On Sun, 1 Nov 2015 14:57:36 -0500, rickman wrote:


Short summary:
1. DC resistance does not change with soldering.
2. Temp and mechanical stability of the loop is greatly improved by
soldering and welding. The stronger the joint, the more stable.
3. Soldering did not seem to affect the Q of the loop, although my
method was rather sloppy and results uncertain.

That's a lot more clear, but why do you say the "temp" stability of the
loop was improved?

Sorry. Temp stability should not be included.

silver plated antennas

That would be a lot of work for a 12 foot tall antenna even if not
terribly expensive, for very little gain, about 5% conductivity which is
cut in half by the skin effect. Do you really want to go to all that
trouble for a 2.5% improvement when you can just use copper with a 2.5%
larger OD to achieve the same benefit?

Hams have spend considerably more money of smaller improvements. I
keep seeing HF antennas fed by 7/8" Heliax and wondering about the
size of the owners bank account. Anything for that last tenth of a
decibel. Considering the cost of monster towers, lowest possible loss
coax, digital everything, and strange looking antennas, I see silver
plating as a trivial expense.

Larger diameter tubing is probably a good alternative. I initially
played with a loop made from a length of RG-8/u coax cable. When I
found that the resistance of the braid was a problem, I switched to
RG-214/u (silver plated double braid). That worked much better, but
the higher Q now made mechanical rigidity an issue. So, I tried a
length of 9913, which was stiffer, but lacked the improved
conductivity of the silver plated double shielded braid. After that,
I tried a chunk of unlabeled CATV 75 ohm semi-rigid coax about 3/4"
diameter. The conductivity of the aluminum was lousy, but the
mechanical rigidity was great. There were also some marginal efforts
using Hula Hoops, aluminized duct tape, and Litz wire antennas (25
pair of #24 awg insulated telco wires). Incidentally, besides the
usual OTA (over the air) testing, I used the measured Q as a figure of
merit on the assumption that higher Q means lower losses.

Really? You want to design a copper antenna with series capacitors
scattered in your loop?

Nope. The press fit copper overlap is sufficient to make a tolerable
connection. The problem is that it's not a perfect connection, so
anything that moves will affect the tuning. If overlapping copper
didn't work, then all the coaxial connectors also wouldn't work.

Yes, it would not just affect the tuning, but
the tuning range and vary with all sorts of changes like temperature and
humidity. That strikes me as a crazy way to build an antenna.

Yep. I hadn't planned to sell the antenna in that condition. I was
doing the same thing as the author of the article. I was testing the
antenna before soldering everything permanently in place to allow for
easier tweaking and adjusting.

The skin effect of different materials seems to be current issue:
http://owenduffy.net/calc/SkinDepth.htm
Looks like the higher resistivity of 63/37 solder, compared to copper,
required more skin depth. Adding some silver to the solder should fix
that.

I don't know what "required more skin depth" implies. I have yet to
find a conductor that wasn't thick enough to provide 95% of the max
potential conductivity down to 70 kHz. The skin depth goes by the
square root of the resistivity, so there is minimal difference because
of that.

It's not the conductor. It's the plating thickness. I get into that
quite a bit with PIM (passive intermodulation) where the two
dissimilar metals create a diode junction and produce a mixing action.
Anyway, the idea is to make the plating thickness thick enough so that
all the RF is concentrated in the plating, and not distributed into
the base metal. As I recall, the calculated skin depth is roughly
where 63% of the RF is concentrated in the outer part of the conductor
down to the skin depth. In order to get that closer to something like
90%, you need 3 skin depth thickness. If you want to take advantage
of silver plating, it needs to be plated where the RF is moving.

So even if the solder if four times more
resistive it will be swamped by the 100's of times greater length of
copper.
(...)
The solder inside the
overlap would be inconsequential other than mechanical support.

Agreed. The only place where the solder might have an effect is on
mechanical rigidity. The small amounts used, even for a square loop
assembled from sections, it trivial compared to the losses in the
areas affected by skin effect. However trivial, it's not zero. I
suggest that you run the spreadsheet at:
http://www.aa5tb.com/aa5tb_loop_v1.22a.xls
and plug in various numbers for added resistance of the solder. The
numbers are tiny, but they will produce a noticeable change in Q and
therefore efficiency.

I have no idea why you think soldered joint would have poor electrical
stability.

Because solder is soft compared to copper pipe. I don't know the
mechanism involved, but when I assembled a loop from pieces and used
it as a receive antenna, I found myself constantly retuning the loops.
I later put it on a sweeper and a return loss bridge and noticed that
the tuning was changing a little as the antenna was tapped with a
stick. I couldn't tell exactly what was causing the tuning change
because everything was moving. When I later soldered the antenna
together (using 60/40 solder), it was much more mechanically stable in
receive but still not perfect. The only thing loose was the coax
connector. At that point, I stopped tinkering and tried it on the air
at 5 and later 50 watts. Even if I did nothing to the antenna, it had
to retune it every 15 minutes or so. A similar loop (but somewhat
larger) where I had the local mechanical contractor bend into a loop,
didn't have these problems and only required retuning when the
temperature changed, or when I changed in frequency. I might have
missed some factor, but it would seem to me that the use of solder was
the only major difference between the loops. (Incidentally, the
various coax cable loops were worse than the soldered pipe section
loop and were only useable because the Q was lower and therefore had a
wider operating bandwidth).

Why would I want the silver to be as thick as the skin depth?

Because the RF goes through the outside of the conductor. Better to
have it silver, with its slightly better conductivity, than ordinary
solder. If I could silver plate the solder, just like the copper, I
probably would.

I have no interest in plating copper on zinc on aluminum. If I can do
silver that seems like the way to go.

With copper plating on the ends of the aluminum pipes, you can solder
them together. Of course, you could also weld aluminum pipes
together, so that's not a big advantage except to attach coax
connectors and tuning caps.

Personally, I think you're overdoing it and are hung up on minutiae
and detail. Optimizing the loop resistance to the last remaining
decimal point might be useful after you have a reproducible initial
design, or if you're trying to build the ultimate magnetic loop
antenna. However, the various dimensional aspects of the design are
far more important. How big a loop? How to match it to 50 ohms?
What's the takeoff angle? Tuning range and bandwidth? Start he
http://www.aa5tb.com/loop.html
http://www.aa5tb.com/aa5tb_loop_v1.22a.xls
See Note 2.

I'm trying to identify significant issues and the easy steps to mitigate
them. If it is not clear how significant an issue is, but the step to
mitigate it is easy, then why not do it.

