Flex dryer vent hose loop antenna

[Jeff Liebermann]

I've been thinking of building a rather different magnetic loop
antenna. Instead of the usual rigid loop and adjustable tuning
capacitor, I want to try a flexible loop and a fixed capacitor. The
idea is to eliminate the cost of the tunable vacuum capacitor or
cheese grater butterfly capacitor.

For a loop, I propose to use a flexible aluminum dryer vent hose:
<https://www.google.com/search?tbm=isch&q=flexible+dryer+vent+duct>
<http://www.ipagepro.com/dryerventsolutionsllc/logos/BTD48.png>
<http://ace.imageg.net/graphics/product_images/pACE3-17458764enh-z8.jpg>
I've used similar hoses in my giant inflatable rubber ducky antenna
experiments. The major point of failure was that the spiral steel
wire antenna inside the hose produced some hot spots, which melted a
hole in the vinyl jacket. However, with an aluminum jacket, all the
RF will be on the outside, and there's no vinyl to melt.

The 8ft dryer hose will (somehow) form a loop when inflated with air
from a bicycle or hand pump. Inside the dryer hose is a length of
small diameter bungee cord to help collapse the loop. When hose is
inflated, the loop expands, which also tunes the loop to the desired
frequency.

One nice feature is that with the loop deflated and collapsed, it's
sufficiently small for portable or stealth use. Fully inflated, an
8ft hose should produce a 31" diameter loop.

The rest is fairly conventional. A small wire loop inside the loop to
provide impedance matching and coupling for the 50 ohm feed. Maybe
some kind of tuning indicator (small fluorescent tube). I'm undecided
on whether to mount it vertically, which requires a prop, or
horizontally, which can be done on an insulated table surface.

Permission to steal and use this idea is hereby granted, as long as
you fail to mention my identity in the event that your sanity is
questioned by the neighbors or local authorities. No patents are
pending.




--
Jeff Liebermann je...@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

[rickman]

When you say dryer hose, you mean the corrugated aluminum tube that is 3
or 4 inches in diameter. That might work for a loop antenna, but I
think the corrugations are hard to collapse once you expand them. So I
doubt it will work as the tuning element unless you simply change the
shape of the loop rather than keeping it a circle with an adjustable size.

I used some of this stuff in a larger diameter to connect a humidifier
and it was flexible enough to extend and shape, but didn't go back
hardly at all.

--

Rick

[Paul Drahn]

Probable should clear the lint out first!

Paul, KD7HB

[Jeff Liebermann]

On Sun, 1 Nov 2015 18:31:55 -0500, rickman <gnu...@gmail.com> wrote:

>When you say dryer hose, you mean the corrugated aluminum tube that is 3
>or 4 inches in diameter.

Yep. Just like the stuff in the links provided.

>That might work for a loop antenna, but I
>think the corrugations are hard to collapse once you expand them. So I
>doubt it will work as the tuning element unless you simply change the
>shape of the loop rather than keeping it a circle with an adjustable size.

The bungee cord down the middle is suppose to help collapse the hose.
I must confess that I haven't tried it. If that doesn't work, then
some elastic cords. If that fails, a nylon rope and some external
springs.

>I used some of this stuff in a larger diameter to connect a humidifier
>and it was flexible enough to extend and shape, but didn't go back
>hardly at all.

Yep. It won't go back by itself and needs some additional help.
Anyway, if you want to get your picture in QST as the building of the
worlds strangest and probably cheapest loop antenna, here's your
chance.

[Jeff Liebermann]

On Sun, 1 Nov 2015 18:10:56 -0800, Paul Drahn
<pdr...@webformixair.com> wrote:

>Probable should clear the lint out first!
>Paul, KD7HB

I know that hams are cheap, but I didn't realize that extended to
stealing the neighbors dryer vent hose in order to build an antenna. I
highly recommend purchasing a new hose, which comes pre-cleaned:
<http://www.acehardware.com/family/index.jsp?categoryId=2627981>

Incidentally, there's no requirement that the entire loop be made from
expandable hose. The loop could be in the form of a square loop,
where the flat base and flat top are rigid aluminum structures, and
the two vertical sections are flexible dryer vent hose. The weight of
the flat top would help collapse the antenna although I suspect that
springs or weights would work better.

It's not like inflatable antennas and structures are a new thing:
<http://ltaprojects.com/towers/inflatable-antenna-video-towers/ham>

[rickman]

On 11/1/2015 9:27 PM, Jeff Liebermann wrote:
> On Sun, 1 Nov 2015 18:31:55 -0500, rickman <gnu...@gmail.com> wrote:
>
>> When you say dryer hose, you mean the corrugated aluminum tube that is 3
>> or 4 inches in diameter.
>
> Yep. Just like the stuff in the links provided.
>
>> That might work for a loop antenna, but I
>> think the corrugations are hard to collapse once you expand them. So I
>> doubt it will work as the tuning element unless you simply change the
>> shape of the loop rather than keeping it a circle with an adjustable size.
>
> The bungee cord down the middle is suppose to help collapse the hose.
> I must confess that I haven't tried it. If that doesn't work, then
> some elastic cords. If that fails, a nylon rope and some external
> springs.
>
>> I used some of this stuff in a larger diameter to connect a humidifier
>> and it was flexible enough to extend and shape, but didn't go back
>> hardly at all.
>
> Yep. It won't go back by itself and needs some additional help.
> Anyway, if you want to get your picture in QST as the building of the
> worlds strangest and probably cheapest loop antenna, here's your
> chance.

Ok, so if you can force it to shrink with springs or ropes or whatever,
then something will be needed to force it to expand again. I'm having
trouble seeing how this will work without the antenna losing all shape.
These tubes are just not really easy to manipulate. They are intended
to be bent once with more than a little force but more importantly very
controlled force.

I'm not sure the inductance will change all that much. I have never
seen a calculation for the inductance of an accordion. It may have a
rather limited tuning range compared to a typical variable cap. At
least the frequency will scale the right way with size. Smaller loop,
lower inductance, higher frequency which will keep the radiation
resistance high.

--

Rick

[Jeff Liebermann]

On Sun, 1 Nov 2015 21:58:32 -0500, rickman <gnu...@gmail.com> wrote:

>Ok, so if you can force it to shrink with springs or ropes or whatever,
>then something will be needed to force it to expand again.

Yep. A bicycle pump, hand pump, crank pump, bellows pump, electric
pump, or pressure vessel will all inflate the antenna.

>I'm having
>trouble seeing how this will work without the antenna losing all shape.

Below some pressure level, it will probably flop over if mounted
vertically. That's why I mumbled that I wasn't sure if it should be
mounted vertically with a support pole, or horizontally on a flat
sheet of plywood. Both will work, but I'm not sure which is better.

>These tubes are just not really easy to manipulate. They are intended
>to be bent once with more than a little force but more importantly very
>controlled force.

In other words, after a few inflation deflation cycles, it might fall
apart. I have a few that I bought for the inflatable antenna project.
It looked quite flexible to me but I'll test it to be sure.

>I'm not sure the inductance will change all that much. I have never
>seen a calculation for the inductance of an accordion. It may have a
>rather limited tuning range compared to a typical variable cap. At
>least the frequency will scale the right way with size. Smaller loop,
>lower inductance, higher frequency which will keep the radiation
>resistance high.

Good point. At one time, I was wondering how to increase the
bandwidth of a yagi antenna. I knew that rounding the ends of the
elements would increase the bandwidth because there was no single
length for which to consider the "end" of the antenna rod. Similarly,
when calculating the rod length of a yagi antenna, the RF path around
the center boom must be added to the rod length. That made me wonder
if I could roughen the antenna rod to produce the same effect. I
guess corrugation might be considered the ultimate form of antenna
"roughness". The question was would the antenna length be the
distance from end to end of the accordion, or would it be the distance
traveled across the surface along all the ups and downs of the
accordion.

What I found was that the effect varies with frequency and of course
the accordion geometry. At <1MHz, the resonant length was the surface
distance traveled. In other words, expanding the accordion had little
effect on the antenna resonance. At much higher frequencies (about
150 MHz), there was enough capacitance between the accordion "sides"
that the antenna was effectively shortened and the resonant frequency
was the end to end distance. However, that's not exactly true because
there were multiple path lengths which could be considered resonant,
much like the rounded end on the rod. So, at low frequencies, my
scheme probably won't work. At higher frequencies, maybe. Your task,
should you decide to accept it, is to try it. All it will take is a
length of flex aluminum dryer hose and an LRC meter.

Please note that my testing was not a proper lab test but more like
screwing around with a grid dipper, LRC meter, and network analyzer to
help settle a lunch time argument.

[rickman]

On 11/1/2015 11:32 PM, Jeff Liebermann wrote:
> On Sun, 1 Nov 2015 21:58:32 -0500, rickman <gnu...@gmail.com> wrote:
>
>> Ok, so if you can force it to shrink with springs or ropes or whatever,
>> then something will be needed to force it to expand again.
>
> Yep. A bicycle pump, hand pump, crank pump, bellows pump, electric
> pump, or pressure vessel will all inflate the antenna.

Ok, that might be workable. I think the tube will need a liner. I'm
not sure this stuff will be easy to seal.

>> I'm having
>> trouble seeing how this will work without the antenna losing all shape.
>
> Below some pressure level, it will probably flop over if mounted
> vertically. That's why I mumbled that I wasn't sure if it should be
> mounted vertically with a support pole, or horizontally on a flat
> sheet of plywood. Both will work, but I'm not sure which is better.

You are assuming it will maintain something remotely like a circle. I
don't see that happening. Have you worked with this stuff? Maybe what
you have is more pliable than the stuff I used.

