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

On 11/4/2015 10:31 PM, Jeff Liebermann wrote:
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.

Why is this over coupled?


3. Adjusted C1 and C2 for 60 KHz tuning.
4. Change frequency axis (.ac) parameters.

I like to have a major tick at the frequency I am interested in, 60 kHz
in this case.


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.

What is Rs, the loss resistance? Hmmm, this must have been an older
copy, I am sure I included that, possibly in one of the coils since that
is what it is from. I'm not sure I included radiation resistance as I
barely knew what that was. I recall someone said it should be in there
and gave me a rough value which was very small. I now understand it
better and the calculated number is 2.669E-010 ohms, so obviously it can
be totally ignored.

My real circuit had some other components at the output that complicate
the real circuit. The "receiver" is an FPGA with a very high input
impedance. To bias the input to the threshold of the input there is an
output of the quantized value which is filtered by an RC circuit and
used to bias the other side of the CT secondary rather than grounding
it. I haven't decided on the exact circuit for the digital side.

--

Rick

On Wed, 4 Nov 2015 23:50:38 -0500, rickman wrote:

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.

Why is this over coupled?

When you couple together two tuned circuits, over coupling will result
in an overly broad peak (low Q) while under coupling will result in
low output. The degree of coupling also has some effect on whether
you see one or two peaks in case you really do want a broadband
design. For a 60 KHz loop, you want it as narrow as possible, even if
it means some additional loss.

For a power xformer, you always want as much coupling as possible with
as little stray fields leaving the transformer. However, for tuned
circuits, you want whatever coupling gives you the desired bandwidth.
Different goals, I guess.

3. Adjusted C1 and C2 for 60 KHz tuning.
4. Change frequency axis (.ac) parameters.

I like to have a major tick at the frequency I am interested in, 60 kHz
in this case.

So, add it. I spent about 15 minutes (mostly tuning L1 and L2) making
the changes and left out all kinds of goodies that would be nice.
Title block info, formatting L3/L4 to look like an xformer, etc. I
also didn't do a sanity check on any of the components. However, in
this case I can't help. I don't know how to add a frequency marker
and couldn't find any clues with Google.

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.

What is Rs, the loss resistance?

Yes.

Hmmm, this must have been an older copy,

Yep, it appears to be missing some things.

I am sure I included that, possibly in one of the coils since that
is what it is from. I'm not sure I included radiation resistance as I
barely knew what that was. I recall someone said it should be in there
and gave me a rough value which was very small. I now understand it
better and the calculated number is 2.669E-010 ohms, so obviously it can
be totally ignored.

L2 has Rs=7 ohms. L3 has Rs=0.325 ohms. I think both are rather high
for a 60 KHz loop. The other coils have no value for Rs.

When I do an antenna, I usually have the design running in 4NEC2,
which provides me with various parameters including radiation
resistance, efficiency, etc. I don't know what a sane number would be
for a 60 KHz loop, but can probably find a WWVB antenna model that
would give a ballpark value. (However, not now).

My real circuit had some other components at the output that complicate
the real circuit. The "receiver" is an FPGA with a very high input
impedance. To bias the input to the threshold of the input there is an
output of the quantized value which is filtered by an RC circuit and
used to bias the other side of the CT secondary rather than grounding
it. I haven't decided on the exact circuit for the digital side.

High impedance means high voltages. If you use a realistic value for
the input voltage instead of 1, it will show if you're going to
overload your FPGA A/D converter or whatever you're using for input.



--
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 11/5/2015 12:35 AM, Jeff Liebermann wrote:
On Wed, 4 Nov 2015 23:50:38 -0500, rickman wrote:

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.

Why is this over coupled?

When you couple together two tuned circuits, over coupling will result
in an overly broad peak (low Q) while under coupling will result in
low output. The degree of coupling also has some effect on whether
you see one or two peaks in case you really do want a broadband
design. For a 60 KHz loop, you want it as narrow as possible, even if
it means some additional loss.

For a power xformer, you always want as much coupling as possible with
as little stray fields leaving the transformer. However, for tuned
circuits, you want whatever coupling gives you the desired bandwidth.
Different goals, I guess.

