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

On 11/4/2015 8:06 PM, Jeff Liebermann wrote:
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.

I believe gold is not as good a conductor as copper. The rank is
silver, copper, gold, aluminum with silver only 5% better than copper
which is mitigated to 2.5% with the skin effect.

I'm looking at aluminum because of the cost and the weight, but
noticeably less with aluminum.


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.

Receive and transmit are opposed goals for optimization. A high
radiation resistance means some of your received signal is radiated
again. A low radiation resistance lowers the transmission efficiency.
The other issues both have in common, but it is easier to optimize a
receive antenna than a transmit antenna. I have seen more than one have
use separate antennas for each.


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.

It makes a huge difference. No one makes a transmit antenna with
multiturns and small wire which are both perfectly ok for receive. Here
are the key equations for receive antennas...

In general the receive voltage relates to the various parameters
assuming the radiation resistance is small -
L � r * ln(r) * N2
R � r * N
Q � N * ln(r)
V � r² * N * Q * ln(r)
V � r² * N² * ln(r)
l � r * N * ln(r)
V � l² * ln(r)

So maximizing signal strength means maximizing the total length of the
coil independent of the number of turns other than the small effect from
ln(r). Smaller loops with more turns is nearly as good as larger loops
with fewer turns. Not so for transmitting antennas because the
radiation resistance which needs to be than the ohmic resistance. A
large radiation resistance can hurt the Q relative to what you get with
a receive antenna.

Consider using two antennas where the receive antenna has a lot more
length. No high voltages or currents are used so the components can be
much less costly. A simple air cap with a standard wiper or bearing
connected rotor can be used.


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.

Are you talking about self heating effects?


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.

Yes, I wrote the simulation with help from a variety of sources. The
above is not really an error. Just reduce the number of points used. I
don't recall how that is set, but much of it is parametrized.

I'm not sure what is up with the MAX error report. That sounds like a
problem with a line continuation.


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 have a friend who is a great welder, but he is older than myself and
doesn't spend much time in the shop these days. I visited him today and
we just hung out in the workshop and talked about stuff. He is trying
to improve his TV reception by adding another antenna on the same pole
and connecting the two together through one preamp. I told him if the
antenna are close together they may interfere and using one preamp is
likely to be a problem. He was not happy...


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

I will look into that.

--

Rick

On Wed, 4 Nov 2015 21:24:55 -0500, rickman wrote:


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.

Yes, I wrote the simulation with help from a variety of sources. The
above is not really an error. Just reduce the number of points used. I
don't recall how that is set, but much of it is parametrized.

I'm not sure what is up with the MAX error report. That sounds like a
problem with a line continuation.

That was the .ac directive. Too many points per octave.

Here's my tweaked version of the loop. No errors this time:
http://802.11junk.com/jeffl/antennas/magnetic-loop/Antenna_trans_LTspice/Rickman_60KHz_loop_02.asc
Screen grab of the output:
http://802.11junk.com/jeffl/antennas/magnetic-loop/Antenna_trans_LTspice/Rickman_60KHz_loop_02.jpg

What I done did:
1. Removed all the .MEAS stuff that was producing errors. Just put
the probe on the "output" line.
2. L1 and L2 were over coupled. I reduced the coupling from 1 to
0.02. I intentionally did NOT overlap the resonant peaks so the
tuning is slightly off. It's fairly close to critically coupled.
3. Adjusted C1 and C2 for 60 KHz tuning.
4. Change frequency axis (.ac) parameters.
5. I got lazy and didn't add the usual title block stuff.
6. There are no values for Rs which needs to be considered.

I hope this helps and I'm gone for dinner.

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