>> These tubes are just not really easy to manipulate. They are intended
>> to be bent once with more than a little force but more importantly very
>> controlled force.
>
> In other words, after a few inflation deflation cycles, it might fall
> apart. I have a few that I bought for the inflatable antenna project.
> It looked quite flexible to me but I'll test it to be sure.

I don't mean fall apart necessarily, but just not be much like a loop
antenna. I think the hard part will be shrinking it back down and
keeping its shape. Proof of the pudding...

>> I'm not sure the inductance will change all that much. I have never
>> seen a calculation for the inductance of an accordion. It may have a
>> rather limited tuning range compared to a typical variable cap. At
>> least the frequency will scale the right way with size. Smaller loop,
>> lower inductance, higher frequency which will keep the radiation
>> resistance high.
>
> Good point. At one time, I was wondering how to increase the
> bandwidth of a yagi antenna. I knew that rounding the ends of the
> elements would increase the bandwidth because there was no single
> length for which to consider the "end" of the antenna rod. Similarly,
> when calculating the rod length of a yagi antenna, the RF path around
> the center boom must be added to the rod length. That made me wonder
> if I could roughen the antenna rod to produce the same effect. I
> guess corrugation might be considered the ultimate form of antenna
> "roughness". The question was would the antenna length be the
> distance from end to end of the accordion, or would it be the distance
> traveled across the surface along all the ups and downs of the
> accordion.

There are helically wound antennas that have a similar issue. I have
yet to see any equations to model them. I wonder if they work or not,
in the sense of any better than a simple loop.

> What I found was that the effect varies with frequency and of course
> the accordion geometry. At <1MHz, the resonant length was the surface
> distance traveled. In other words, expanding the accordion had little
> effect on the antenna resonance. At much higher frequencies (about
> 150 MHz), there was enough capacitance between the accordion "sides"
> that the antenna was effectively shortened and the resonant frequency
> was the end to end distance. However, that's not exactly true because
> there were multiple path lengths which could be considered resonant,
> much like the rounded end on the rod. So, at low frequencies, my
> scheme probably won't work. At higher frequencies, maybe. Your task,
> should you decide to accept it, is to try it. All it will take is a
> length of flex aluminum dryer hose and an LRC meter.

I don't have any equipment to date. I have a couple of projects ahead
of this if I decide to build something.

> Please note that my testing was not a proper lab test but more like
> screwing around with a grid dipper, LRC meter, and network analyzer to
> help settle a lunch time argument.

You clearly have much more experience than I do. I wold barely know how
to use a SWR meter and don't have an LRC meter... I can't remember what
a grid dip meter is. :(

--

Rick

[amdx]

On 11/1/2015 10:32 PM, Jeff Liebermann wrote:
> On Sun, 1 Nov 2015 21:58:32 -0500, rickman <gnu...@gmail.com> wrote:
>
>> Ok, so if you can force it to shrink with springs or ropes or whatever,
>> then something will be needed to force it to expand again.
>
> Yep. A bicycle pump, hand pump, crank pump, bellows pump, electric
> pump, or pressure vessel will all inflate the antenna.
>
>> I'm having
>> trouble seeing how this will work without the antenna losing all shape.
>
> Below some pressure level, it will probably flop over if mounted
> vertically. That's why I mumbled that I wasn't sure if it should be
> mounted vertically with a support pole, or horizontally on a flat
> sheet of plywood. Both will work, but I'm not sure which is better.

Hang it upside down.

Mikek

[Jeff Liebermann]

On Mon, 2 Nov 2015 00:28:03 -0500, rickman <gnu...@gmail.com> wrote:

>You are assuming it will maintain something remotely like a circle. I
>don't see that happening. Have you worked with this stuff? Maybe what
>you have is more pliable than the stuff I used.

I've worked with the vinyl dryer hose, but not the aluminum foil
variety. With the vinyl, I was using the helical "Slinky" part of the
hose as an HF antenna. As I mentioned, the steel spring got hot and
melted the vinyl. The actual inflatable antenna was a vertical
monopole, so I never even tried to make a loop, and am not sure it
will work. That's why I'm trying to recruit someone else to do the
dirty work. I guess I could go shopping and do it myself, but I'm
kinda busy this week (mostly recovering from the last 3 week of
overwork). I suspect that there might be problems if I use too much
air pressure. With the monopole, the hose would handle about 30 psi
before producing a leak. It thinks that's more than enough to inflate
the loop, but might not be enough to be self supporting, especially
with a capacitor at the top.

>I don't mean fall apart necessarily, but just not be much like a loop
>antenna. I think the hard part will be shrinking it back down and
>keeping its shape. Proof of the pudding...

The optimum shape is a circle with square, hexagon and octagon shapes
being a tolerable facsimile. I guess the question is whether a random
pretzel shape will work. Dunno, difficult to simulate, but easy to
try.

>There are helically wound antennas that have a similar issue. I have
>yet to see any equations to model them. I wonder if they work or not,
>in the sense of any better than a simple loop.

One of the local club members build a 160 meter vertical rubber ducky
(helical antenna) with ground radials and ended up with a usable
bandwidth of about 2KHz. Keeping it tuned on frequency was a
challenge. I think it was only about 10ft high and reportedly worked
fairly well. I tried to model it with 4NEC2 but gave up for some
forgotten reason. I think it was my inability to model the ground
characteristics. Based on this example, I would say a loop would be
better because the grounding isn't part of the puzzle.

>I don't have any equipment to date. I have a couple of projects ahead
>of this if I decide to build something.

No test equipment? It's difficult to build anything without some
basic RF equipment. I can provide a basic shopping list if you would
like. My shop, which I've been told should be repurposed a museum.
<http://802.11junk.com/jeffl/pics/home/slides/lab.html>

>You clearly have much more experience than I do. I wold barely know how
>to use a SWR meter and don't have an LRC meter... I can't remember what
>a grid dip meter is. :(

Sigh. I have 4 assorted grid dip meters. I can mail you one if you
would like to play. It's very handy for measuring the resonant
frequencies of any LC circuit or antenna. It's not very accurate but
will get you in the ballpark or at least tell you if you're too high
or too low in frequency. Like this, but with more paint chipped off
and the case missing. At least all the coils are there.
<http://www.universal-radio.com/used/W483lrg.jpg>
Note that it won't go down to 60 KHz although I tried making a coil
that covered the range.

Argh... I'm late (again).

[Jeff Liebermann]

On Mon, 2 Nov 2015 09:13:38 -0600, amdx <noj...@knology.net> wrote:

>> Below some pressure level, it will probably flop over if mounted
>> vertically. That's why I mumbled that I wasn't sure if it should be
>> mounted vertically with a support pole, or horizontally on a flat
>> sheet of plywood. Both will work, but I'm not sure which is better.

>Hang it upside down.
> Mikek

But, all the photons will fall out of the loop that way.

Actually, there's a problem. It doesn't work as well upside down.
The magnetic loop has a rather directional field and takeoff angle and
does NOT have a constant current around the loop:
<http://www.nonstopsystems.com/radio/vids-ant/antenna-Mag-Loop-Demo1.wmv>
<https://www.youtube.com/watch?v=SUYI81dkEMA>

I suspect that an inverted loop will send most of the RF into the
ground. I should probably test this.
<http://www.nonstopsystems.com/radio/img-ant/antenna-magloop-rad-angle.gif>

You might find this interesting on designing the 50 ohm matching
network to the loop, where the impedance varies by where it's fed:
<http://www.g0cwt.co.uk/magloops/new_page_6.htm>

[Jeff Liebermann]

On Mon, 02 Nov 2015 16:39:09 -0800, Jeff Liebermann <je...@cruzio.com>
wrote:

>You might find this interesting on designing the 50 ohm matching
>network to the loop, where the impedance varies by where it's fed:
><http://www.g0cwt.co.uk/magloops/new_page_6.htm>

More:
<https://www.youtube.com/watch?v=NdofH6R22Dg>
Skip forward to 12:03 for an interesting comment:
"Commercial loops are usually radiating towards the ground and
a lot of the signal is warming the snails. I don't know how
so many people could have got it so wrong for so long".

[Paul Drahn]

On 11/1/2015 6:42 PM, Jeff Liebermann wrote:
> On Sun, 1 Nov 2015 18:10:56 -0800, Paul Drahn
> <pdr...@webformixair.com> wrote:
>
>> Probable should clear the lint out first!
>> Paul, KD7HB
>
> I know that hams are cheap, but I didn't realize that extended to
> stealing the neighbors dryer vent hose in order to build an antenna. I
> highly recommend purchasing a new hose, which comes pre-cleaned:
> <http://www.acehardware.com/family/index.jsp?categoryId=2627981>
>
> Incidentally, there's no requirement that the entire loop be made from
> expandable hose. The loop could be in the form of a square loop,
> where the flat base and flat top are rigid aluminum structures, and
> the two vertical sections are flexible dryer vent hose. The weight of
> the flat top would help collapse the antenna although I suspect that
> springs or weights would work better.
>
> It's not like inflatable antennas and structures are a new thing:
> <http://ltaprojects.com/towers/inflatable-antenna-video-towers/ham>
>

I am looking at the vent pipe from our reflow oven. We made it up from
4", 4' long vent pipe pieces, including "T" and "EL" pieces. That should
work better than the expandable dryer vent hose.

Paul, KD7HB

[rickman]

I think the point is that the flex tubing antenna can be tuned by
adjusting the loop rather than the capacitor. Interesting idea although
it may not prove practical in the end.