Fair enough. Permit me to offer a suggestion. Please state your
objective when you begin asking questions. Most of your postings
appear to be target practice aimed at the comments of the poster. It
often feels like a duck shoot, where you take shots at anything that
fly by. Your points are usually well taken, but totally aimless
unless you state what you are trying to accomplish. For example, you
haven't indicated if you plan to actually build an antenna, have built
an antenna, are having problems with an antenna, or simply want to
understand the technology from an academic point of view. The type of
replies vary with the intent. I was very interested in your LTspice
model of a loop antenna, but on which I do not consider myself
qualified to comment. However, when it comes to construction and
testing, I can supply some help.

I can't see *not* soldering the connections. The tuning capacitor will
be aluminum. To avoid connections between different metals the entire
unit will be aluminum. So I will need to solder the aluminum unless it
is easier to weld which I'm pretty sure is not the case. I think the
silver plating and silver solder is the short and easy path to an
optimum solution with low cost. But the jury is still out.

Have you considered copper or brass butterfly capacitors?
http://files.qrz.com/a/ab1pa/IMG_2964.JPG
I suspect that there are kits available in brass. The benefits of
soldering the rotor plates to the center shaft is well worth trying
copper. In an ordinary variable cap, any series resistance between
the plates and their connecting rod is going to cause problems. One
reason why butterfly caps are preferred is because they eliminate any
losses in the rotor plate to center shaft (at the price of half the
capacitance).




--
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 11/1/2015 10:59 PM, Jeff Liebermann wrote:
On Sun, 1 Nov 2015 14:57:36 -0500, rickman wrote:


Short summary:
1. DC resistance does not change with soldering.
2. Temp and mechanical stability of the loop is greatly improved by
soldering and welding. The stronger the joint, the more stable.
3. Soldering did not seem to affect the Q of the loop, although my
method was rather sloppy and results uncertain.

That's a lot more clear, but why do you say the "temp" stability of the
loop was improved?

Sorry. Temp stability should not be included.

silver plated antennas

That would be a lot of work for a 12 foot tall antenna even if not
terribly expensive, for very little gain, about 5% conductivity which is
cut in half by the skin effect. Do you really want to go to all that
trouble for a 2.5% improvement when you can just use copper with a 2.5%
larger OD to achieve the same benefit?

Hams have spend considerably more money of smaller improvements. I
keep seeing HF antennas fed by 7/8" Heliax and wondering about the
size of the owners bank account. Anything for that last tenth of a
decibel. Considering the cost of monster towers, lowest possible loss
coax, digital everything, and strange looking antennas, I see silver
plating as a trivial expense.

I didn't say anything about cost. I said trouble.


Larger diameter tubing is probably a good alternative. I initially
played with a loop made from a length of RG-8/u coax cable. When I
found that the resistance of the braid was a problem, I switched to
RG-214/u (silver plated double braid). That worked much better, but
the higher Q now made mechanical rigidity an issue. So, I tried a
length of 9913, which was stiffer, but lacked the improved
conductivity of the silver plated double shielded braid. After that,
I tried a chunk of unlabeled CATV 75 ohm semi-rigid coax about 3/4"
diameter. The conductivity of the aluminum was lousy, but the
mechanical rigidity was great. There were also some marginal efforts
using Hula Hoops, aluminized duct tape, and Litz wire antennas (25
pair of #24 awg insulated telco wires). Incidentally, besides the
usual OTA (over the air) testing, I used the measured Q as a figure of
merit on the assumption that higher Q means lower losses.

A larger diameter loop is a great way to go. Radiation resistance goes
up with the 4th power of radius while the dissipative resistance goes up
by linearly, greatly increasing the efficiency.

Larger diameter tubing is good way to reduce the dissipative resistance,
as long as you can afford it or can work with it. The tubing isn't so
pricy, but I've seen that joints cost as much as a 10 foot piece. I
haven't checked that myself. The perception of many is that joints are
bad, so they will want to bend the tubing to form a circle, this gets to
be hard with larger diameter tubing. I'm ok with an octagon (only
loosing 5% of the area of a circle with the same circumference) or maybe
even a square Which looses about 21% of the area. In terms of radiation
resistance these impacts should be squared to give 90% and 62% of the
radiation resistance. The square is easier to make, but the octagon in
addition to being half again more efficient, has a certain panache
compared to a square. I need to find out just how much unions are for
large diameter tubing.


Really? You want to design a copper antenna with series capacitors
scattered in your loop?

Nope. The press fit copper overlap is sufficient to make a tolerable
connection. The problem is that it's not a perfect connection, so
anything that moves will affect the tuning. If overlapping copper
didn't work, then all the coaxial connectors also wouldn't work.

There is a *big* difference between a precision machined connector and
concentric copper tubes. Heck, there is a big difference between
quality connectors and cheap ones!!! Besides, a coax connector isn't
designed to pass such high currents as a tuned loop antenna. Try
putting those in your loop and I bet it fails very quickly.


Yes, it would not just affect the tuning, but
the tuning range and vary with all sorts of changes like temperature and
humidity. That strikes me as a crazy way to build an antenna.

Yep. I hadn't planned to sell the antenna in that condition. I was
doing the same thing as the author of the article. I was testing the
antenna before soldering everything permanently in place to allow for
easier tweaking and adjusting.

When constructing a loop antenna of copper or aluminum tubing, what is
there to tweak that would be easier with unsoldered joints?


The skin effect of different materials seems to be current issue:
http://owenduffy.net/calc/SkinDepth.htm
Looks like the higher resistivity of 63/37 solder, compared to copper,
required more skin depth. Adding some silver to the solder should fix
that.

I don't know what "required more skin depth" implies. I have yet to
find a conductor that wasn't thick enough to provide 95% of the max
potential conductivity down to 70 kHz. The skin depth goes by the
square root of the resistivity, so there is minimal difference because
of that.

It's not the conductor. It's the plating thickness. I get into that
quite a bit with PIM (passive intermodulation) where the two
dissimilar metals create a diode junction and produce a mixing action.
Anyway, the idea is to make the plating thickness thick enough so that
all the RF is concentrated in the plating, and not distributed into
the base metal. As I recall, the calculated skin depth is roughly
where 63% of the RF is concentrated in the outer part of the conductor
down to the skin depth. In order to get that closer to something like
90%, you need 3 skin depth thickness. If you want to take advantage
of silver plating, it needs to be plated where the RF is moving.

3 skin depths gets you 95% of the conductivity. But the context isn't
making any sense. Copper tubing and solder joints. What are you
planning to plate to get 3 skin depths, the entire copper tube? I'm lost.

In my thinking you need to minimize the use of solder and keep it to as
small an area as possible. Because of the skin effect it will impact
any surface it is on the outside of. So get rid of it or don't use it
in the first place. Or use a very high silver content solder.


