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

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

wayne burdick
Administrator
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: [KX3] Urban stealth HF: Inside-the-backpack loop antenna?

Mark Goldberg
I would expect any high Q antenna like a loop would be detuned by any
movement or any metal you pass by. One more reason to support automatic
mobile screwdriver / mag loop antenna tuning on the KX series.
A flag on a backpack would be more or less ignored. Just put a flag on the
top of the AX1. Counterpoise is an issue though. Maybe a short one down
your leg?

Now, if you dressed as a homeless or otherwise distressed person, lots of
weird things are possible, tinfoil hat with a big flag, dragged wire
disguised as one of those fake animals on a leash, etc. The weirder, the
more people will ignore you.

Hopefully taken in the spirit of which it is posted.

73,

Mark
W7MLG


On Tue, Jan 22, 2019 at 1:57 PM Wayne Burdick [hidden email] [KX3] <
[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: Urban stealth HF: Inside-the-backpack loop antenna?

Steve Sergeant
In reply to this post by wayne burdick
On 1/22/19 12:57 PM, Wayne Burdick wrote:
>  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.

[Deletia]

> Any other antenna suggestions?

I tried a 52ft 26ga wire J-pole/Zep on the line of a 5ft parafoil kite,
with 50ft of kite line above the antenna, and another 50' of RG-174
between the antenna and the radio.

I'll grant that this is not as invisible as your idea. But I felt
reasonably inconspicuous working SSB with cell-phone type earbuds
(w/mic), and the KX2 in an open waist-pack, out in an open field of a
large city park. People just thought I was on a phone call while flying
the kite. It helped that there were several other kite-fliers in the
park that day.

It was not a particularly good day for propagation, but I did work Las
Vegas and Spokane from Silicon Valley with under 10W on 20m.


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

Elecraft mailing list
In reply to this post by Mark Goldberg
Mark (W7MLG),  It is scary how perfectly sane and normal your suggestions sound to me :)

Very 73 - Mike - K9JRI







> On Jan 22, 2019, at 4:32 PM, Mark Goldberg <[hidden email]> wrote:
>
> I would expect any high Q antenna like a loop would be detuned by any
> movement or any metal you pass by. One more reason to support automatic
> mobile screwdriver / mag loop antenna tuning on the KX series.
> A flag on a backpack would be more or less ignored. Just put a flag on the
> top of the AX1. Counterpoise is an issue though. Maybe a short one down
> your leg?
>
> Now, if you dressed as a homeless or otherwise distressed person, lots of
> weird things are possible, tinfoil hat with a big flag, dragged wire
> disguised as one of those fake animals on a leash, etc. The weirder, the
> more people will ignore you.
>
> Hopefully taken in the spirit of which it is posted.
>
> 73,
>
> Mark
> W7MLG
>
>
> On Tue, Jan 22, 2019 at 1:57 PM Wayne Burdick [hidden email] [KX3] <
> [hidden email]> wrote:
>

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

Grant Youngman-2
In reply to this post by wayne burdick
The problem is loop diameter.  Efficiency on 20m of a 12” diameter loop would be on the order of 5%. Forget it entirely on 40m .. essentially a dummy load that would take around 1200 pf to resonate. On 17m efficiency would go up to around 11%.

I use a loop portable all the time (Alexloop, W4OP) and they work well. They’re both about 3 ft in diameter. The Alexloop is light enough to be carried around hand held ... the W4OP needs a table top or tripod.

Grant NQ5T

Sent from my iPhone

> On Jan 22, 2019, at 3:57 PM, Wayne Burdick <[hidden email]> wrote:
>
>
>
> 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
>
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Re: Urban stealth HF: Inside-the-backpack loop antenna?

K9MA
On 1/22/2019 15:46, Grant Youngman wrote:
> The problem is loop diameter.

It doesn't have to be round.

