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