On 11/9/2015 12:59 AM, rickman wrote:
On 11/8/2015 10:46 PM, Jeff Liebermann wrote:
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.

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.

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

On 11/9/2015 12:08 PM, amdx wrote:
On 11/9/2015 12:59 AM, rickman wrote:
On 11/8/2015 10:46 PM, Jeff Liebermann wrote:
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.

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.

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?

--

Rick

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?
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.

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

On 11/10/2015 9:30 AM, rickman wrote:
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"!


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

On 11/10/2015 12:40 PM, amdx wrote:
On 11/10/2015 9:30 AM, rickman wrote:
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"!


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.

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

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?

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

On 11/10/2015 11:40 AM, amdx wrote:
On 11/10/2015 9:30 AM, rickman wrote:
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"!


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

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?

On 11/10/2015 5:55 PM, John S wrote:
On 11/10/2015 11:40 AM, amdx wrote:

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

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?

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

--

Rick

On 11/10/2015 4:55 PM, John S wrote:
On 11/10/2015 11:40 AM, amdx wrote:
On 11/10/2015 9:30 AM, rickman wrote:
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"!


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

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 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