On 11/8/2015 10:23 PM, Jeff Liebermann wrote:
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 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

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.

--

Rick

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 Mon, 9 Nov 2015 01:59:06 -0500, rickman wrote:

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

The basic benefits of having a remote controller a
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



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

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 11/9/2015 7:52 PM, Jeff Liebermann wrote:
On Mon, 9 Nov 2015 01:59:06 -0500, rickman wrote:

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

The basic benefits of having a remote controller a
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

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 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.
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

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 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