So even if the solder if four times more
resistive it will be swamped by the 100's of times greater length of
copper.
(...)
The solder inside the
overlap would be inconsequential other than mechanical support.

Agreed. The only place where the solder might have an effect is on
mechanical rigidity. The small amounts used, even for a square loop
assembled from sections, it trivial compared to the losses in the
areas affected by skin effect. However trivial, it's not zero. I
suggest that you run the spreadsheet at:
http://www.aa5tb.com/aa5tb_loop_v1.22a.xls
and plug in various numbers for added resistance of the solder. The
numbers are tiny, but they will produce a noticeable change in Q and
therefore efficiency.

I think that is a pretty bogus statement. Using the default numbers in
the spreadsheet I could add up to 0.1 mohms before it even changed the Q
factor in the 4th significant digit. The formulas seem to be locked, so
I can't tell what is being done, but I assume the "added loss" is just
added to the loss resistance formula shown on the "formulas" sheet.

Tube thickness of 40 mils. Resistivity (rho) around 1.5 * 10^-7 ohm-m.
Tube diameter of 2 inches. Assume the solder forms a triangular fillet
in the L at the end of the overlap. Length of the hypotenuse is 56
mils. So change the triangle into a rectangle of half that length 28
mil and 28 mil high (max thickness from hypotenuse to right angle
corner). So the resistance will be...

I'm not sure this ascii art will help, lol.

---------,./.
| | \ .
| | \ . 56mil
40mil | \ .
| | \ .
| | \ .
---------' \ /
--------------------------
|-40mil-|

R = rho * L / ( W * H ) = 1.5e-7 ohm-m * 0.712 mm / (0.712 mm * 50.8
mm) = 3 micro-ohms. Yes, MICRO ohms.


I have no idea why you think soldered joint would have poor electrical
stability.

Because solder is soft compared to copper pipe. I don't know the
mechanism involved, but when I assembled a loop from pieces and used
it as a receive antenna, I found myself constantly retuning the loops.
I later put it on a sweeper and a return loss bridge and noticed that
the tuning was changing a little as the antenna was tapped with a
stick. I couldn't tell exactly what was causing the tuning change
because everything was moving. When I later soldered the antenna
together (using 60/40 solder), it was much more mechanically stable in
receive but still not perfect. The only thing loose was the coax
connector. At that point, I stopped tinkering and tried it on the air
at 5 and later 50 watts. Even if I did nothing to the antenna, it had
to retune it every 15 minutes or so. A similar loop (but somewhat
larger) where I had the local mechanical contractor bend into a loop,
didn't have these problems and only required retuning when the
temperature changed, or when I changed in frequency. I might have
missed some factor, but it would seem to me that the use of solder was
the only major difference between the loops. (Incidentally, the
various coax cable loops were worse than the soldered pipe section
loop and were only useable because the Q was lower and therefore had a
wider operating bandwidth).

Unexplained issues are not really proof. Someone in another group has a
coax antenna that detunes with temperature. I should ask him if it
detunes with time or just temperature. His frequency drift is some 20
times larger than I can explain with the expansion of the materials in
the capacitor and the loop. Since he is using the coax which is very
flexible, maybe the plastics involved are causing a dimensional change
large than would be seen for solid metal???

Solder may be softer than copper, but it is hard to explain how a solder
joint would change the length of the tubing by enough to cause a detune.


Why would I want the silver to be as thick as the skin depth?

Because the RF goes through the outside of the conductor. Better to
have it silver, with its slightly better conductivity, than ordinary
solder. If I could silver plate the solder, just like the copper, I
probably would.

I've lost context here. Silver only gives a 2.5% improvement in
conductivity when accounting for skin depth. This is pointless really.
I don't know where this silver is supposed to be, but the sliver
plating I am talking about will be the surface the solder adheres to, so
it would be *under* the solder, not on top of it. I am only considering
using it because it is very hard to solder aluminum unless it is plated.
I'm not trying to improve conductivity at all. If I want better
conduction, I'll use a larger diameter aluminum tube.


I have no interest in plating copper on zinc on aluminum. If I can do
silver that seems like the way to go.

With copper plating on the ends of the aluminum pipes, you can solder
them together. Of course, you could also weld aluminum pipes
together, so that's not a big advantage except to attach coax
connectors and tuning caps.

I can solder the silver plating which is why I'm doing it.


Personally, I think you're overdoing it and are hung up on minutiae
and detail. Optimizing the loop resistance to the last remaining
decimal point might be useful after you have a reproducible initial
design, or if you're trying to build the ultimate magnetic loop
antenna. However, the various dimensional aspects of the design are
far more important. How big a loop? How to match it to 50 ohms?
What's the takeoff angle? Tuning range and bandwidth? Start he
http://www.aa5tb.com/loop.html
http://www.aa5tb.com/aa5tb_loop_v1.22a.xls
See Note 2.

I'm trying to identify significant issues and the easy steps to mitigate
them. If it is not clear how significant an issue is, but the step to
mitigate it is easy, then why not do it.

Fair enough. Permit me to offer a suggestion. Please state your
objective when you begin asking questions. Most of your postings
appear to be target practice aimed at the comments of the poster. It
often feels like a duck shoot, where you take shots at anything that
fly by. Your points are usually well taken, but totally aimless
unless you state what you are trying to accomplish. For example, you
haven't indicated if you plan to actually build an antenna, have built
an antenna, are having problems with an antenna, or simply want to
understand the technology from an academic point of view. The type of
replies vary with the intent. I was very interested in your LTspice
model of a loop antenna, but on which I do not consider myself
qualified to comment. However, when it comes to construction and
testing, I can supply some help.

Sorry if my comments feel like pot shots. That is not my goal. I am
trying to understand what is being said. To be honest, a lot of your
comments seem to wander and not connect to what I have posted or even to
what you have stated elsewhere in the post or thread. This is probably
because I'm not picturing fully the ideas you have.

To respond to your request, initially my interest was basically
academic, but as I hear more seat of the pants info from experienced
people I am more interested in finding out what really works and what
doesn't which means I'll have to build my own.

Did I ever send you my spice model? I haven't done anything with it in
a long time. It was a receiving antenna. One point I understand better
now is the radiation resistance which I could add in a calculation for.
Initially someone gave me a number I used. But for the small loop I
was looking at and the very low frequency (60 kHz) the radiation
resistance would be very tiny and so not really a factor.


I can't see *not* soldering the connections. The tuning capacitor will
be aluminum. To avoid connections between different metals the entire
unit will be aluminum. So I will need to solder the aluminum unless it
is easier to weld which I'm pretty sure is not the case. I think the
silver plating and silver solder is the short and easy path to an
optimum solution with low cost. But the jury is still out.

