VCO frequency noise is measured. V input is 4.7 Volt. The signal output from the VCO (which controls the AOM) is mixed with signal from ifr2023 at ~80MHz. The demodulated signal
is then fed to SR560. Gain setting is 5 x10^3, low pass at 1Hz. The output signal is split into two. One is sent back to ifr2023 for freq modulation, another one is fed to the spectrum analyzer. The voltage output is
then converted to frequency by calibration from last week (0.714 MHz/V).
The plot shows frequncy noise from:
1: function generator (ifr2023) in brown
2: VCO, in pink
3&4 Frank's RC noise data from FEB09, in red and blue
5: RCnoise from beat measurment, in green
6: estimated noise
VCO seems to limit our noise at f=100Hz and higher/
you have to measure a new calibration coeff. If you change the center frequency of the marconi the maximum FM modulation range changes too and so the coeff. If i remember right your range was 500kHz compared to 1Mhz last week, right? So it should change about a factor of 2 or so, so the actual measured noise is a little bit less but nevertheless much to high
Yes, I completely forgot about that. I calibrated it again, at 80Mhz, 7.0 dBm, freq devn 500khz. and it is 0.35655 MHz/volt. About a factor of 2 smaller.
I'll put up the corrected plot soon.