vfo stabilizer

Lets say I was operating 24.0 to 24.25 Ghz ISM band, and the VCO had a built in divide by 16. Anyone have a neat way to determine if I am tuning outside of that band (drift/aging/temperature) using the divider output.

Can not find a cheap off the shelf saw resonator or bandpass filter at 1.5078125 Ghz. Can I make a printed resonator in FR4 that will be stable enough to make the measurement? Any other way? Can not afford to phase lock it, and would prefer to not divide down any further.

Thanks,
Rich

The name of the circuit that could help you is: “VFO stabilizer”.
This is not a PLL, is just a cheap idea, to stabilize the frequency of a variable frequency oscillator (invented by radio amateurs back in 70’s).
The signal from a stable on-board crystal oscillator and a sampling of the signal from the VFO are both processed through binary counters to develop a high degree of accuracy, and then integrated to generate a control voltage.This controlling voltage is applied back to VFO (VCO in your case). The control voltage is used in a way that is inverse to the direction of the drift, so drift is corrected as it happens.

This approach may not fit to your relative high frequency (1.5GHz) if you don’t use more dividers, but gives an idea how it works.

http://www.hanssummers.com/huffpuff.html
http://members.ziggo.nl/cmulder/ksbstabi.htm

Thanks. That is exactly the type of circuits I was hoping for. Let me wad thru the pdfs and try to figure a way to do it at 1.5 GHz.