parametric detector

In message , colin writes

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

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Hi, thanks, yes thats right :)

well it is actualy a modulation signal im trying to detect rather than just noise but it is very similar problem, of course the phase noise of the reference oscillator is a big issue but I intend to try and null most of that out I hope.

I'l go looking for some nice shiny quartz rocks... I chose 4mhz as it seemed they had the lowest series resistance for the frequency coresponding to highest Q although manafacturers dont list Q on a per frequency basis, its generally 20k for off the shelf types, im not sure if its advantagous to use an overtone or not. Im not sure if i can get any better ones, but the ones i bought seem to demonstrate a higher Q than anticipated from the simulation.

aha, I have looked at using it in parrellel mode trying to use the considerably high voltage generated from resonance to improve snr before detection, although I was woried about destroying the crystal I can easily see 50v pk-pk. I will experiment with the series mode in ltspice, the problem with most

so could a 400mhz cavity have a higher Q ?

Ive seen test aplication where the same type of oscillator is used as the reference if it is a VCXO of course. Ive tried using a PLL with a OCXO but this proved disapointing, of course one never fuly knows if its the topology used or just unlucky construction with such low snr, from what I can gather I think 1/f noise can be degraded with handling/soldering etc.

Thats quite impressive.

I will look into this with interest.

thnks

Colin =^.^=

In message , colin writes

Intrinsic acoustic loss is per cycle so ltimate q reduces from about

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Hi again,

I looked at using series resoance with a 50ohm resistor but the much lower voltage means a much smaler signal even tho the slope is higher, I did consider a curent transformer aproach but think it wpould be pushing things a bit to actualy get more SNR.

I looked at auto zero amplifiers and found they auto cancel the 1/f noise along with the dc offest, the AD8552 looks superb, very low voltage noise

I couldnt find much on error multipliers, maybe il look some more ...

Colin =^.^=

In message , colin writes

I looked and did not find, the technique was to multiply a 1MHz test signal to 10MHz mix with 9 MHz clean reference filter the resultant 1MHz and multiply again to 10MHz mix with the reference again can be done 4