Harmonic VXO
Greetings:
I needed a quick,
very temperature + frequency stable oscillator @ 50.8 MHz to test a receive mixer. Already running elsewhere on my bench, my main VHF signal generator wasn't an option.
Without going to a digital signal box, I weighed my build options:
- VFO — difficult to stabilize at VHF.
- VCO — even more difficult to stabilize at VHF and it's too much work to make a PLL for it.
- Overtone crystal oscillator — little chance of finding a crystal to vibrate at 50.8 MHz.
- Fixed crystal oscillator — need a crystal to vibrate at exactly 50.8 MHz. Right!
- VXO — do I own a 10.16, 16.93 , 25.4 MHz etc. crystal ?
- VXCO — still need a crystal to double, or take a harmonic from. The varactor will add phase noise, but might work.
Then came a mad search. Soon enough, I found a long forgotten bag of crystals and after 10 minutes of fumbling with it, I felt jubilant to find a 16.9344 MHz crystal! Good, I'll make a VXO with an output filter to help suppress all but the 3rd harmonic.
I grabbed a copper board and began soldering — no need for a schematic, for I've made many tens of xtal oscillators in my sleep. About 20 minutes later, I was done and ready to measure the ugly thing.
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