Re: Ver. 1.42 and crystal measurement

Nick Kennedy
 

Hi Ted,

It seems you're aware that Ignacio added another set of polynomial
constants to parameters.txt in revision 1.42, so I can't blame that. Yes,
you may have read in the User's Guide about "cheating" on the parameters
just to get the system working. I don't remember the step by step process,
but if you just read the dBm value somewhere in mid-range and "pretend"
that it's the same everywhere can calculate constants from that, you'll get
constants that "work" but don't properly compensate for changes in the
generator and crystal test fixture with frequency. I assume the higher
coefficients will come out zero, but don't remember for sure. Probably the
constant value C0 will equal the dBm value you measured at mid-band and all
other coefficients will be zero.

Anyway though ... you are getting the message that PHSNA can't find a peak.
In a case like that I'd do "normal" response sweep around the crystal
frequency and look at the plot to verify that there IS a peak. Maybe use 10
Hz steps, at least initially. If there's not one, maybe you have a hardware
issue. If there is one, make sure its frequency is consistent with the
scanning range you are telling PHSNA to use when you go into the crystal
test mode.

Good luck & keep us posted.

Nick, WA5BDU

On Fri, May 15, 2020 at 7:22 PM Ted KX4OM <wirehead73@...> wrote:

Welcome to the new moderators!

I've been measuring a lot of crystals the past week, about a hundred in
all. About 50 in 8.192 HC49/U from a batch of 100 of which I had measured
previously, and about 50 8.386 HC49/US that Harold Smith, KE6TI gave me a
few years ago, about 100 in all. The latter have an average Q of around
200,000 while the 8.162 ones are about 100,000. The PHSNA makes it so easy,
much moreso than my homebrew K8IQY PVXO and G3UUR rigs.

Here is my problem: A year ago, I upgraded to Rev 1.42 and used it to
check my 40m dipole to set its length. That replaced my G5RV. Great, no
problem. I had also used it to sweep some Heathkit SSB and CW crystal
filters. That's all I used it for. I *think* I did the new crystal
measurement frequency polynomial coefficients correctly when I installed
1.42; the ones in parameters.txt aren't Nick's from the 1.42 files. Last
week when I started to measure the crystals, it would search for a long
time and then would send an error message "Unable to find peak RF
frequency" or something like that. I reinspected the parameters.txt file
and everything looked okay. I ended up saving 1.42 to a bak directory and
replaced it with 1.40, the last version I had used to do crystals back in
2018. What is odd is that I could do a response sweep in 1.42 on a crystal
and get the peak frequency, but I couldn't sweep a jumpered holder in the
standard PHSNA crystal test board (not using the amplifer, and always using
an additional 4 dB attenuator from the SNA.

From reading the docs, I think I understand that I could put in some value
for the five coefficients in 1.42 that aren't real, and that would allow
the crystal measure to function as if it was a later version. Any ideas?

Ted, KX4OM



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