--

Rick

[rickman]

On 11/2/2015 2:49 PM, Jeff Liebermann wrote:
> On Mon, 2 Nov 2015 00:28:03 -0500, rickman <gnu...@gmail.com> wrote:
>
>> You are assuming it will maintain something remotely like a circle. I
>> don't see that happening. Have you worked with this stuff? Maybe what
>> you have is more pliable than the stuff I used.
>
> I've worked with the vinyl dryer hose, but not the aluminum foil
> variety. With the vinyl, I was using the helical "Slinky" part of the
> hose as an HF antenna. As I mentioned, the steel spring got hot and
> melted the vinyl.

Sure, there is nothing good about the slinky dryer tube you mention.
Steel has horrible conductivity with its high resistance *and* very
shallow skin effect. But even a copper wire of that small gauge would
not be effective in a transmitter loop antenna.

> The actual inflatable antenna was a vertical
> monopole, so I never even tried to make a loop, and am not sure it
> will work. That's why I'm trying to recruit someone else to do the
> dirty work. I guess I could go shopping and do it myself, but I'm
> kinda busy this week (mostly recovering from the last 3 week of
> overwork). I suspect that there might be problems if I use too much
> air pressure. With the monopole, the hose would handle about 30 psi
> before producing a leak. It thinks that's more than enough to inflate
> the loop, but might not be enough to be self supporting, especially
> with a capacitor at the top.

I bought a piece of dryer aluminum to use in another experiment (btw, a
four foot column does not create much chimney effect over a 100 W light
bulb) and they are stiff, too stiff to be worked by a balloon. Also
they bend by expanding one side and not the other. Once it is bent it
is a bit hard to straighten out. I am not trying to dampen your
spirits. I suggest you buy a short piece of this stuff and just bend it
by hand. Get a feel for it and see if you think this type of tube can
be manipulated by simple machinery. I think it will cost less than $10
to try this.

>> I don't mean fall apart necessarily, but just not be much like a loop
>> antenna. I think the hard part will be shrinking it back down and
>> keeping its shape. Proof of the pudding...
>
> The optimum shape is a circle with square, hexagon and octagon shapes
> being a tolerable facsimile. I guess the question is whether a random
> pretzel shape will work. Dunno, difficult to simulate, but easy to
> try.

The prevailing wisdom is the area is what matters. Given what I saw in
those videos which seem to show directionality in the plane of the loop,
I'm not so sure. That and the results people seem to get with helical
loop antennas make me think we don't really "get" loop antennas.

Thanks for the offer. Let me get my other stuff out of the way and
maybe I'll take you up on this.

--

Rick

[amdx]

On 11/2/2015 6:39 PM, Jeff Liebermann wrote:
> On Mon, 2 Nov 2015 09:13:38 -0600, amdx <noj...@knology.net> wrote:
>
>>> Below some pressure level, it will probably flop over if mounted
>>> vertically. That's why I mumbled that I wasn't sure if it should be
>>> mounted vertically with a support pole, or horizontally on a flat
>>> sheet of plywood. Both will work, but I'm not sure which is better.
>
>> Hang it upside down.
>> Mikek
>
> But, all the photons will fall out of the loop that way.
>
> Actually, there's a problem. It doesn't work as well upside down.
> The magnetic loop has a rather directional field and takeoff angle and
> does NOT have a constant current around the loop:
> <http://www.nonstopsystems.com/radio/vids-ant/antenna-Mag-Loop-Demo1.wmv>
> <https://www.youtube.com/watch?v=SUYI81dkEMA>
>
> I suspect that an inverted loop will send most of the RF into the
> ground. I should probably test this.
> <http://www.nonstopsystems.com/radio/img-ant/antenna-magloop-rad-angle.gif>
>
> You might find this interesting on designing the 50 ohm matching
> network to the loop, where the impedance varies by where it's fed:
> <http://www.g0cwt.co.uk/magloops/new_page_6.htm>
>

Sorry Jeff, When my post didn't show up, I noticed I sent it to you.
Here it is for the rest.



Just to add to the confusion,
Helically Loaded


You might glean info from here, or at the least

admire all the work put into the projects.



> http://theradioboard.com/rb/viewtopic.php?f=10&t=4399

Copper doughnut with lots of solder connections
> http://www.aa5tb.com/jl1boh_03.jpg

http://www.hlmagneticloopantennas.com/

Hmm, I read a few comments, maybe not the way to go.



Mikek

[rickman]

On 11/2/2015 7:39 PM, Jeff Liebermann wrote:
> On Mon, 2 Nov 2015 09:13:38 -0600, amdx <noj...@knology.net> wrote:
>
>>> Below some pressure level, it will probably flop over if mounted
>>> vertically. That's why I mumbled that I wasn't sure if it should be
>>> mounted vertically with a support pole, or horizontally on a flat
>>> sheet of plywood. Both will work, but I'm not sure which is better.
>
>> Hang it upside down.
>> Mikek
>
> But, all the photons will fall out of the loop that way.
>
> Actually, there's a problem. It doesn't work as well upside down.
> The magnetic loop has a rather directional field and takeoff angle and
> does NOT have a constant current around the loop:
> <http://www.nonstopsystems.com/radio/vids-ant/antenna-Mag-Loop-Demo1.wmv>

I don't get this video. I can't really hear what he is saying so when
he says at the end, "this is not what you would expect" I don't get it.


> <https://www.youtube.com/watch?v=SUYI81dkEMA>

This video is about the voltage and current around a loop, but he says
it is a <1/10 wave loop, but I can't tell that. He has another video
showing the directionality of a 1/4 wave delta antenna. I'm wondering
if this is also a 1/4 wave antenna.

> I suspect that an inverted loop will send most of the RF into the
> ground. I should probably test this.
> <http://www.nonstopsystems.com/radio/img-ant/antenna-magloop-rad-angle.gif>

Which type of loop antenna are you talking about, 1/4 wave, or <1/10
wave (small, magnetic)? I can't tell anything about this antenna and it
seems to contradict the other video.

> You might find this interesting on designing the 50 ohm matching
> network to the loop, where the impedance varies by where it's fed:
> <http://www.g0cwt.co.uk/magloops/new_page_6.htm>

--

Rick

[Ian Jackson]

In message <n1c48i$o5e$1...@dont-email.me>, rickman <gnu...@gmail.com>
writes


>
>> <https://www.youtube.com/watch?v=SUYI81dkEMA>

When he's measuring towards the capacitor, won't the presence of his
hand be causing the loop to de-tune - hence less current?
>

--
Ian

[John S]

Yes. But, is it measurable?

[Ian Jackson]

In message <n1cuth$p33$4...@dont-email.me>, John S <Sop...@invalid.org>
writes

Being a high-Q circuit, I would think that a small amount of additional
C would cause considerable de-tuning.
--
Ian

[rickman]

Wouldn't that also give less voltage? That didn't seem to go down any.

--

Rick

[Ian Jackson]

In message <n1d8s4$jdi$1...@dont-email.me>, rickman <gnu...@gmail.com>
writes

While I'm not really looking for flaws in the experiment, I've had
another quick look, and I don't see anywhere where the voltage is being
measured. I would have expected at least the input drive (voltage,
current or power) to be monitored just to check that it didn't fluctuate
(too much).

I note that the analyser VSWR meter reading increases as the current
probe is moved towards the capacitor - but what is it measuring? Is it
measuring the SWR where the probe is - and if so, how? Is there any
reference ground connection (which I'm pretty sure an SWR meter needs)?
--
Ian

[Jeff Liebermann]

On Wed, 4 Nov 2015 00:17:11 -0500, rickman <gnu...@gmail.com> wrote:

>On 11/2/2015 7:39 PM, Jeff Liebermann wrote:
>> On Mon, 2 Nov 2015 09:13:38 -0600, amdx <noj...@knology.net> wrote:
>>
>>>> Below some pressure level, it will probably flop over if mounted
>>>> vertically. That's why I mumbled that I wasn't sure if it should be
>>>> mounted vertically with a support pole, or horizontally on a flat
>>>> sheet of plywood. Both will work, but I'm not sure which is better.
>>
>>> Hang it upside down.
>>> Mikek
>>
>> But, all the photons will fall out of the loop that way.
>>
>> Actually, there's a problem. It doesn't work as well upside down.
>> The magnetic loop has a rather directional field and takeoff angle and
>> does NOT have a constant current around the loop:
>> <http://www.nonstopsystems.com/radio/vids-ant/antenna-Mag-Loop-Demo1.wmv>
>
>I don't get this video. I can't really hear what he is saying so when
>he says at the end, "this is not what you would expect" I don't get it.

I had the same problem. I would guess(tm) that what he's mumbling is
that one would expect the current to be constant around all parts of
the loop, yet it displays obvious maxima and minima.

>> <https://www.youtube.com/watch?v=SUYI81dkEMA>
>
>This video is about the voltage and current around a loop, but he says
>it is a <1/10 wave loop, but I can't tell that. He has another video
>showing the directionality of a 1/4 wave delta antenna. I'm wondering
>if this is also a 1/4 wave antenna.

At 6:30 in the above video, he proclaims that it's a 1/4 wave loop.
At 6:42, the MFJ-259B shows 29.555 MHz on the display. I couldn't
find where he said it was a <1/10 wave loop. <1/10 wave is the
defacto definition of a "small" loop.

>> I suspect that an inverted loop will send most of the RF into the
>> ground. I should probably test this.
>> <http://www.nonstopsystems.com/radio/img-ant/antenna-magloop-rad-angle.gif>
>
>Which type of loop antenna are you talking about, 1/4 wave, or <1/10
>wave (small, magnetic)? I can't tell anything about this antenna and it
>seems to contradict the other video.

