Very good presentation, indeed, Dennis! Thanks.
With respect to the Clapp oscillator. Please refer to the drawing attached. It is a very simple design but appears to be working very good. I also made a design by prof Jeremy Everard of the York University (please google) with low noise lf transistors, but it looks like the Clapp shows less noise. With the same cheap crystals.?
My Phase Noise Test Set is basically analog by design (by DG4RBF, UKW Berichte 4/2015), I am an analog guy, and the sound card will process the spectrum (very well) by a sw called Audiometer (by DG8SAQ). It is pretty standard in that it consists of a diode ring mixer as phase detector followed by a ultra low noise Wenzel based lf amplifier (60 dB). There is also a PLL to keep the oscillators at quadrature. The amplifier is sensitive enough to show the thermal noise of a 50 ohm resistor. Obviously, you need two oscillators so one of them is provided with EFC. As reference I use a HP10811 at 10 MHz, a Clapp at 14 MHz and at 100 MHz an overtone oscillator with a fet. I hope to order good quality 14 and 100 MHz crystals to see if it makes any difference. The 14 and 100 MHz oscillators are followed by a low pass filter and if necessary an attenuator to get about +6 dBm output power. This is what my PNTS prefers. Moving the DUT power up and down 3 dB moves the spectrum up and down about 1 dB. The convergence of the spectra at the high end (previous post) seem an anomaly of the sound card used. In any case I consider an accuracy of 1 dB in this set up as good (enough).?
So far some more details. Feel free to ask for more info.
Best regards,
Harke