How do you control the coupling in the real circuit? I was planning to
use a current transformer which I assume would be strongly coupled. Of
course, I was minimizing C2 which resulted in a high frequency second
peak far above the 60 kHz peak. I don't recall seeing a poor Q in the
circuit. Q is useful to minimize any nearby interference, but otherwise
my concern is max signal strength to get enough signal to be detected by
the crude FPGA comparator input.


3. Adjusted C1 and C2 for 60 KHz tuning.
4. Change frequency axis (.ac) parameters.

I like to have a major tick at the frequency I am interested in, 60 kHz
in this case.

So, add it. I spent about 15 minutes (mostly tuning L1 and L2) making
the changes and left out all kinds of goodies that would be nice.
Title block info, formatting L3/L4 to look like an xformer, etc. I
also didn't do a sanity check on any of the components. However, in
this case I can't help. I don't know how to add a frequency marker
and couldn't find any clues with Google.

You have to add a cursor which reads out in a small window, (and may not
show up in screen captures, can't recall) or you can do a measurement...
which you removed.


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.

What is Rs, the loss resistance?

Yes.

Hmmm, this must have been an older copy,

Yep, it appears to be missing some things.

I am sure I included that, possibly in one of the coils since that
is what it is from. I'm not sure I included radiation resistance as I
barely knew what that was. I recall someone said it should be in there
and gave me a rough value which was very small. I now understand it
better and the calculated number is 2.669E-010 ohms, so obviously it can
be totally ignored.

L2 has Rs=7 ohms. L3 has Rs=0.325 ohms. I think both are rather high
for a 60 KHz loop. The other coils have no value for Rs.

Uh, high or not, that is the circuit I was simulating. 50 feet of RG-6
coax, solid copper inner conductor and a current transformer I don't
have a part number for off the top of my head. I was looking for the
turns ratio to give the optimum output voltage from the current
transformer giving the load circuit. I'm not sure the simulation would
provide that given the strong dependance on Q which can be affected by
many unplanned effects. I have already built a frame for 8 turns of
coax, but am thinking more would be better to increase the voltage and Q.

BTW, it is hard to get much lower on the resistance (skin depth = 0.266
mm) so the Q is about as high as you can get unless you use *much*
bigger wire or tubing or add lots more turns. Since adding turns boosts
the signal strength I think that is better than the more exotic types of
conductors that are required for transmitting loops.

Remember, the absolute resistance isn't important, it's the ratio of
inductive impedance to resistance.


When I do an antenna, I usually have the design running in 4NEC2,
which provides me with various parameters including radiation
resistance, efficiency, etc. I don't know what a sane number would be
for a 60 KHz loop, but can probably find a WWVB antenna model that
would give a ballpark value. (However, not now).

Most WWVB antennas are ferrite loops. Good luck.


My real circuit had some other components at the output that complicate
the real circuit. The "receiver" is an FPGA with a very high input
impedance. To bias the input to the threshold of the input there is an
output of the quantized value which is filtered by an RC circuit and
used to bias the other side of the CT secondary rather than grounding
it. I haven't decided on the exact circuit for the digital side.

High impedance means high voltages. If you use a realistic value for
the input voltage instead of 1, it will show if you're going to
overload your FPGA A/D converter or whatever you're using for input.

Uh, I seriously doubt I can overload the input with just an antenna no
matter how well it is constructed. Look at the E field for the WWVB
transmitter and you will see it is very marginal receiving it at all on
the east coast.

I just want to fix a couple of typos in the formulas I posted earlier
for my own benefit. These help me see what is going on.

L � r * ln(r) * N²
R � r * N
Q � N * ln(r)
V � r² * N * Q * ln(r)
V � r² * N² * ln(r)
V � (r * N)² * ln(r)
l � r * N
V � l² * ln(r)

V = voltage
l = wire total length
L = inductance
R = resistance
r = radius of loop
N = number of turns
Q = quality factor

--

Rick

On Thu, 5 Nov 2015 02:44:24 -0500, rickman wrote:

How do you control the coupling in the real circuit? I was planning to
use a current transformer which I assume would be strongly coupled. Of
course, I was minimizing C2 which resulted in a high frequency second
peak far above the 60 kHz peak. I don't recall seeing a poor Q in the
circuit. Q is useful to minimize any nearby interference, but otherwise
my concern is max signal strength to get enough signal to be detected by
the crude FPGA comparator input.