I'm not saying anything about the drawing except that it shows that
the loop might be somewhat directional, which might be a problem.
Where's the contradiction?
<http://www.nonstopsystems.com/radio/frank_radio_antenna_magloop.htm>

Gone...(again).

[rickman]

On 11/5/2015 8:40 PM, Jeff Liebermann wrote:
> On Wed, 4 Nov 2015 00:17:11 -0500, rickman <gnu...@gmail.com> wrote:
>
>> On 11/2/2015 7:39 PM, Jeff Liebermann wrote:
>>> On Mon, 2 Nov 2015 09:13:38 -0600, amdx <noj...@knology.net> wrote:
>>>
>>>>> Below some pressure level, it will probably flop over if mounted
>>>>> vertically. That's why I mumbled that I wasn't sure if it should be
>>>>> mounted vertically with a support pole, or horizontally on a flat
>>>>> sheet of plywood. Both will work, but I'm not sure which is better.
>>>
>>>> Hang it upside down.
>>>> Mikek
>>>
>>> But, all the photons will fall out of the loop that way.
>>>
>>> Actually, there's a problem. It doesn't work as well upside down.
>>> The magnetic loop has a rather directional field and takeoff angle and
>>> does NOT have a constant current around the loop:
>>> <http://www.nonstopsystems.com/radio/vids-ant/antenna-Mag-Loop-Demo1.wmv>
>>
>> I don't get this video. I can't really hear what he is saying so when
>> he says at the end, "this is not what you would expect" I don't get it.
>
> I had the same problem. I would guess(tm) that what he's mumbling is
> that one would expect the current to be constant around all parts of
> the loop, yet it displays obvious maxima and minima.

He isn't saying anything about the current since he isn't measuring
current. I think the "isn't what you would expect" maybe be about
polarization.

>>> <https://www.youtube.com/watch?v=SUYI81dkEMA>
>>
>> This video is about the voltage and current around a loop, but he says
>> it is a <1/10 wave loop, but I can't tell that. He has another video
>> showing the directionality of a 1/4 wave delta antenna. I'm wondering
>> if this is also a 1/4 wave antenna.
>
> At 6:30 in the above video, he proclaims that it's a 1/4 wave loop.
> At 6:42, the MFJ-259B shows 29.555 MHz on the display. I couldn't
> find where he said it was a <1/10 wave loop. <1/10 wave is the
> defacto definition of a "small" loop.

The start says the purpose is to settle the dispute about current
distribution in a < 1/10 wave loop. Doesn't make sense he would be
doing that with 1/4 wave antenna. At 2:45 it says this loop is < 1/10
wave on 10.5 meters 28.26 MHz.

The comment at 6:30 is about the impedance in a 1/4 wave loop, but he
isn't saying this *is* a 1/4 wave loop. I believe the 1/4 wave loop is
the one he uses in the next clip, but this is a bit confusing.

>>> I suspect that an inverted loop will send most of the RF into the
>>> ground. I should probably test this.
>>> <http://www.nonstopsystems.com/radio/img-ant/antenna-magloop-rad-angle.gif>
>>
>> Which type of loop antenna are you talking about, 1/4 wave, or <1/10
>> wave (small, magnetic)? I can't tell anything about this antenna and it
>> seems to contradict the other video.
>
> I'm not saying anything about the drawing except that it shows that
> the loop might be somewhat directional, which might be a problem.
> Where's the contradiction?
> <http://www.nonstopsystems.com/radio/frank_radio_antenna_magloop.htm>

If you take this drawing literally it shows a maximum at 30-45 degrees
from horizontal while all the others show a max at the capacitor. I
don't know that this diagram is intended to show field strength, rather
just that it may vary and the angle is what you should measure.

There will be interaction with the ground unless the antenna is spaced
well above it. Once that is done the remaining radiation pattern will
be far field which is very different from near field. So I think the
"radiating into the ground" thing may be overstated. Place the loop
horizontal and it will radiate 360° with a null at the ground. No
rotator needed.

--

Rick

[Jeff Liebermann]

You might want to grab and read this:
"The Underestimated Magnetic Loop HF Antenna V1.2"
by Leigh Turner VK5KLT
<http://802.11junk.com/jeffl/antennas/magnetic-loop/_The%20Underestimated%20Magnetic%20Loop%20HF%20Antenna_V1.%202.pdf>

You may have read a previous version. The author updated it recently
and posted it to the Yahoo Magloop forum in the files section:
<https://groups.yahoo.com/neo/groups/MagLoop/info>
I couldn't find it posted anywhere else on the interknot, so I took
the liberty of posting it to my web pile without permission.

I just skimmed it quickly but offhand, it looks like a very good
explanation of how a magnetic loop antenna works, without going
excessively into technobabble and equations.

[Jeff Liebermann]

You were asking about using a better dielectric than air. I found
this article:
<http://www.qrpbuilder.com/downloads/loop%20antenna%20110310.pdf>
which includes construction details for a piston capacitor arrangement
using various dielectrics. On Pg 8 is a chart of various plastics,
with dielectric constant, dielectric strength, and dissipation factor.
For cheap, the author recommends UHMW (polypropylene), which is one
tenth the cost of PTFE (Teflon).

[rickman]

On 11/8/2015 3:44 PM, Jeff Liebermann wrote:
> You might want to grab and read this:
> "The Underestimated Magnetic Loop HF Antenna V1.2"
> by Leigh Turner VK5KLT
> <http://802.11junk.com/jeffl/antennas/magnetic-loop/_The%20Underestimated%20Magnetic%20Loop%20HF%20Antenna_V1.%202.pdf>
>
> You may have read a previous version. The author updated it recently
> and posted it to the Yahoo Magloop forum in the files section:
> <https://groups.yahoo.com/neo/groups/MagLoop/info>
> I couldn't find it posted anywhere else on the interknot, so I took
> the liberty of posting it to my web pile without permission.
>
> I just skimmed it quickly but offhand, it looks like a very good
> explanation of how a magnetic loop antenna works, without going
> excessively into technobabble and equations.

Thanks. I signed up for that group, but only by email. To join Yahoo
these days you have to give a mobile number and I'm not willing to do
that. I've been getting the emails talking about this file (mostly
people saying they can't download it) but no one has made it available
outside of that group... until now.

--

Rick

[rickman]

On 11/8/2015 5:14 PM, Jeff Liebermann wrote:
> You were asking about using a better dielectric than air. I found
> this article:
> <http://www.qrpbuilder.com/downloads/loop%20antenna%20110310.pdf>
> which includes construction details for a piston capacitor arrangement
> using various dielectrics. On Pg 8 is a chart of various plastics,
> with dielectric constant, dielectric strength, and dissipation factor.
> For cheap, the author recommends UHMW (polypropylene), which is one
> tenth the cost of PTFE (Teflon).

Yeah, but he doesn't address the issue of temperature dependance of Er.
I don't even see it in his table.

The text says he used PEX (cross linked polyethylene) for the capacitor,
but I can't find much info on the electrical characteristics. The one
that is hardest to find is the temperature dependence of Er. I don't
see PEX in his table at all. Very odd.

The info on PEX that I can find on the web indicates it may have
problems with use outdoors, but maybe this antenna isn't intended to be
used outdoors.

--

Rick

[Jeff Liebermann]

On Sun, 8 Nov 2015 18:02:19 -0500, rickman <gnu...@gmail.com> wrote:

>On 11/8/2015 3:44 PM, Jeff Liebermann wrote:
>> You might want to grab and read this:
>> "The Underestimated Magnetic Loop HF Antenna V1.2"
>> by Leigh Turner VK5KLT
>> <http://802.11junk.com/jeffl/antennas/magnetic-loop/_The%20Underestimated%20Magnetic%20Loop%20HF%20Antenna_V1.%202.pdf>
>>
>> You may have read a previous version. The author updated it recently
>> and posted it to the Yahoo Magloop forum in the files section:
>> <https://groups.yahoo.com/neo/groups/MagLoop/info>
>> I couldn't find it posted anywhere else on the interknot, so I took
>> the liberty of posting it to my web pile without permission.
>>
>> I just skimmed it quickly but offhand, it looks like a very good
>> explanation of how a magnetic loop antenna works, without going
>> excessively into technobabble and equations.

>Thanks. I signed up for that group, but only by email. To join Yahoo
>these days you have to give a mobile number and I'm not willing to do
>that.

I signed up long ago and have been able to bypass that requirement.
Eventually, I'm sure Yahoo, Google, Microsoft, and others will make it
mandatory. What pisses me off is that the various vendors involved
claim that it's a security feature, when it's really a bad excuse for
cell phone calling and SMS spamming. Here's a possible solution:
<http://www.burnerapp.com>
Essentially, it's a throw away phone number service. I just found the
URL, so I haven't had time to try it or decode the cryptic description
on the web page.

>I've been getting the emails talking about this file (mostly
>people saying they can't download it) but no one has made it available
>outside of that group... until now.

I'm not sure of the legality or if it's ethically correct. I would
get a bit irritated if someone posted a copy of my work, instead of a
link to the original. However, as soon as I find it publicly posted
elsewhere by the author, I'll take mine down.

Some interesting comments on the magloop article:
<http://www.brisdance.com/vk4amz/VK5KLT.html>

[Jeff Liebermann]

On Sun, 8 Nov 2015 19:12:38 -0500, rickman <gnu...@gmail.com> wrote:

>On 11/8/2015 5:14 PM, Jeff Liebermann wrote:
>> You were asking about using a better dielectric than air. I found
>> this article:
>> <http://www.qrpbuilder.com/downloads/loop%20antenna%20110310.pdf>
>> which includes construction details for a piston capacitor arrangement
>> using various dielectrics. On Pg 8 is a chart of various plastics,
>> with dielectric constant, dielectric strength, and dissipation factor.
>> For cheap, the author recommends UHMW (polypropylene), which is one
>> tenth the cost of PTFE (Teflon).
>
>Yeah, but he doesn't address the issue of temperature dependance of Er.
> I don't even see it in his table.