Have you considered copper or brass butterfly capacitors?
http://files.qrz.com/a/ab1pa/IMG_2964.JPG
I suspect that there are kits available in brass. The benefits of
soldering the rotor plates to the center shaft is well worth trying
copper. In an ordinary variable cap, any series resistance between
the plates and their connecting rod is going to cause problems. One
reason why butterfly caps are preferred is because they eliminate any
losses in the rotor plate to center shaft (at the price of half the
capacitance).

I want to build this from scratch if I do it. I don't see a problem
with aluminum. I can't see the benefit of soldering the rotor plates.
So far no one has been able to explain how there would be any difference
in voltage except for very small values. If I felt the need to connect
them I would likely silver plate and solder rather than weld. But your
findings above with the lack of stability concern me with soldering, at
least in the main loop.

--

Rick

On Mon, 2 Nov 2015 00:16:42 -0500, rickman wrote:

Short replies... It's Monday and the phone is ringing.

There is a *big* difference between a precision machined connector and
concentric copper tubes. Heck, there is a big difference between
quality connectors and cheap ones!!! Besides, a coax connector isn't
designed to pass such high currents as a tuned loop antenna. Try
putting those in your loop and I bet it fails very quickly.

I'm using the shield connection, not the center conductor. The center
pin will probably be destroyed by the high currents and from arcing
due to high voltages. If crimped, the shield will probably survive.
If I wanted to prove it, I would calculate the square mils of surface
contact area for the shield in the connector. Overlapping CLEAN
copper 3/4" tubing makes a tolerable coax connector with the addition
of slots and a hose clamp for compression. I've seen Cu plumbing
parts used as welding cable connectors.

When constructing a loop antenna of copper or aluminum tubing, what is
there to tweak that would be easier with unsoldered joints?

The lengths of various sections so that the tuning range of the
capacitor works as planned. My first plumbing loop was calculated for
a loop circumference based on the center line of the plumbing. I had
forgotten to include the length of the capacitor stator frame in the
loop length. I also found that the location where I attached my
tuning capacitor was important. I ended up too low in frequency and
had to trim back a few Cu pipe sections.

3 skin depths gets you 95% of the conductivity. But the context isn't
making any sense. Copper tubing and solder joints. What are you
planning to plate to get 3 skin depths, the entire copper tube? I'm lost.

Yes, I want to silver plate the entire tube, any hardware that carries
RF, and possibly the tuning capacitor. The silver isn't what costs
money, it's the setup and plating labor. If all the copper parts are
plated individually, it's much easier, but then the solder doesn't get
plated. Plating the finished antenna is probably impractical. So, I
guess the solder doesn't get plated.

In my thinking you need to minimize the use of solder and keep it to as
small an area as possible. Because of the skin effect it will impact
any surface it is on the outside of. So get rid of it or don't use it
in the first place. Or use a very high silver content solder.

Agreed. However, I know what every home building will do. They'll go
to the hardware store, buy the plumbing parts, buy plumbers flux and
Sn-Cu solder, and solder it exactly like a plumber. Using silver
solder will probably be limited to the fanatics and those that have an
inventory of silver bearing solder.

Agreed. The only place where the solder might have an effect is on
mechanical rigidity. The small amounts used, even for a square loop
assembled from sections, it trivial compared to the losses in the
areas affected by skin effect. However trivial, it's not zero. I
suggest that you run the spreadsheet at:
http://www.aa5tb.com/aa5tb_loop_v1.22a.xls
and plug in various numbers for added resistance of the solder. The
numbers are tiny, but they will produce a noticeable change in Q and
therefore efficiency.

I think that is a pretty bogus statement. Using the default numbers in
the spreadsheet I could add up to 0.1 mohms before it even changed the Q
factor in the 4th significant digit. The formulas seem to be locked, so
I can't tell what is being done, but I assume the "added loss" is just
added to the loss resistance formula shown on the "formulas" sheet.

Tube thickness of 40 mils. Resistivity (rho) around 1.5 * 10^-7 ohm-m.
Tube diameter of 2 inches. Assume the solder forms a triangular fillet
in the L at the end of the overlap. Length of the hypotenuse is 56
mils. So change the triangle into a rectangle of half that length 28
mil and 28 mil high (max thickness from hypotenuse to right angle
corner). So the resistance will be...

I'm not sure this ascii art will help, lol.

Nice drawing. I like it.

---------,./.
| | \ .
| | \ . 56mil
40mil | \ .
| | \ .
| | \ .
---------' \ /
--------------------------
|-40mil-|

R = rho * L / ( W * H ) = 1.5e-7 ohm-m * 0.712 mm / (0.712 mm * 50.8
mm) = 3 micro-ohms. Yes, MICRO ohms.

Ok, I yield. That's a much smaller resistance than I would have
expected. Since the other resistive losses are 3 orders of magnitude
larger, I guess we can discount the resistance of the solder.

Unexplained issues are not really proof.

Agreed. I just thought my observations might be of interest. I think
I made it clear that I don't have a complete understanding of what
happened, only a guess(tm).

Someone in another group has a
coax antenna that detunes with temperature. I should ask him if it
detunes with time or just temperature. His frequency drift is some 20
times larger than I can explain with the expansion of the materials in
the capacitor and the loop. Since he is using the coax which is very
flexible, maybe the plastics involved are causing a dimensional change
large than would be seen for solid metal???

Good point. A few minutes with a heat gun should demonstrate the
cause of the drift. If he has an MFJ-259/269 antenna analyzer, it can
be used to measure resonance. White knuckle tuning is the only
problem:
https://www.youtube.com/watch?v=0CgO5ThFsQs (3:19)
I haven't tried this yet because I just bought a very used MFJ-269,
fixed it, and now the RF connector is intermittent. That's what I
should have been doing this weekend instead of ranting on usenet.

Solder may be softer than copper, but it is hard to explain how a solder
joint would change the length of the tubing by enough to cause a detune.

Good question. I don't have an answer. Something moved the tuning,
but I couldn't tell what it was. I might have soldered it together
under tension, which was somehow relieved by heating in transmit.
Dunno.

Sorry if my comments feel like pot shots. That is not my goal. I am
trying to understand what is being said. To be honest, a lot of your
comments seem to wander and not connect to what I have posted or even to
what you have stated elsewhere in the post or thread. This is probably
because I'm not picturing fully the ideas you have.

No problem, as long as you don't expect my unrelated experiences to
directly answer your question. I was working on a completely
different problem (minimum practical size of a loop) and not working
so much on the effects of soldering and plating. I apologize if my
experiences and speculation don't neatly dovetail with your questions
and seem unrelated. I had hoped that you would accept them as clues
or partial answer, not rigorous proofs.