The Q is approximately set by the ratio of:
tuning_capacitor / coupling_capacitor
However, that doesn't work with inductive coupling where the Q is
controlled by the inductors individual Q. I guess Q is the wrong
term. When you critically couple a collection of LC circuits, as in a
multi-section bandpass filter, the curve goes directly through the 3dB
bandwidth points, no matter how many stages are coupled. In other
words, the Q is set by the Q of one section.
What does change is the filter shape factor, which is the ratio of:
30_dB_bandwidth / 3_dB_bandwidth
or ocassionally:
6_dB_bandwidth / 6_db_bandwidth
depending on which reference book you're following. The first is more
common. Adding additional criticially coupled filter stages doesn't
change the Q, but really changes the shape factor. I can fire up a
filter design program to illustrate how it works, but not now.

I'm also a bit worried about the way you're feeding your FPGA directly
from mag loop. The problem is that WWVB uses both an amplitude
modulated time code, as well as the new phase modulated time code.
Decoding the former is going to require some AGC (automatic gain
control) to insure that the FPGA A/D converter is not going to get
clipped, go non-linear, or offer too low a signal level to get a
decent SNR. The phase modulated signal doesn't have this problem, but
has patent issues if you're going to try an sell chips or devices.
https://en.wikipedia.org/wiki/WWVB#Phase_modulation

Gone for a hot chocolate break...
--
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 11/5/2015 8:27 PM, Jeff Liebermann wrote:
On Thu, 5 Nov 2015 02:44:24 -0500, rickman wrote:

How do you control the coupling in the real circuit? I was planning to
use a current transformer which I assume would be strongly coupled. Of
course, I was minimizing C2 which resulted in a high frequency second
peak far above the 60 kHz peak. I don't recall seeing a poor Q in the
circuit. Q is useful to minimize any nearby interference, but otherwise
my concern is max signal strength to get enough signal to be detected by
the crude FPGA comparator input.

The Q is approximately set by the ratio of:
tuning_capacitor / coupling_capacitor

Not sure where you get this. Q is a measure of the energy stored
compared to the energy lost. If the coupling capacitor were the only
path of lost energy that might work, but I've yet seen a situation where
that is the case.


However, that doesn't work with inductive coupling where the Q is
controlled by the inductors individual Q. I guess Q is the wrong
term. When you critically couple a collection of LC circuits, as in a
multi-section bandpass filter, the curve goes directly through the 3dB
bandwidth points, no matter how many stages are coupled. In other
words, the Q is set by the Q of one section.
What does change is the filter shape factor, which is the ratio of:
30_dB_bandwidth / 3_dB_bandwidth
or ocassionally:
6_dB_bandwidth / 6_db_bandwidth
????
depending on which reference book you're following. The first is more
common. Adding additional criticially coupled filter stages doesn't
change the Q, but really changes the shape factor. I can fire up a
filter design program to illustrate how it works, but not now.

You are assuming the two filters are coupled in a useful way. If the
frequency of the parasitic filter is far above 60 kHz it can be ignored
other than the possibility that it picks up a radio station which
clobbers the WWVB signal.


I'm also a bit worried about the way you're feeding your FPGA directly
from mag loop. The problem is that WWVB uses both an amplitude
modulated time code, as well as the new phase modulated time code.
Decoding the former is going to require some AGC (automatic gain
control) to insure that the FPGA A/D converter is not going to get
clipped, go non-linear, or offer too low a signal level to get a
decent SNR. The phase modulated signal doesn't have this problem, but
has patent issues if you're going to try an sell chips or devices.
https://en.wikipedia.org/wiki/WWVB#Phase_modulation

I didn't see anything about patents.

You worry far too much about "overloading" the FPGA input (single
comparator). My concern is being able to detect a signal at all.


Gone for a hot chocolate break...



--

Rick