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Old November 4th 15, 04:42 PM posted to rec.radio.amateur.antenna
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On 11/4/2015 8:52 AM, Ian Jackson wrote:
In message , John S
writes
On 11/4/2015 6:49 AM, Ian Jackson wrote:
In message , rickman
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?



Yes. But, is it measurable?


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


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

--

Rick

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Old November 4th 15, 10:42 PM posted to rec.radio.amateur.antenna
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In message , rickman
writes
On 11/4/2015 8:52 AM, Ian Jackson wrote:
In message , John S
writes
On 11/4/2015 6:49 AM, Ian Jackson wrote:
In message , rickman
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?



Yes. But, is it measurable?


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


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

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
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Old November 6th 15, 02:40 AM posted to rec.radio.amateur.antenna
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On Wed, 4 Nov 2015 00:17:11 -0500, rickman wrote:

On 11/2/2015 7:39 PM, Jeff Liebermann wrote:
On Mon, 2 Nov 2015 09:13:38 -0600, amdx 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).
--
Jeff Liebermann
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
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Old November 6th 15, 05:23 PM posted to rec.radio.amateur.antenna
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On 11/5/2015 8:40 PM, Jeff Liebermann wrote:
On Wed, 4 Nov 2015 00:17:11 -0500, rickman wrote:

On 11/2/2015 7:39 PM, Jeff Liebermann wrote:
On Mon, 2 Nov 2015 09:13:38 -0600, amdx 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
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Old November 8th 15, 09:44 PM posted to rec.radio.amateur.antenna
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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%20Ant enna_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
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558


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Old November 8th 15, 11:14 PM posted to rec.radio.amateur.antenna
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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).

--
Jeff Liebermann
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
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Old November 9th 15, 12:02 AM posted to rec.radio.amateur.antenna
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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%20Ant enna_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
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Old November 9th 15, 01:12 AM posted to rec.radio.amateur.antenna
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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
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Old November 9th 15, 04:23 AM posted to rec.radio.amateur.antenna
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Default Flex dryer vent hose loop antenna

On Sun, 8 Nov 2015 18:02:19 -0500, rickman 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%20Ant enna_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 ****es 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
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
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Old November 9th 15, 04:46 AM posted to rec.radio.amateur.antenna
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Default Flex dryer vent hose loop antenna

On Sun, 8 Nov 2015 19:12:38 -0500, rickman 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.


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


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