73,

Scott K9MA


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

Clay Autery-2
In reply to this post by wayne burdick
Consider integrating the loop into a purpose built/modified backpack...  or the frame.
You can get a larger enclosed area, maintain easier use of the pack's volume without jacking up the loop, and better insure the loop geometry doesn't change as you pack/move/use it.
With a little creativity, yiu could also integrate some variable tuning into the design with access by hand if you place the adjusrable parts in the right location...
If you do switch in/out parts, it could be just a switch setup on the torso strap...
If QRP, I'd try to use the frame or an extension thereof...
Even the flexible plastic stiffeners in some frames could be used to carry a loop wire.
Good luck!
73,
ClayKY5G


Sent from my Verizon, Samsung Galaxy smartphone
-------- Original message --------From: Wayne Burdick <[hidden email]> Date: 1/22/19  14:57  (GMT-06:00) 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



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

Grant Youngman-2
In reply to this post by K9MA
Yes, it does not have to be round.  The actual measurement of interest is Circumference of whatever shape it is (e.g, the total length of the radiator).  A 12” loop or square, or whatever,  is still going to have a very low efficiency at this size point.  But closer to rounder is better …

Grant NQ5T
K3 #2091 KX3 #8342

> On Jan 22, 2019, at 4:51 PM, K9MA <[hidden email]> wrote:
>
> On 1/22/2019 15:46, Grant Youngman wrote:
>> The problem is loop diameter.
>
> It doesn't have to be round.
>
> 73,
>
> Scott K9MA
>
>
> --

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

K9MA
There's undoubtedly a trade-off between rounder and longer. I was
thinking of a typical more or less rectangular backpack, which would
have a circumference much larger than a 12 inch circle. A typical
backpacking pack could accommodate a circumference of about 88 inches,
more than twice that of a 12 inch round loop. Granted, such a large pack
wouldn't exactly be inconspicuous on an urban hiking trail, but you
could always put some rocks in it, and pretend you're training for a
Grand Canyon hike.

73,
Scott K9MA

On 1/22/2019 16:09, Grant Youngman wrote:

> Yes, it does not have to be round.  The actual measurement of interest
> is Circumference of whatever shape it is (e.g, the total length of the
> radiator).  A 12” loop or square, or whatever,  is still going to have
> a very low efficiency at this size point.  But closer to rounder is
> better …
>
> Grant NQ5T
> K3 #2091 KX3 #8342
>
>> On Jan 22, 2019, at 4:51 PM, K9MA <[hidden email]
>> <mailto:[hidden email]>> wrote:
>>
>> On 1/22/2019 15:46, Grant Youngman wrote:
>>> The problem is loop diameter.
>>
>> It doesn't have to be round.
>>
>> 73,
>>
>> Scott K9MA
>>
>>
>> --
>

--
Scott  K9MA

[hidden email]

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

turnbull
In reply to this post by Grant Youngman-2
Why not a collapsible Alexloop mag loop which fits in your back pack and will be nore efficient.    73 Doug EI2CN


Sent from my Samsung Galaxy smartphone.
-------- Original message --------From: Grant Youngman <[hidden email]> Date: 22/01/2019  22:09  (GMT+00:00) To: K9MA <[hidden email]> Cc: [hidden email] Subject: Re: [Elecraft] Urban stealth HF: Inside-the-backpack loop antenna?
Yes, it does not have to be round.  The actual measurement of interest is Circumference of whatever shape it is (e.g, the total length of the radiator).  A 12” loop or square, or whatever,  is still going to have a very low efficiency at this size point.  But closer to rounder is better …

Grant NQ5T
K3 #2091 KX3 #8342

> On Jan 22, 2019, at 4:51 PM, K9MA <[hidden email]> wrote:
>
> On 1/22/2019 15:46, Grant Youngman wrote:
>> The problem is loop diameter.
>
> It doesn't have to be round.
>
> 73,
>
> Scott K9MA
>
>
> --

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Ferrite Rod? (was: Urban stealth HF...)

Steve Sergeant
In reply to this post by wayne burdick
Just as a way-out idea: How about a large ferrite rod on the end of a
walking staff, on top of a backpack, or hidden inside a top-hat?

[ https://sites.google.com/site/g3xbmqrp3/antennas/ferrite_tx ]

On 1/22/19 12:57 PM, Wayne Burdick wrote:
> 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: [KX3] Urban stealth HF: Inside-the-backpack loop antenna?

