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HF VCO design

Posted: Wed Jan 08, 2020 9:47 am
by SamTheDog
Anyone here used a ring of inverters as a VCO on the HF bands.... I have tried it but it's a little too un-stable.

My current HF design uses the MC145163 as the PLL.... with a C-Mos VCO. (1-15MHz)


Re: HF VCO design

Posted: Sat Jan 11, 2020 2:07 am
by Albert H
The problem with the "ring of inverters" is all the harmonic crap you get from them all switching away, chasing their tails! I gave up trying to use that type of circuit.

I use a Colpitts VCO, using a BF244 for the oscillator (most other FETs will work), followed by a two-transistor buffer stage. The buffer output provides a few volts p-p to drive the next RF stages, and a nice 5V signal to feed to the PLL. On shortwave, I use one of two PLL circuits - either the discrete 74HC CMOS IC-based type (4060 reference, 4046, 4040 pre-set divider). For quick, cheap rigs, I've used the squarewave VCO in the 4046 as the oscillator, but I prefer the FET and transistor approach to give a nice, monotonic signal. If you want the circuits, drop me a PM!