To respond to your request, initially my interest was basically
academic, but as I hear more seat of the pants info from experienced
people I am more interested in finding out what really works and what
doesn't which means I'll have to build my own.

Once upon a time, I worked with an engineer who refused to build
anything until he completely understood the design. I was the exact
opposite, and would rush to build a prototype even if I had some
unanswered questions. The results were predictable. His final design
was usually good, took forever to deliver, and blew multiple
deadlines. Mine were a series of failures eventually leading to
something that worked. The total elapsed times were about the same. I
still don't know which method is better, but today I still prefer a
series of tweaked prototypes to a pile of calculations and a detailed
model. That might explain some of my recommendations and choice of
methods.

Did I ever send you my spice model? I haven't done anything with it in
a long time. It was a receiving antenna. One point I understand better
now is the radiation resistance which I could add in a calculation for.
Initially someone gave me a number I used. But for the small loop I
was looking at and the very low frequency (60 kHz) the radiation
resistance would be very tiny and so not really a factor.

You posted it to S.E.D. I looked it over but there were runtime
errors that I didn't want to fix. The title is Antenna_trans_loop.asc
dated 2013-02-27. If you have something later, I would be interested.
However, my abilities to use LTspice for RF design seems to have hit a
roadblock. About a month ago in S.E.D., I was involved in a
discussion about the operation of a common CATV splitter/combiner. I
decided to model the device with LTspice and ran into an odd problem.
The graphs produced by LTspice are in dB(volts) rather than dBm or
watts. I'm stuck trying to figure out how to produce dBm so that
graphs of filters, loops, and such look sane.

I want to build this from scratch if I do it. I don't see a problem
with aluminum.

No problem electrically. Big PITA mechanically because aluminum is
difficult to solder without Cu or Ag plating.

I can't see the benefit of soldering the rotor plates.

If you use an ordinary non-butterfly capacitor, the loop current goes
through the capacitor. That means it goes from the stator mounting
rod, through the plates, through the air, through the rotor plates,
though a bearing/bushing, and finally through the rotor shaft. Just
follow the RF path. Most of that path is fairly solidly built or
welded, but not the connections between the plates and the shafts.
Often, they're crimped together, resulting in a minimal point contact.
Better is on a threaded shaft, with compression making the connection.
Best is soldered, welded, or machined from a solid piece of metal.

A butterfly capacitor eliminates the worst culprit by removing the
rotating shaft from the RF path. There are two sets of stator plates
that need to be secured to two mounting shafts, but these are fairly
simple to build, compared to the rotor shaft found in the common
variable capacitor. The only problem is cost and the half the
capacitance from stator to stator.

So far no one has been able to explain how there would be any difference
in voltage except for very small values. If I felt the need to connect
them I would likely silver plate and solder rather than weld. But your
findings above with the lack of stability concern me with soldering, at
least in the main loop.

Well, the easy way would be to discount my observations and move
onward. The worst that can happen is that you'll repeat my
observations, my mistakes, or both.

As I previously concluded, the only real benefits of silver solder is
mechanical strength and rigidity. If your method of construction
requires these, such as if the tuning capacitor mounting is such that
movement of the loop will cause a movement in the capacitor, then
silver solder might help.

--
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 11/2/2015 12:17 PM, Jeff Liebermann wrote:
On Mon, 2 Nov 2015 00:16:42 -0500, rickman wrote:

Short replies... It's Monday and the phone is ringing.

There is a *big* difference between a precision machined connector and
concentric copper tubes. Heck, there is a big difference between
quality connectors and cheap ones!!! Besides, a coax connector isn't
designed to pass such high currents as a tuned loop antenna. Try
putting those in your loop and I bet it fails very quickly.

I'm using the shield connection, not the center conductor. The center
pin will probably be destroyed by the high currents and from arcing
due to high voltages. If crimped, the shield will probably survive.
If I wanted to prove it, I would calculate the square mils of surface
contact area for the shield in the connector. Overlapping CLEAN
copper 3/4" tubing makes a tolerable coax connector with the addition
of slots and a hose clamp for compression. I've seen Cu plumbing
parts used as welding cable connectors.

I don't know why you keep shifting gears. DC current is nothing like RF
current. DC will use every molecule of conduction path. The skin
effect hugely influences AC conduction making much of the connection
between two concentric conductors unavailable for conduction.

I looked up the coax connector shield connection and they are rated for
0.2 mohm outer contact and 0.1 mohm braid to body, so maybe they could
pass the large currents seen in these antenna. But that does not relate
to the concentric copper tube because the coax connector is specifically
designed for this. The copper tube is just the opposite.


When constructing a loop antenna of copper or aluminum tubing, what is
there to tweak that would be easier with unsoldered joints?

The lengths of various sections so that the tuning range of the
capacitor works as planned. My first plumbing loop was calculated for
a loop circumference based on the center line of the plumbing. I had
forgotten to include the length of the capacitor stator frame in the
loop length. I also found that the location where I attached my
tuning capacitor was important. I ended up too low in frequency and
had to trim back a few Cu pipe sections.

You have to do that exactly once. After that there is no reason to
leave the joints unsoldered.


3 skin depths gets you 95% of the conductivity. But the context isn't
making any sense. Copper tubing and solder joints. What are you
planning to plate to get 3 skin depths, the entire copper tube? I'm lost.

Yes, I want to silver plate the entire tube, any hardware that carries
RF, and possibly the tuning capacitor. The silver isn't what costs
money, it's the setup and plating labor. If all the copper parts are
plated individually, it's much easier, but then the solder doesn't get
plated. Plating the finished antenna is probably impractical. So, I
guess the solder doesn't get plated.

I don't see any useful value to silver plating. It gains you 2.5% in
improved conductivity. Really? You are the one telling me *I'm*
overdoing this. Also, I'm not planning to use copper, rather aluminum.
I found 20 foot lengths of aluminum 3 inch Al tubing for $3 a foot,
much cheaper and as good a conductor as 2.5 inch copper.

Why silver plate when you can get a bigger improvement by going up in
tube diameter?

The solder, properly done, will only cover a tiny fraction of the total
loop. Pointless to even consider plating it, especially when it can be
a silver compound as well.


In my thinking you need to minimize the use of solder and keep it to as
small an area as possible. Because of the skin effect it will impact
any surface it is on the outside of. So get rid of it or don't use it
in the first place. Or use a very high silver content solder.

Agreed. However, I know what every home building will do. They'll go
to the hardware store, buy the plumbing parts, buy plumbers flux and
Sn-Cu solder, and solder it exactly like a plumber. Using silver
solder will probably be limited to the fanatics and those that have an
inventory of silver bearing solder.

