-Nha curve, or you might wind up with a
summoning grid that attracts alien monstrosities from beyond spacetime
that'll eat your brain. hi hi

73,
Gwen, NG3P

(In reference to this:
http://radiopsychedelica.blogspot.com/2014/01/dho-na-curve-of-sleeper.html)

On Thu, Jan 24, 2019 at 1:37 AM Jim Shepherd <[hidden email]> wrote:

> Cut a large double sided piece of double sided circuit board to fit the
> backpack.
> Etch the back side with a symmetric Hilbert curve split into 2 columns fed
> at the bottom center and the two columns attached at the top.  Leave the
> other side as a solid ground plane... It will take some work to make a
> matching network, but the length of the 'curve' can easily be a half wave
> on 20 meters. It will be directional to your rear as you walk along.
>
> Jim W6US
> ______________________________________________________________
> Elecraft mailing list
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> Message delivered to [hidden email]
>


--

-+-+-+-+-
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http://quarktime.net
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Re: Not built 40/20 K1 Kit

Ken Schillinger
In reply to this post by Bob W7AVK-2
Bob,I haven't heard from you, so I'll assume there's an email issue. What is your asking price?Please reply to [hidden email],  Ken ke7hge


Sent from my Galaxy Tab® E
-------- Original message --------From: Bob W7AVK <[hidden email]> Date: 1/23/19  1:43 PM  (GMT-08:00) To: [hidden email] Subject: [Elecraft] Not built 40/20 K1 Kit
.In 2000 I purchased for a high school friend a two band [40 and 20]  K1
kit.  Idea was to kick start his interest in ham radio. Turned out he
put the kit away and never returned to ham radio.

Anyone interested in a 40 and 20 meter original K1 kit in the original
box and packaging?

73  Bob  W7AVK



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