True, but I don't think tempco is critical or required. A practical
loop antenna, with sufficiently high Q and narrow bandwidth, will
require an automatic tuning arrangement. I managed to built one where
the operating bandwidth on 80 meters was less than the occupied
bandwidth of a SSB signal. With that critical a frequency tuning,
manual or fixed tuning isn't going to work. Once you have an
automatic tuner, compensating for thermal drift is easy.

Incidentally, one of the problems I'm fighting is that the loop tuning
is different between TX and RX because the impedance of the receiver
and transmitter are slightly different and enought to detune the loop.
That's another problem that an automagic tuner should fix.

>The text says he used PEX (cross linked polyethylene) for the capacitor,
>but I can't find much info on the electrical characteristics. The one
>that is hardest to find is the temperature dependence of Er. I don't
>see PEX in his table at all. Very odd.

I use PEX plumbing pipe for coil forms, spacers, standoffs, and
spreaders. Works well, but seems a bit expensive. This might help:
<http://www.smeter.net/daily-facts/11/fact21.php>
Er = 2.3 and 60-90 kV/mm

Here's something on building a trombone capacitor:
<http://www.eham.net/ehamforum/smf/index.php?topic=70784.0;wap2>
Er = 2.25

This looks a bit more authoritative:
<http://www.comfortprosystems.com/sites/comfortprosystems.com/files/cps_aquaheat_pex_pressdrop_tec-04.pdf>
Er = 2.3

>The info on PEX that I can find on the web indicates it may have
>problems with use outdoors, but maybe this antenna isn't intended to be
>used outdoors.

Just about everything plastic has problems with UV embrittlement. The
best fix I've found is Krylon clear acrylic spray.
<http://yarchive.net/electr/plastic_uv_resistances.html>
Hint: Search Yarchive and Google for posting by Dr Barry L. Ornitz
WA4VZQ. Lots of really good info on materials, chemicals, processes,
and antennas.

Incidentally, if you dive into the Yahoo magloop files sections, there
are some photos of the insides of the MFJ-1786 mag loop.
<http://www.mfjenterprises.com/Product.php?productid=MFJ-1786>
<https://groups.yahoo.com/neo/groups/MagLoop/files/MFJ-1786/MFJ-1786%20coupling%20loop/>
Two things worthy of notice. All the aluminum parts are brazed or
welded together and the matching(?) coil inside the box appears to be
silver plated. If MFJ's reputation for cheap construction is to be
believed, they would not silver plate anything if a cheaper
alternative would work.

[rickman]

I found a discussion of this problem which listed a website for getting
phone numbers, but it seems Yahoo won't work with this. I'm not sure
what Burner app is about, but it looks like they give you a burner phone
number which will relay texts and calls. But that just means you have
to share your phone number with *them*.

>> I've been getting the emails talking about this file (mostly
>> people saying they can't download it) but no one has made it available
>> outside of that group... until now.
>
> I'm not sure of the legality or if it's ethically correct. I would
> get a bit irritated if someone posted a copy of my work, instead of a
> link to the original. However, as soon as I find it publicly posted
> elsewhere by the author, I'll take mine down.

Technically it is copyrighted. I'm not sure if that restricts the
sharing of the file or not, I think so if he hadn't shared it openly
elsewhere. Since it is there for anyone to download, I'm not sure there
can be a problem unless he says you need to take it down.

> Some interesting comments on the magloop article:
> <http://www.brisdance.com/vk4amz/VK5KLT.html>


--

Rick

[rickman]

On 11/8/2015 10:46 PM, Jeff Liebermann wrote:
> On Sun, 8 Nov 2015 19:12:38 -0500, rickman <gnu...@gmail.com> wrote:
>
>> On 11/8/2015 5:14 PM, Jeff Liebermann wrote:
>>> You were asking about using a better dielectric than air. I found
>>> this article:
>>> <http://www.qrpbuilder.com/downloads/loop%20antenna%20110310.pdf>
>>> which includes construction details for a piston capacitor arrangement
>>> using various dielectrics. On Pg 8 is a chart of various plastics,
>>> with dielectric constant, dielectric strength, and dissipation factor.
>>> For cheap, the author recommends UHMW (polypropylene), which is one
>>> tenth the cost of PTFE (Teflon).
>>
>> Yeah, but he doesn't address the issue of temperature dependance of Er.
>> I don't even see it in his table.
>
> True, but I don't think tempco is critical or required. A practical
> loop antenna, with sufficiently high Q and narrow bandwidth, will
> require an automatic tuning arrangement. I managed to built one where
> the operating bandwidth on 80 meters was less than the occupied
> bandwidth of a SSB signal. With that critical a frequency tuning,
> manual or fixed tuning isn't going to work. Once you have an
> automatic tuner, compensating for thermal drift is easy.

I'm not familiar with automatic tuners that can tune the antenna while
in use. One of the issues someone pointed out was that the dielectric
can heat up from the energy absorbed during transmission. Is an antenna
tuner real time in this case?

I crunched some numbers and found 100's of PPM change in tuned frequency
due to ambient temperature change over the course of a year for an
antenna with an air or vacuum tuning capacitor. I can find ceramic
dielectrics that would be lower than this and even in the opposite
direction to offset the natural drift. But I can't find this info for PEX.

> Incidentally, one of the problems I'm fighting is that the loop tuning
> is different between TX and RX because the impedance of the receiver
> and transmitter are slightly different and enought to detune the loop.
> That's another problem that an automagic tuner should fix.
>
>> The text says he used PEX (cross linked polyethylene) for the capacitor,
>> but I can't find much info on the electrical characteristics. The one
>> that is hardest to find is the temperature dependence of Er. I don't
>> see PEX in his table at all. Very odd.
>
> I use PEX plumbing pipe for coil forms, spacers, standoffs, and
> spreaders. Works well, but seems a bit expensive. This might help:
> <http://www.smeter.net/daily-facts/11/fact21.php>
> Er = 2.3 and 60-90 kV/mm

I'm not terribly concerned with the actual value of Er and even the
dielectric strength. What is important to me is the temperature
coefficient of Er.

> Here's something on building a trombone capacitor:
> <http://www.eham.net/ehamforum/smf/index.php?topic=70784.0;wap2>
> Er = 2.25

Interesting, but nearly every discussion I find on loop antennas has a
lot of fluff content. Here is some from this discussion, "By the way
PEX is cross linked polyethylene and is superior to using sheet Teflon
in this instance." Unless the reason is stated for considering PEX
superior to Teflon, I haven't learned anything. I'm certainly not going
to take an anonymous person's word for it.

> This looks a bit more authoritative:
> <http://www.comfortprosystems.com/sites/comfortprosystems.com/files/cps_aquaheat_pex_pressdrop_tec-04.pdf>
> Er = 2.3
>
>> The info on PEX that I can find on the web indicates it may have
>> problems with use outdoors, but maybe this antenna isn't intended to be
>> used outdoors.
>
> Just about everything plastic has problems with UV embrittlement. The
> best fix I've found is Krylon clear acrylic spray.
> <http://yarchive.net/electr/plastic_uv_resistances.html>
> Hint: Search Yarchive and Google for posting by Dr Barry L. Ornitz
> WA4VZQ. Lots of really good info on materials, chemicals, processes,
> and antennas.

I'm talking about water impacts. Humidity and rain soak into materials.
Some by absorption, others by infiltration into micro-cracks. I saw
some materials that talked about water trees in PEX. This is not a
universal problem in all plastics.

> Incidentally, if you dive into the Yahoo magloop files sections, there
> are some photos of the insides of the MFJ-1786 mag loop.
> <http://www.mfjenterprises.com/Product.php?productid=MFJ-1786>
> <https://groups.yahoo.com/neo/groups/MagLoop/files/MFJ-1786/MFJ-1786%20coupling%20loop/>
> Two things worthy of notice. All the aluminum parts are brazed or
> welded together and the matching(?) coil inside the box appears to be
> silver plated. If MFJ's reputation for cheap construction is to be
> believed, they would not silver plate anything if a cheaper
> alternative would work.

I can't get to the MagLoop files. I don't know anything about MFJ's
reputation. There are simple facts about silver that make it only very
slightly better than copper for RF circuits. I know that you can
increase the size of the conductor by less than 5% as an alternative to
using silver plating if the electrical characteristics are the goal.
Can you explain why silver is required? The numbers don't show it.

--

Rick

[amdx]

The silver is simply optimization. If you can make your coil wire 5%
bigger, you should have already done that. Then if you want to optimized
1 + 0.05, silver plate it.
Mikek

[Jeff Liebermann]

On Mon, 9 Nov 2015 01:59:06 -0500, rickman <gnu...@gmail.com> wrote:

>I'm not familiar with automatic tuners that can tune the antenna while
>in use.

The basic benefits of having a remote controller are:
1. RF safety and you're not part of the antenna system.
2. A controller is easier to umm.... control.
3. Automatic remote tuning reacts to changes when you're not looking
at the VSWR meter.
4. White knuckle tuning is difficult. Let the servos do the work.
5. It's the only effective way to tune a loop mounted on a tall pole,
tower, or roof.

>One of the issues someone pointed out was that the dielectric
>can heat up from the energy absorbed during transmission. Is an antenna
>tuner real time in this case?