So? If people can't follow instructions they get what they get.


Agreed. The only place where the solder might have an effect is on
mechanical rigidity. The small amounts used, even for a square loop
assembled from sections, it trivial compared to the losses in the
areas affected by skin effect. However trivial, it's not zero. I
suggest that you run the spreadsheet at:
http://www.aa5tb.com/aa5tb_loop_v1.22a.xls
and plug in various numbers for added resistance of the solder. The
numbers are tiny, but they will produce a noticeable change in Q and
therefore efficiency.

I think that is a pretty bogus statement. Using the default numbers in
the spreadsheet I could add up to 0.1 mohms before it even changed the Q
factor in the 4th significant digit. The formulas seem to be locked, so
I can't tell what is being done, but I assume the "added loss" is just
added to the loss resistance formula shown on the "formulas" sheet.

Tube thickness of 40 mils. Resistivity (rho) around 1.5 * 10^-7 ohm-m.
Tube diameter of 2 inches. Assume the solder forms a triangular fillet
in the L at the end of the overlap. Length of the hypotenuse is 56
mils. So change the triangle into a rectangle of half that length 28
mil and 28 mil high (max thickness from hypotenuse to right angle
corner). So the resistance will be...

I'm not sure this ascii art will help, lol.

Nice drawing. I like it.

---------,./.
| | \ .
| | \ . 56mil
40mil | \ .
| | \ .
| | \ .
---------' \ /
--------------------------
|-40mil-|

R = rho * L / ( W * H ) = 1.5e-7 ohm-m * 0.712 mm / (0.712 mm * 50.8
mm) = 3 micro-ohms. Yes, MICRO ohms.

Ok, I yield. That's a much smaller resistance than I would have
expected. Since the other resistive losses are 3 orders of magnitude
larger, I guess we can discount the resistance of the solder.

Unexplained issues are not really proof.

Agreed. I just thought my observations might be of interest. I think
I made it clear that I don't have a complete understanding of what
happened, only a guess(tm).

Someone in another group has a
coax antenna that detunes with temperature. I should ask him if it
detunes with time or just temperature. His frequency drift is some 20
times larger than I can explain with the expansion of the materials in
the capacitor and the loop. Since he is using the coax which is very
flexible, maybe the plastics involved are causing a dimensional change
large than would be seen for solid metal???

Good point. A few minutes with a heat gun should demonstrate the
cause of the drift. If he has an MFJ-259/269 antenna analyzer, it can
be used to measure resonance. White knuckle tuning is the only
problem:
https://www.youtube.com/watch?v=0CgO5ThFsQs (3:19)
I haven't tried this yet because I just bought a very used MFJ-269,
fixed it, and now the RF connector is intermittent. That's what I
should have been doing this weekend instead of ranting on usenet.

Solder may be softer than copper, but it is hard to explain how a solder
joint would change the length of the tubing by enough to cause a detune.

Good question. I don't have an answer. Something moved the tuning,
but I couldn't tell what it was. I might have soldered it together
under tension, which was somehow relieved by heating in transmit.
Dunno.

What about other effects. What happens to the inductance if the loop is
a bit out of plane? Any idea if your loop flexes around in wind or
whatever?


Sorry if my comments feel like pot shots. That is not my goal. I am
trying to understand what is being said. To be honest, a lot of your
comments seem to wander and not connect to what I have posted or even to
what you have stated elsewhere in the post or thread. This is probably
because I'm not picturing fully the ideas you have.

No problem, as long as you don't expect my unrelated experiences to
directly answer your question. I was working on a completely
different problem (minimum practical size of a loop) and not working
so much on the effects of soldering and plating. I apologize if my
experiences and speculation don't neatly dovetail with your questions
and seem unrelated. I had hoped that you would accept them as clues
or partial answer, not rigorous proofs.

As to the minimum size of the antenna... the formula that surprised me
and made me realize there is a nearly brick wall is for radiation
resistance. It's proportional to the 4th power of the ratio of loop
radius to wavelength... the *4th* power! That is hard to overcome by
any small effect or even moderately large ones. Push just a little bit
and you see huge results, like making your loop 33% larger increasing
the radiation resistance by 3x! (or making your loop 25% smaller
reducing the radiation resistance 3x Makes it hard to get anything
like acceptable efficiency if the loop is even a little too small.


To respond to your request, initially my interest was basically
academic, but as I hear more seat of the pants info from experienced
people I am more interested in finding out what really works and what
doesn't which means I'll have to build my own.

Once upon a time, I worked with an engineer who refused to build
anything until he completely understood the design. I was the exact
opposite, and would rush to build a prototype even if I had some
unanswered questions. The results were predictable. His final design
was usually good, took forever to deliver, and blew multiple
deadlines. Mine were a series of failures eventually leading to
something that worked. The total elapsed times were about the same. I
still don't know which method is better, but today I still prefer a
series of tweaked prototypes to a pile of calculations and a detailed
model. That might explain some of my recommendations and choice of
methods.

Did I ever send you my spice model? I haven't done anything with it in
a long time. It was a receiving antenna. One point I understand better
now is the radiation resistance which I could add in a calculation for.
Initially someone gave me a number I used. But for the small loop I
was looking at and the very low frequency (60 kHz) the radiation
resistance would be very tiny and so not really a factor.

You posted it to S.E.D. I looked it over but there were runtime
errors that I didn't want to fix. The title is Antenna_trans_loop.asc
dated 2013-02-27. If you have something later, I would be interested.
However, my abilities to use LTspice for RF design seems to have hit a
roadblock. About a month ago in S.E.D., I was involved in a
discussion about the operation of a common CATV splitter/combiner. I
decided to model the device with LTspice and ran into an odd problem.
The graphs produced by LTspice are in dB(volts) rather than dBm or
watts. I'm stuck trying to figure out how to produce dBm so that
graphs of filters, loops, and such look sane.

Are you saying the version I posted didn't even run? Odd. It is late
now, but I'll try to dig it out tomorrow.


I want to build this from scratch if I do it. I don't see a problem
with aluminum.

No problem electrically. Big PITA mechanically because aluminum is
difficult to solder without Cu or Ag plating.

That's why I want to silver plate it. The plating looks to be easy.
Others have talked about being able to solder aluminum by using
something to block the air, but I don't recall the details. It sounds
much more difficult.


I can't see the benefit of soldering the rotor plates.

If you use an ordinary non-butterfly capacitor, the loop current goes
through the capacitor. That means it goes from the stator mounting
rod, through the plates, through the air, through the rotor plates,
though a bearing/bushing, and finally through the rotor shaft. Just
follow the RF path. Most of that path is fairly solidly built or
welded, but not the connections between the plates and the shafts.
Often, they're crimped together, resulting in a minimal point contact.
Better is on a threaded shaft, with compression making the connection.
Best is soldered, welded, or machined from a solid piece of metal.

