Re: parametric detector

In message <Z6Qze.7334$Dq.3916@xxxxxxxxxxxxxxxxxxxx>, colin <no.spam.for.me@xxxxxxxxxxxx> writes 
Hi,
  Im looking at using a parametric method for a phase detector,
The source (~4mhz) is already very strong but the sideband, @ 1-10hz, is
extremely low, I am considering using a quartz crystal as the most sensitive
slope detector but to get a significant signal to noise ratio I would need a
crystal with a Q of over a million. I dont expect acheiving such a high Q is
practical, unless cooling it drasticaly would help ?

The main noise problem is 1/f noise especialy as a high Q circuit would need
a high impedance amplifier and a mosfet would have too high 1/f noise at
<10hz.

However I cant see a way of using a paramatric method for a detector, at
least not with any gain, I havnt realy looked at them much before, although
I know the basic principles of operation of using as using variable
reactance in a ac voltage dividor or charge/voltage pump.

I came accros an old parametric amplifier by AD the 310/311 but I doubt they
make this any more, at least something like this might be usefull after a
diode detector, although I am not sure about how much the diode noise
particularly 1/f noise would be.

Colin =^.^=


I understand that you intend to apply a 4MHz signal with low sidebands to a high Q crystal offset slightly so that pahse modulation will appear as amplitude modulation and then perhaps employ a low frequency speactrum analyser to look at the phase noise. Is this the idea?
If so:
A good quality 4MHZ crystal wcan have a Q approaching 1000000.
All depends on the diameter/contour surface polish and the quality of quartz used.
The crystal could be operated at its series resonance and terminated in 50 ohms so that a <1nVroot Hz amplifier could be used.
The technique is not unknown, Marconi manufactured a tuneable cavity in the 400MHz range for the purpose.
The orthadox approach would be to mix a high q crystal reference frequency with the "unknown" and explore the LF result with an analyser.
I did well with this approach employing the steep side of an ssb crystal filter to attenuate the resultant mixed carrier whilst looking at the 0 to 3kHz ssb noise.
With careful use of low noise gain blocks stepped attenuator to overcome the dynamic range limitations of the 141T I could see down to -145db from the carrier.
For another approach see error multipliers , these circuits are seldom seen now but you may be able to buy an old Tracor ? for the purpose.

Finally a counter with low noise reference, high clock frequency and multiperiod capability can be programmed to convert jitter to ssb noise.
See "AllensTime"

note demon email address invalid
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