Yes in receive. Probably not in transmit. In receive, you can tune
all you want and nothing will explode or catch fire. In transmit, you
can easily tune through full power and arc over the tuning capacitor.
Auto tuning also goes through the optimum VSWR point several times
during the tuning cycle. You transmitter may not like operating into
a high VSWR load during tuning.

The solution is to tune at low tranmit power levels. Once the lowest
VSWR point is found, you can increase your power. However, that
usually prevents you from "tweaking" the tuning at full power, which
is what you need to compensate for thermal drift. It's also difficult
to tune with any modulation other than CW. I think (not sure) that
some controllers have this ability, probably with warnings and
disclaimers. I wouldn't trust it. Basically, to make it work
requires a VWSR sensor and calculator that works when there's
modulation, and a tuning capacitor that can tolerate moving while
passing high currents. Arcing and welding the bearing and bushings
might be a problem.

>I crunched some numbers and found 100's of PPM change in tuned frequency
>due to ambient temperature change over the course of a year for an
>antenna with an air or vacuum tuning capacitor. I can find ceramic
>dielectrics that would be lower than this and even in the opposite
>direction to offset the natural drift. But I can't find this info for PEX.

I looked and also didn't find anything. The problem is that you don't
find tempco data for plumbing parts that were not intended to be used
for RF components.

>I'm not terribly concerned with the actual value of Er and even the
>dielectric strength. What is important to me is the temperature
>coefficient of Er.

Again, I think you might be trying to solve a problem that has already
been solved by automatic tuning (which you need anyway). Unless you
plan to transmit endlessly, you can simply press the tune button on
the controller a few times per hour, and be done with trying to
temperature stabilize the loop.

>Interesting, but nearly every discussion I find on loop antennas has a
>lot of fluff content.

RF is magic. It's difficult to explain some things.

>Here is some from this discussion, "By the way
>PEX is cross linked polyethylene and is superior to using sheet Teflon
>in this instance." Unless the reason is stated for considering PEX
>superior to Teflon, I haven't learned anything. I'm certainly not going
>to take an anonymous person's word for it.

The world is divided between practitioners of theory and of practice.
Those who favor can explain anything, but can't build anything that
actually works. Those that favor practice tend to build strange
contraptions that they can't explain. That's also probably the main
source of what you call "fluff". Sometimes, I run into a theoretician
that knows which end of the soldering iron to grab, but they are rare.
For the record, I'm a practitioner of practice, trial-n-error, and
magic. I have difficulty explaining some things, and I think you've
seen my horrid math.

>I'm talking about water impacts. Humidity and rain soak into materials.
>Some by absorption, others by infiltration into micro-cracks. I saw
>some materials that talked about water trees in PEX. This is not a
>universal problem in all plastics.

I come from the marine radio part of the business. Water and
corrosion are key parts of the marine radio problem. Many materials
are hygroscopic and will absorb moisture. Apply some RF and the water
boils out, as in a microwave oven. Do it too fast, and the material
can crack. Of course, the tuning will change. Lots of info on
plastics selection for minimal water absorption found online. For
example:
<http://www.curbellplastics.com/technical-resources/pdf/water-absorption-plastics.pdf>
Polypropylene would be my first choice for minimal water absorption.
However, it requires UV protection, which for RF applications means
some kind of conformal coating. (Adding carbon black is a bad idea as
it causes heating problems).

>There are simple facts about silver that make it only very
>slightly better than copper for RF circuits. I know that you can
>increase the size of the conductor by less than 5% as an alternative to
>using silver plating if the electrical characteristics are the goal.
>Can you explain why silver is required? The numbers don't show it.

Antennas are mounted outdoors where exposed copper is an invitation to
corrosion. If one must protect the copper with something, why not use
silver, which also improves its RF characteristics?

My magloop nightmare come true:
<http://www.mixw.co.uk/MagLoop/magloopF.htm>

[rickman]

Why can't you make the wire 5% bigger again? Where exactly is the cost?

--

Rick

[rickman]

On 11/9/2015 7:52 PM, Jeff Liebermann wrote:
> On Mon, 9 Nov 2015 01:59:06 -0500, rickman <gnu...@gmail.com> wrote:
>
>> I'm not familiar with automatic tuners that can tune the antenna while
>> in use.
>
> The basic benefits of having a remote controller are:
> 1. RF safety and you're not part of the antenna system.
> 2. A controller is easier to umm.... control.
> 3. Automatic remote tuning reacts to changes when you're not looking
> at the VSWR meter.
> 4. White knuckle tuning is difficult. Let the servos do the work.
> 5. It's the only effective way to tune a loop mounted on a tall pole,
> tower, or roof.

A remote controller is not an automatic tuner. Automatic implies the
controller tunes the resonance while a remote controller is just that, a
control to adjust the tuning remotely. I don't see how this could work
while transmitting. The tuning needs to be done separately.

>> One of the issues someone pointed out was that the dielectric
>> can heat up from the energy absorbed during transmission. Is an antenna
>> tuner real time in this case?
>
> Yes in receive. Probably not in transmit. In receive, you can tune
> all you want and nothing will explode or catch fire. In transmit, you
> can easily tune through full power and arc over the tuning capacitor.
> Auto tuning also goes through the optimum VSWR point several times
> during the tuning cycle. You transmitter may not like operating into
> a high VSWR load during tuning.

How does an automatic tuner operate? When you mention VSWR, how is that
affected by tuning?

> The solution is to tune at low tranmit power levels. Once the lowest
> VSWR point is found, you can increase your power. However, that
> usually prevents you from "tweaking" the tuning at full power, which
> is what you need to compensate for thermal drift. It's also difficult
> to tune with any modulation other than CW. I think (not sure) that
> some controllers have this ability, probably with warnings and
> disclaimers. I wouldn't trust it. Basically, to make it work
> requires a VWSR sensor and calculator that works when there's
> modulation, and a tuning capacitor that can tolerate moving while
> passing high currents. Arcing and welding the bearing and bushings
> might be a problem.
>
>> I crunched some numbers and found 100's of PPM change in tuned frequency
>> due to ambient temperature change over the course of a year for an
>> antenna with an air or vacuum tuning capacitor. I can find ceramic
>> dielectrics that would be lower than this and even in the opposite
>> direction to offset the natural drift. But I can't find this info for PEX.
>
> I looked and also didn't find anything. The problem is that you don't
> find tempco data for plumbing parts that were not intended to be used
> for RF components.

Substances have properties regardless of usage. PEX is not just used
for plumbing. It is also used in electrical cables where the dielectric
properties are very important.

>> I'm not terribly concerned with the actual value of Er and even the
>> dielectric strength. What is important to me is the temperature
>> coefficient of Er.
>
> Again, I think you might be trying to solve a problem that has already
> been solved by automatic tuning (which you need anyway). Unless you
> plan to transmit endlessly, you can simply press the tune button on
> the controller a few times per hour, and be done with trying to
> temperature stabilize the loop.

That's not how it was presented to me. The suggestion was that tuning
will change during transmission due to heating from the power being
transmitted. Of course that depends on not just the Er dependance with
temperature, but also the dissipation factor. So perhaps with material
of a sufficiently low DF the Er dependence on temperature is not so
important.

>> Interesting, but nearly every discussion I find on loop antennas has a
>> lot of fluff content.
>
> RF is magic. It's difficult to explain some things.

You mean people don't understand it. Anything that is understood can be
explained. If you don't understand it, you can't explain it. Even so,
that's not fluff. Fluff is when things are described in non-rigorous
ways like, "solder joints result in sub-optimum performance". Hard to
prove or disprove. Clearly they will have some effect even if that
effect too small to be measurable. "Sub-optimal" is pretty meaningless
in general until you define the details of "optimal".

>> Here is some from this discussion, "By the way
>> PEX is cross linked polyethylene and is superior to using sheet Teflon
>> in this instance." Unless the reason is stated for considering PEX
>> superior to Teflon, I haven't learned anything. I'm certainly not going
>> to take an anonymous person's word for it.
>
> The world is divided between practitioners of theory and of practice.
> Those who favor can explain anything, but can't build anything that
> actually works. Those that favor practice tend to build strange
> contraptions that they can't explain. That's also probably the main
> source of what you call "fluff". Sometimes, I run into a theoretician
> that knows which end of the soldering iron to grab, but they are rare.
> For the record, I'm a practitioner of practice, trial-n-error, and
> magic. I have difficulty explaining some things, and I think you've
> seen my horrid math.

I think the world is *not* divided at all, rather there is a range of
abilities on both theory and practice scales with independent values.
Fluff is fluff no mater what you are good at. If someone can't
recognize fluff, then they are missing a lot of understanding.

I'm used to seeing this sort of lack of rigor in many pursuits, cars,
sports, etc. I've also seen it in safety. Lots of people use seat of
the pants concepts in analyzing safety. It shows up very easily when
you simply ask questions about the source of the info. Same with the
amateur design of antennas. Lots of talk, but very little data in most
cases, like with solder joints.

>> I'm talking about water impacts. Humidity and rain soak into materials.
>> Some by absorption, others by infiltration into micro-cracks. I saw
>> some materials that talked about water trees in PEX. This is not a
>> universal problem in all plastics.
>
> I come from the marine radio part of the business. Water and
> corrosion are key parts of the marine radio problem. Many materials
> are hygroscopic and will absorb moisture. Apply some RF and the water
> boils out, as in a microwave oven. Do it too fast, and the material
> can crack. Of course, the tuning will change. Lots of info on
> plastics selection for minimal water absorption found online. For
> example:
> <http://www.curbellplastics.com/technical-resources/pdf/water-absorption-plastics.pdf>
> Polypropylene would be my first choice for minimal water absorption.
> However, it requires UV protection, which for RF applications means
> some kind of conformal coating. (Adding carbon black is a bad idea as
> it causes heating problems).