But you still have the bearing contact which makes it impractical for a
transmitter from what I hear. No point in welding a rotor if you have
such a joint carrying the RF.


A butterfly capacitor eliminates the worst culprit by removing the
rotating shaft from the RF path. There are two sets of stator plates
that need to be secured to two mounting shafts, but these are fairly
simple to build, compared to the rotor shaft found in the common
variable capacitor. The only problem is cost and the half the
capacitance from stator to stator.

Not really an issue if the difference is that it works and the brushed
or bushed rotor doesn't work at high RF power levels.


So far no one has been able to explain how there would be any difference
in voltage except for very small values. If I felt the need to connect
them I would likely silver plate and solder rather than weld. But your
findings above with the lack of stability concern me with soldering, at
least in the main loop.

Well, the easy way would be to discount my observations and move
onward. The worst that can happen is that you'll repeat my
observations, my mistakes, or both.

Yes, but this will be a *lot* of work to assemble a large antenna like
this. The cost won't be small either.


As I previously concluded, the only real benefits of silver solder is
mechanical strength and rigidity. If your method of construction
requires these, such as if the tuning capacitor mounting is such that
movement of the loop will cause a movement in the capacitor, then
silver solder might help.

Yeah. I should stick by my guns and believe that standard tin-lead
solder just won't impact the function of the loop to any detectable level.

--

Rick

On Tue, 3 Nov 2015 03:37:36 -0500, rickman wrote:

Sorry, but I need to bail out of this interesting discussion for about
a week. I just landed another satellite dish repair job and need to
steal some time.

You have to do that exactly once. After that there is no reason to
leave the joints unsoldered.

I'm not suggesting that one build a loop that is NOT soldered.
However, I am suggesting that TESTING a loop that is not soldered is a
good idea in order to nail the tuning range.

Why silver plate when you can get a bigger improvement by going up in
tube diameter?

Because eventually, one runs out of diameter and has to use other
tricks in order to improve efficiency.

So? If people can't follow instructions they get what they get.

I'm one of those people. I find it embarassing to be caught reading
the instructions. Customers will think I don't know what I'm doing if
they see me reading the instructions. Besides, if the product were
designed correctly, it wouldn't need any instructions.

What about other effects. What happens to the inductance if the loop is
a bit out of plane? Any idea if your loop flexes around in wind or
whatever?

If I can find some mythical spare time, I'll buy an 8ft vent hose,
attach it to my LRC meter, and see what thrashing it around does to
the inductance. That should be a fair indication of what the tuning
might do. For fun, I might just tie it in a knot. Remind me in case
I get distracted by paying work.

As to the minimum size of the antenna.

My interest in the minimum size was inspired by an article that I
can't seem to find right now. The author claimed that scaling a loop
increasing the gain and efficiency, but the SNR (ratio between the
baseline atmospheric noise level picked up by the loop, and the
receive signal level) remains constant until the loop becomes so small
that the noise level drops below the thermal noise floor. I agree
with this but want to test it for myself. That means building a
collection of receive only loops with different L/C ratios. Hopefully,
I can derive or deduce some method for calculating the minimum usable
loop size.

.. the formula that surprised me
and made me realize there is a nearly brick wall is for radiation
resistance. It's proportional to the 4th power of the ratio of loop
radius to wavelength... the *4th* power! That is hard to overcome by
any small effect or even moderately large ones. Push just a little bit
and you see huge results, like making your loop 33% larger increasing
the radiation resistance by 3x! (or making your loop 25% smaller
reducing the radiation resistance 3x Makes it hard to get anything
like acceptable efficiency if the loop is even a little too small.

Hmmm... if that's correct, it might be useful for my quest for the
worlds smallest practical HF loop.

You posted it to S.E.D. I looked it over but there were runtime
errors that I didn't want to fix. The title is Antenna_trans_loop.asc
dated 2013-02-27.

Are you saying the version I posted didn't even run? Odd. It is late
now, but I'll try to dig it out tomorrow.

It ran, but with errors. I don't have your email address so I'll just
dump it on my web pile probably tomorrow evening.

That's why I want to silver plate it. The plating looks to be easy.
Others have talked about being able to solder aluminum by using
something to block the air, but I don't recall the details. It sounds
much more difficult.

Alumiweld. It's actually quite easy if you have an acetylene torch or
MAPP gass burner. Propane works, but I found more is more better. You
buy coated aluminum rod and braze normally. It wasn't difficult but I
did manage to screw up a few joints before I got the hang of it.
http://www.alumiweld.com
https://www.forneyind.com/store/detail/682/oxy-acetylene_welding_brazing_rod/5018/easy-flo_aluminum_brazing_rod_18_x_18_-_12_lbs/
http://www.harborfreight.com/8-piece-low-temperature-aluminum-welding-rods-44810.html
https://www.youtube.com/watch?v=CJ42scaWFnw
https://www.youtube.com/watch?v=y-iw3BiR4IQ
Lots of other videos on aluminum brazing on YouTube.
I have no idea how it will work on thinwall sections.

This is cute:
https://www.youtube.com/watch?v=TaSORWC-BMU
They're brazing an aluminum engine block by pre-heating the block in a
Weber barbeque.

--
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 11/4/2015 12:41 AM, Jeff Liebermann wrote:
On Tue, 3 Nov 2015 03:37:36 -0500, rickman wrote:

Sorry, but I need to bail out of this interesting discussion for about
a week. I just landed another satellite dish repair job and need to
steal some time.

Yeah, me too.


You have to do that exactly once. After that there is no reason to
leave the joints unsoldered.

I'm not suggesting that one build a loop that is NOT soldered.
However, I am suggesting that TESTING a loop that is not soldered is a
good idea in order to nail the tuning range.

Why silver plate when you can get a bigger improvement by going up in
tube diameter?

Because eventually, one runs out of diameter and has to use other
tricks in order to improve efficiency.

It is not very useful to get a 2.5% improvement. That's the bottom line.


So? If people can't follow instructions they get what they get.

I'm one of those people. I find it embarassing to be caught reading
the instructions. Customers will think I don't know what I'm doing if
they see me reading the instructions. Besides, if the product were
designed correctly, it wouldn't need any instructions.

What about other effects. What happens to the inductance if the loop is
a bit out of plane? Any idea if your loop flexes around in wind or
whatever?

If I can find some mythical spare time, I'll buy an 8ft vent hose,
attach it to my LRC meter, and see what thrashing it around does to
the inductance. That should be a fair indication of what the tuning
might do. For fun, I might just tie it in a knot. Remind me in case
I get distracted by paying work.

