HF VCO design

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SamTheDog
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HF VCO design

Post by SamTheDog » Wed Jan 08, 2020 9:47 am

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)

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Sam The Dog.....

TOR-Radio on FM / Mediumwave and Shortwave
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Albert H
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Re: HF VCO design

Post by Albert H » Sat Jan 11, 2020 2:07 am

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!
"Why is my rig humming?"
"Because it doesn't know the words!"
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