Plastic in a tuning capacitor should be protected from the elements in
other ways. Conformal coating is not really needed if the entire
capacitor is in a box, even a transparent plastic box as long as it
blocks the UV. Most plastics do.

>> There are simple facts about silver that make it only very
>> slightly better than copper for RF circuits. I know that you can
>> increase the size of the conductor by less than 5% as an alternative to
>> using silver plating if the electrical characteristics are the goal.
>> Can you explain why silver is required? The numbers don't show it.
>
> Antennas are mounted outdoors where exposed copper is an invitation to
> corrosion. If one must protect the copper with something, why not use
> silver, which also improves its RF characteristics?

My solution would be to use aluminum instead. Copper is not really
superior in a meaningful way and costs a lot more.

> My magloop nightmare come true:
> <http://www.mixw.co.uk/MagLoop/magloopF.htm>

I don't get your point here.


--

Rick

[amdx]

You can.
I don't think ultimate optimizing is for you.
Just make your coil with as much surface area as room will allow.
Then know it could have just a tiny bit less loss if you had the silver.
That tiny bit of loss will not be noticed in use, except for that little
nagging thought...

I once had a 6 or 7 turn loop made with 1/4" copper tubing*, Q was about
800 at 1MHz. I could have made it with 1/2" tubing, probably would have
had higher Q.
I guess the limits are money and how you want to limit physical size and
maximum inductance you can use. Did I miss any?
Mikek

*It had a vacuum variable mounted on it, I had it in the garage and my
young son moved it and broke the glass on the vacuum variable, it was a
sad day for me.

[amdx]

Money rears it's head as an issue, aluminum is cheaper.
+1 for aluminum.
Resistivity is 65% higher for aluminum.
I'd give that a -1, however, if maximizing Q is not
important in your design then still at +1.
Oxidation: Copper oxide vs Aluminum oxide.
Aluminum oxide is an insulator. How does that affect
skin resistance? I don't know, does it just shrink your tubing by the
thickness of the oxide?
Copper oxide is said to be a semiconductor, has much, much lower
resistance than aluminum oxide.
Page 5, > http://www.ets-lindgren.com/pdf/emctd_1293_weibler.pdf

Or just varnish it.
Bottom of page, > http://hamwaves.com/coils/en/


Aluminum is a great material to work with.

>> My magloop nightmare come true:
>> <http://www.mixw.co.uk/MagLoop/magloopF.htm>
>
> I don't get your point here.
>

Build one, monitor your dreams.

Jeff, I don't like the parallel sections,
seems like it could be made more complicated
using x, y, and z right angles. Nap on that! :-)


Mikek

[rickman]

On 11/10/2015 9:12 AM, amdx wrote:
> On 11/10/2015 1:41 AM, rickman wrote:
>> On 11/9/2015 12:08 PM, amdx wrote:
>
>>>>
>>> The silver is simply optimization. If you can make your coil wire 5%
>>> bigger, you should have already done that. Then if you want to optimized
>>> 1 + 0.05, silver plate it.
>>
>> Why can't you make the wire 5% bigger again? Where exactly is the cost?
>
> You can.
> I don't think ultimate optimizing is for you.
> Just make your coil with as much surface area as room will allow.
> Then know it could have just a tiny bit less loss if you had the silver.
> That tiny bit of loss will not be noticed in use, except for that little
> nagging thought...
>
> I once had a 6 or 7 turn loop made with 1/4" copper tubing*, Q was about
> 800 at 1MHz. I could have made it with 1/2" tubing, probably would have
> had higher Q.
> I guess the limits are money and how you want to limit physical size and
> maximum inductance you can use. Did I miss any?

People seem to go nuts with ideas that you need to optimize every little
thing without any evidence to show the significance of the impact on
performance. Your example is perfect. Increasing the copper tube from
1/4 inch to even just 3/8 inch would more than make up for silver
plating and not really cost that much more. There are guys who talk
about using single piece, 3 inch copper tube bent into a loop to avoid
having solder joints when using straight pieces even though those solder
joints will be about the same resistance as a quarter inch of the tube
or a microscopic increase in the resistance. Then they conveniently
forget about the resistance of the clamp connection to the vacuum
variable capacitor swamping out the solder joint resistance even more.

It makes me want to scream, "Enough of the maddness"!

--

Rick

[rickman]

On 11/10/2015 10:10 AM, amdx wrote:
> On 11/10/2015 2:02 AM, rickman wrote:
>> On 11/9/2015 7:52 PM, Jeff Liebermann wrote:
>
>>
>> My solution would be to use aluminum instead. Copper is not really
>> superior in a meaningful way and costs a lot more.
>>
>
> Money rears it's head as an issue, aluminum is cheaper.
> +1 for aluminum.
> Resistivity is 65% higher for aluminum.
> I'd give that a -1, however, if maximizing Q is not
> important in your design then still at +1.

I can overcompensate for the increased resistivity by using larger
tubing and still save $$$, +1 for aluminum. Resistivity is not resistance.

> Oxidation: Copper oxide vs Aluminum oxide.
> Aluminum oxide is an insulator. How does that affect
> skin resistance? I don't know, does it just shrink your tubing by the
> thickness of the oxide?

How many atoms is that in aluminum? So we are talking nanometers? I
started with a tube that is 100% larger, so still lower conductivity.

> Copper oxide is said to be a semiconductor, has much, much lower
> resistance than aluminum oxide.
> Page 5, > http://www.ets-lindgren.com/pdf/emctd_1293_weibler.pdf
>
> Or just varnish it.
> Bottom of page, > http://hamwaves.com/coils/en/
>
>
> Aluminum is a great material to work with.

The oxides are irrelevant.

--

Rick

[Jeff Liebermann]

On Tue, 10 Nov 2015 09:10:00 -0600, amdx <noj...@knology.net> wrote:

>>> My magloop nightmare come true:
>>> <http://www.mixw.co.uk/MagLoop/magloopF.htm>
>>
>> I don't get your point here.

1. It's not a fractal.
2. It's more like art than science.
3. It's a variation on my dryer vent hose antenna (tune by pounding).
4. It maximizes most of the worst characteristics of a loop, such as
high length to surface area = low Q, small capture area, and optimized
for low VSWR.
5. If you're worried about temperature drift, the lack of rigidity
should make it drift even more.

>Build one, monitor your dreams.

My ego is too inflated to fit into the loop. I'll stick with the
traditional colander on the head arrangement:
<https://www.google.com/search?q=colander+on+head&tbm=isch>

>Jeff, I don't like the parallel sections,
>seems like it could be made more complicated
>using x, y, and z right angles. Nap on that! :-)
> Mikek

Sorry, but everything I've built that involves a 4th dimension has
dissapeared when I applied power. The fields cancel and the entire
antenna is sucked into the resultant vortex.

Argh... I'm late again.

[amdx]

You want to see guys reaching for lowest losses, highest Q, follow a
crystal radio group.
Some there claim Q's of 2000, (I believe them) Using 2 and 3 parallel
pieces of 660/46 Litz wire. AMBCB.
The 2000Q thread; > http://tinyurl.com/q2hc6ga

More info, or a way to get to page two and three;

"Meanwhile, you can do the following search on Google:
site:www.midnightscience.com/rapntap/ 2000Q
If the main blue link doesn't work, then go down to the green link one
line below, and the little drop down menu at the right, and select
"cached" which will show you Google's cached copy of the page."

I didn't know that Google trick!


Recently a ferrite material out of China has made inductors hitting
1300 Q's easy. AMBCB
> http://theradioboard.com/rb/viewtopic.php?f=5&t=6259
Also rods of the same material.

Mikek

[rickman]

Crystal radio is a bit different. There your power source is the air
waves, so a higher Q makes a difference. When transmitting with a 96%
efficiency, using silver plating will only improve this to 96.2% at
very best. Not really useful and likely not measurable. Better to deal
with the significant losses like the extremely bad connection between
the vacuum variable cap and the loop. Straps???!!! Get real!

--

Rick

[rickman]

On 11/10/2015 12:17 PM, Jeff Liebermann wrote:
> On Tue, 10 Nov 2015 09:10:00 -0600, amdx <noj...@knology.net> wrote:
>
>>>> My magloop nightmare come true:
>>>> <http://www.mixw.co.uk/MagLoop/magloopF.htm>
>>>
>>> I don't get your point here.
>
> 1. It's not a fractal.
> 2. It's more like art than science.
> 3. It's a variation on my dryer vent hose antenna (tune by pounding).
> 4. It maximizes most of the worst characteristics of a loop, such as
> high length to surface area = low Q, small capture area, and optimized
> for low VSWR.
> 5. If you're worried about temperature drift, the lack of rigidity
> should make it drift even more.

But you don't really know the details of how it works, so you don't know
how well it can work other than by building it and testing. I haven't
seen any reports that can be considered rigorous, but there is plenty of
enthusiasm by the users. They think these antennas work well.

>> Build one, monitor your dreams.
>
> My ego is too inflated to fit into the loop. I'll stick with the
> traditional colander on the head arrangement:
> <https://www.google.com/search?q=colander+on+head&tbm=isch>

Are you making fun of religion now?

>> Jeff, I don't like the parallel sections,
>> seems like it could be made more complicated
>> using x, y, and z right angles. Nap on that! :-)
>> Mikek
>
> Sorry, but everything I've built that involves a 4th dimension has
> dissapeared when I applied power. The fields cancel and the entire
> antenna is sucked into the resultant vortex.
>
> Argh... I'm late again.

Someday you'll be late for the last time and everyone will call you "late".