As to the minimum size of the antenna.

My interest in the minimum size was inspired by an article that I
can't seem to find right now. The author claimed that scaling a loop
increasing the gain and efficiency, but the SNR (ratio between the
baseline atmospheric noise level picked up by the loop, and the
receive signal level) remains constant until the loop becomes so small
that the noise level drops below the thermal noise floor. I agree
with this but want to test it for myself. That means building a
collection of receive only loops with different L/C ratios. Hopefully,
I can derive or deduce some method for calculating the minimum usable
loop size.

You are now analyzing receiving antennas. That's a gear shift. I've
been discussing transmitting antennas. Big distinction.


.. the formula that surprised me
and made me realize there is a nearly brick wall is for radiation
resistance. It's proportional to the 4th power of the ratio of loop
radius to wavelength... the *4th* power! That is hard to overcome by
any small effect or even moderately large ones. Push just a little bit
and you see huge results, like making your loop 33% larger increasing
the radiation resistance by 3x! (or making your loop 25% smaller
reducing the radiation resistance 3x Makes it hard to get anything
like acceptable efficiency if the loop is even a little too small.

Hmmm... if that's correct, it might be useful for my quest for the
worlds smallest practical HF loop.

Xmit and receive put very different requirements on the antenna. Which
do you wish to optimize? What power level/range are you shooting for?


You posted it to S.E.D. I looked it over but there were runtime
errors that I didn't want to fix. The title is Antenna_trans_loop.asc
dated 2013-02-27.

Are you saying the version I posted didn't even run? Odd. It is late
now, but I'll try to dig it out tomorrow.

It ran, but with errors. I don't have your email address so I'll just
dump it on my web pile probably tomorrow evening.

I seem to recall some errors were reported, but I don't recall them
being of any consequence.


That's why I want to silver plate it. The plating looks to be easy.
Others have talked about being able to solder aluminum by using
something to block the air, but I don't recall the details. It sounds
much more difficult.

Alumiweld. It's actually quite easy if you have an acetylene torch or
MAPP gass burner. Propane works, but I found more is more better. You
buy coated aluminum rod and braze normally. It wasn't difficult but I
did manage to screw up a few joints before I got the hang of it.
http://www.alumiweld.com
https://www.forneyind.com/store/detail/682/oxy-acetylene_welding_brazing_rod/5018/easy-flo_aluminum_brazing_rod_18_x_18_-_12_lbs/
http://www.harborfreight.com/8-piece-low-temperature-aluminum-welding-rods-44810.html
https://www.youtube.com/watch?v=CJ42scaWFnw
https://www.youtube.com/watch?v=y-iw3BiR4IQ
Lots of other videos on aluminum brazing on YouTube.
I have no idea how it will work on thinwall sections.

That's a big deal. It needs to work with thin tubing.

I'm happy with the idea of soldering.


This is cute:
https://www.youtube.com/watch?v=TaSORWC-BMU
They're brazing an aluminum engine block by pre-heating the block in a
Weber barbeque.



--

Rick

On Wed, 4 Nov 2015 01:27:16 -0500, rickman wrote:

On 11/4/2015 12:41 AM, Jeff Liebermann wrote:
On Tue, 3 Nov 2015 03:37:36 -0500, rickman wrote:

Sorry, but I need to bail out of this interesting discussion for about
a week. I just landed another satellite dish repair job and need to
steal some time.

Yeah, me too.

I'm back. I got a one week delay. I get to do the dishes next Thurs.
However, I still need to reduce my usenet time in order to get a few
important things done. (If I did everything I promised to do, I'd
never get anything done).

It is not very useful to get a 2.5% improvement. That's the bottom line.

Yes, but silver plating looks cool and will probably sell a few more
overpriced antennas. I guess the generic version should be polished
copper coated with Krylon, while the "pro" version might be silver
plated and coated with Krylon. Sorry, but no "Monster Cable" model in
2% gold is planned. Besides, at the high end, diminishing returns
becomes a fact-o-life. For a 2.5% improvement, you get to pay 50%
more. Seems fair to me.

You are now analyzing receiving antennas. That's a gear shift. I've
been discussing transmitting antennas. Big distinction.

Receive is my main area of interest. I'm trying not to do anything
that will preclude its use as a transmit antenna. At QRP levels
(5watts), the distinction isn't that big. The fun starts at 50 watts
and up. From the standpoint of construction, the big difference is
that the tuning cap has to handle high voltages and that the loop
needs to survive high currents.

Incidentally, this is one reason why I can't directly answer some of
your questions and why I seem to be drifting in topic. I'm following
my own reading and tinkering, not yours.

Hmmm... if that's correct, it might be useful for my quest for the
worlds smallest practical HF loop.

Xmit and receive put very different requirements on the antenna. Which
do you wish to optimize?

Initially, just receive performance. Once that's working and
understood, the tuning cap and loop construction can be beefed up to
handle the voltages and current levels needed for transmit.

What power level/range are you shooting for?

Initially QRP (5 watts). Next about 50 watts (digital modes).
Eventually, 150 watts (SSB). These can be 3 different models, with 3
different capacitors and 3 different mechanical designs. After some
tinkering, I know what it takes to make something that works in
transmit. What I don't know is how small I can make the loop and
that's what I'm initially working on calculating and testing.

An all too common problem is that the tuning changes between trnansmit
and receive. If I can't cure that, I'll probably need remote antenna
tuning, motor drive, uP control, etc.

I seem to recall some errors were reported, but I don't recall them
being of any consequence.

You haven't indicated if it's your model. I uploaded it to:
http://802.11junk.com/jeffl/antennas/magnetic-loop/Antenna_trans_LTspice/Antenna_trans_loop.asc
Is this the latest? This is what it produces:
Circuit: *
C:\blah-blah\jeffl\antennas\magnetic-loop\Antenna_trans_LTspice\Antenna_trans_loop.asc
Number of points per octave reduced from 3000000 to 19545.
Multiply defined .measure result: max
Each .measure statement needs a unique result name.
Date: Wed Nov 04 16:49:57 2015
Total elapsed time: 0.266 seconds.

I have no idea how it will work on thinwall sections.

That's a big deal. It needs to work with thin tubing.

Time permitting, I'll try it on whatever aluminum tubing I can find. I
have an aluminum ladder than could use some reinforcing, so I'll get
some practice. I'll probably have to use propane as oxy-acetylene
will probably burn a hole in it.

I'm happy with the idea of soldering.

"How to Solder Aluminum Thin Wall Tubing"
http://www.ehow.com/how_6069853_solder-aluminum-thin-wall-tubing.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