RichA
In reply to this post by Elecraft mailing list
Ref: Homless......let's not forget the ever present shopping cart! Get a BIG one. It can be used as a counter poise in place of a set of radials or a drag wire. One could also try loading the shopping cart and using it as an antenna since the wheels are composed of a non-conductive set of wheels so the cart would be above ground.

Just sayin'

Vy 73 es gud DX!

Rich Arland   K7SZ   WPE7BYR
Radio/electronics archaeologist
Author: The ARRL's Low Power Communicatoions
Bent Dipole Ranch, Dacula, GA
http://commobunker.blogspot.com/



________________________________
From: [hidden email] <[hidden email]> on behalf of Michael Blake via Elecraft <[hidden email]>
Sent: Tuesday, January 22, 2019 4:40 PM
To: Mark Goldberg
Cc: Elecraft Reflector; KX3
Subject: Re: [Elecraft] [KX3] Urban stealth HF: Inside-the-backpack loop antenna?

Mark (W7MLG),  It is scary how perfectly sane and normal your suggestions sound to me :)

Very 73 - Mike - K9JRI







> On Jan 22, 2019, at 4:32 PM, Mark Goldberg <[hidden email]> wrote:
>
> I would expect any high Q antenna like a loop would be detuned by any
> movement or any metal you pass by. One more reason to support automatic
> mobile screwdriver / mag loop antenna tuning on the KX series.
> A flag on a backpack would be more or less ignored. Just put a flag on the
> top of the AX1. Counterpoise is an issue though. Maybe a short one down
> your leg?
>
> Now, if you dressed as a homeless or otherwise distressed person, lots of
> weird things are possible, tinfoil hat with a big flag, dragged wire
> disguised as one of those fake animals on a leash, etc. The weirder, the
> more people will ignore you.
>
> Hopefully taken in the spirit of which it is posted.
>
> 73,
>
> Mark
> W7MLG
>
>
> On Tue, Jan 22, 2019 at 1:57 PM Wayne Burdick [hidden email] [KX3] <
> [hidden email]> wrote:
>

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

kevinr@coho.net
In reply to this post by wayne burdick
There may be other options.  A serpentine pattern fed at the center
could give you enough length for a 10 m or larger dipole. I've seen
serpentine F antennas on printed circuit boards.  I've also seen spiral
patterns used so I know they work to some extent.

If a dipole cut for 14 MHz is ~ 400 inches long it would take 11 up and
down segments of 36" each to stuff it inside your pack. I'm sure the
serpentine factor will change the length needed but with a bit of
tweaking this could work.

Or feed it at one end for a 40 meter monopole (a counterpoise could be
woven into the pack).

    73 & GL,

        Kevin.  KD5ONS

-


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

Michael Chowning
In reply to this post by wayne burdick
Just for grins, look into this link, from Ohio State University from back in 2011!
https://news.osu.edu/antennas-in-your-clothes--new-design-could-pave-the-way/ <https://news.osu.edu/antennas-in-your-clothes--new-design-could-pave-the-way/>
There are also articles more recently (2018) on electronics in one’s clothes, and computers in one’s clothes in this website’s news as well.
    Mike, N8TTR

> On Jan 22, 2019, at 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: Urban stealth HF: Inside-the-backpack loop antenna?

Bill K9YEQ
In reply to this post by wayne burdick
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



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

wayne burdick
Administrator
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
> 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: Urban stealth HF: Inside-the-backpack loop antenna?

David Gilbert
In reply to this post by kevinr@coho.net


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?

wayne burdick
Administrator
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
>
> ______________________________________________________________
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Re: Urban stealth HF: Inside-the-backpack loop antenna?

Martin Sole-3
Hook it up to your KPA1500 and you've got whole house illumination!

Martin, HS0ZED



On 23/01/2019 13:11, Wayne Burdick wrote:

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

W2xj
In reply to this post by wayne burdick
The problem I see is Uncontrolled contents of backpack detuning the loop.

Sent from my iPad

> On Jan 22, 2019, at 10:56 PM, Wayne Burdick [hidden email] [KX3] <[hidden email]> 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
>> 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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