--

Rick

[John S]

I'm curious about the 2000 Q restricting bandwidth. At 1MHz, the
bandwidth would be only 500Hz. Does that affect the quality of the
audio? That is, does it sound very bass-y?

[Jeff Liebermann]

On Tue, 10 Nov 2015 16:09:51 -0500, rickman <gnu...@gmail.com> wrote:

>But you don't really know the details of how it works, so you don't know
>how well it can work other than by building it and testing.

I can get a clue on how well it works from an NEC2 model. However,
this loop is easy. Remember your complaints about the relative merits
of a circular loop, octagonal loop, square, and triangular loop? Well,
this contrivance is a good example of a very shrunken loop, where the
area enclosed by the loop has been minimized.

Anyway, I'm a big fan of building something just to see what happens.
It's part of "Learn by Destroying".

>I haven't
>seen any reports that can be considered rigorous, but there is plenty of
>enthusiasm by the users. They think these antennas work well.

Yep. I also read the reviews on various products and usually find a
few fanatics that will defend inferior junk to the death. It happens.
However, I'm not talking about "these" antennas as in all types of
loop antennas. I'm talking about this particular loop:
<http://www.mixw.co.uk/MagLoop/magloopF.htm>

>> My ego is too inflated to fit into the loop. I'll stick with the
>> traditional colander on the head arrangement:
>> <https://www.google.com/search?q=colander+on+head&tbm=isch>
>
>Are you making fun of religion now?

I'm Jewish and occasionally wear a yarmulke (keepah or skull cap)
which entitles me to some liberties in their design and operation.
Full disclosure: Mine is not lined with tin foil.

>> Argh... I'm late again.
>
>Someday you'll be late for the last time and everyone will call you "late".

Actually, I try to always be on time or a little early. In this case,
it was for a ritual morning exercise trudge through the local state
park. We usually have a small group that I didn't want to keep
waiting.

[Jeff Liebermann]

On Tue, 10 Nov 2015 11:40:43 -0600, amdx <noj...@knology.net> wrote:

>You want to see guys reaching for lowest losses, highest Q, follow a
>crystal radio group.
>Some there claim Q's of 2000, (I believe them) Using 2 and 3 parallel
>pieces of 660/46 Litz wire. AMBCB.
>The 2000Q thread; > http://tinyurl.com/q2hc6ga

That's the unloaded Q measured in an HP4342A Q meter. Putting a load
across the coil will drop the Q considerably.

The equivalent parallel resistor across a perfect 120uHy inductor and
resonating capacitor are:

R = Q * 2*Pi*f*L
R = 2000 * 2 * 3.14 * 1*10^6 * 120*10^-6
R = 1.5Meg

So, all it would take is a 1.5Meg load across the parallel coil and
capacitor, and the Q would get cut in half. That doesn't sound very
practical.

I used an HP4342A at a former employer. Nice machine but really
unstable for high-Q measurements. I'm not surprised that he had to
leave it running for a while to stabilize:
<http://www.radiomuseum.org/r/hewlett_pa_q_meter_4342a4342.html>
$300 to $500 on eBay. Ouch.

Drivel: The MFJ-259a is now fixed. It was the usual blown diodes,
along with cleaning up the mess left by the leaky batteries.

[rickman]

At 60 kHz the bandwidth would be 30 Hz, perfect! Great SNR improvement.

--

Rick

[rickman]

On 11/10/2015 7:37 PM, Jeff Liebermann wrote:
> On Tue, 10 Nov 2015 16:09:51 -0500, rickman <gnu...@gmail.com> wrote:
>
>> But you don't really know the details of how it works, so you don't know
>> how well it can work other than by building it and testing.
>
> I can get a clue on how well it works from an NEC2 model. However,
> this loop is easy. Remember your complaints about the relative merits
> of a circular loop, octagonal loop, square, and triangular loop? Well,
> this contrivance is a good example of a very shrunken loop, where the
> area enclosed by the loop has been minimized.

That is an assumption since you are analyzing it as a simple, circular
loop which it is not. NEC2 may or may not be adequate to model it.
Someone posted that they get significantly different results from two
different simulators under some conditions.

> Anyway, I'm a big fan of building something just to see what happens.
> It's part of "Learn by Destroying".
>
>> I haven't
>> seen any reports that can be considered rigorous, but there is plenty of
>> enthusiasm by the users. They think these antennas work well.
>
> Yep. I also read the reviews on various products and usually find a
> few fanatics that will defend inferior junk to the death. It happens.
> However, I'm not talking about "these" antennas as in all types of
> loop antennas. I'm talking about this particular loop:
> <http://www.mixw.co.uk/MagLoop/magloopF.htm>
>
>>> My ego is too inflated to fit into the loop. I'll stick with the
>>> traditional colander on the head arrangement:
>>> <https://www.google.com/search?q=colander+on+head&tbm=isch>
>>
>> Are you making fun of religion now?
>
> I'm Jewish and occasionally wear a yarmulke (keepah or skull cap)
> which entitles me to some liberties in their design and operation.
> Full disclosure: Mine is not lined with tin foil.

I'm referring to the Pastafarians of which I am a member.

>>> Argh... I'm late again.
>>
>> Someday you'll be late for the last time and everyone will call you "late".
>
> Actually, I try to always be on time or a little early. In this case,
> it was for a ritual morning exercise trudge through the local state
> park. We usually have a small group that I didn't want to keep
> waiting.

I mean "late as in *the late* Dentarthurdent".

--

Rick

[amdx]

Jeff explained the loading, but I'll add, the rest of the circuitry to
extract the audio signal and drive the headphones to create sound drops
the Q. It can be as bad as a 2000 ohm headphone or as good as a
transformer with very high input impedance, over 1.5 Megaohms according
to Ben Tongue.

> http://www.bentongue.com/xtalset/5hpXform/5hpXform.html

All 29 of his crystal radio research papers are here.

> http://www.bentongue.com/xtalset/xtalset.html

Tremendous resource for Crystal Radio devotees.
Mikek

[amdx]

Where did you get 96% efficient?

From the site below.
"The efficiency of a magnetic loop antenna is typically calculated as
(Smith, 2006);

efficiency=Rr/(Rr+Rhf2)

Rr=radiation resistance (ohms)

Rhf2=RF losses from combined skin effect and proximity effect (ohms)

This term is not adjusted for the effects of ground or nearby objects."


This builder has a different design.

> http://gridtoys.com/glen/loop/loop3.html

You'll enjoy this line on his page.

"*Aluminum works well in magnetic loop antennas. Yes, pure copper is a
little better, but in multiple conductor magnetic loop antennas, there
may be difficulty getting a copper loop to support its own weight.
Structurally, aluminum is a lot better. Just make the conductors bigger."

Mikek

[rickman]

On 11/11/2015 6:59 AM, amdx wrote:
> On 11/10/2015 2:36 PM, rickman wrote:
>> On 11/10/2015 12:40 PM, amdx wrote:
> When transmitting with a 96%
>> efficiency, using silver plating will only improve this to 96.2% at
>> very best. Not really useful and likely not measurable. Better to deal
>> with the significant losses like the extremely bad connection between
>> the vacuum variable cap and the loop. Straps???!!! Get real!
>>
>
> Where did you get 96% efficient?

PFA It is an example of an efficient loop. Work with a less efficient
loop and the sliver still makes only a small difference, less than the
raw 5% difference in conductivity.

> From the site below.
> "The efficiency of a magnetic loop antenna is typically calculated as
> (Smith, 2006);
>
> efficiency=Rr/(Rr+Rhf2)
>
> Rr=radiation resistance (ohms)
>
> Rhf2=RF losses from combined skin effect and proximity effect (ohms)
>
> This term is not adjusted for the effects of ground or nearby objects."

Your point?

BTW, Rhf2 I believe is intended to be the resistive losses after
considering the skin and proximity effects. As you can see, a 5%
difference in Rhf2 will be less than 5% in the efficiency and depending
on the numbers, much less.

If you are working at very low efficiencies, then yes, a 5% difference
in Rhf2 will result in a noticeable difference in efficiency, but this
would be improved much more by using a good design rather than a poor
one. Silver plating a crap antenna will still give you a crap antenna.

> This builder has a different design.
>
>> http://gridtoys.com/glen/loop/loop3.html
>
> You'll enjoy this line on his page.
>
> "*Aluminum works well in magnetic loop antennas. Yes, pure copper is a
> little better, but in multiple conductor magnetic loop antennas, there
> may be difficulty getting a copper loop to support its own weight.
> Structurally, aluminum is a lot better. Just make the conductors bigger."

Not sure what he is talking about. He seems to have screwed up the
formulas calcuating the skin effect. I can't reconcile his math.

--

Rick

[viron...@yahoo.com]

You analysis of the accordion roughness' effect is relative to the wavelength. I have no idea of the relationship, but my brother whom has designed antenna systems for military aircraft and patented antenna designs schooled on the fact that the formulas we all love and use are WRONG!

However, the formulas we use work well because we typically use relatively thin radiating elements compared to the wavelength, often significantly less than 1% of the operating frequency. The correct formula is surface area of the radiating element NOT LENGTH.

To you and I building wire, Yagi, and loop antenna with skinny radiating elements length ends up being very close to the surface area. However, design an antenna for a cellphone from a thin plate or part of an aircraft fuselage and the length formula starts falling apart, especially at the higher frequencies.

I didn't bother learning the correct formula as it is a little more complex. I think it may come up when you start building fractal shaped antennas, such as were used in WWII by underground operatives using the lead frames stained glass windows in churches as radiating elements. The surface area formula may become relavent to magnetic loops with radiating loops with very thick radiators.

N4VEP