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Technical Topics => The RF Workbench => Topic started by: ThaDood on May 10, 2024, 1757 UTC

Title: Low-cost RF synthesizer uses generic ICs?
Post by: ThaDood on May 10, 2024, 1757 UTC

https://www.edn.com/low-cost-rf-synthesizer-uses-generic-ics/  Boomer and I were talking about what could you use a crystal, that was common in 1980's digital watches, for. Well, this was his answer. Neat!!!!

Title: Re: Low-cost RF synthesizer uses generic ICs?
Post by: Stretchyman on May 20, 2024, 0719 UTC

DDS if a far simpler solution as its a single chip.

AD9833 is available with clock on a pcb for <$2.

Just add lpf and attiny45 to talk to it and you've got dc-12MHz.

Title: Re: Low-cost RF synthesizer uses generic ICs?
Post by: Kage on May 23, 2024, 1525 UTC

One idea I had when building the old tried and true 3 IC MW PLL using the 4046 was its potential use to cover up into HF by using the modern TI versions that are good for up to around 14MHz and adding a second 40103 for further DIP switch division.
If using the circuit to drive push-pull it should be good to 7MHz but this is just a theory in my head, and honestly setting that many DIP switches
to get on frequency would be a pain and really only useful for 10kHz spacing unless using single ended in which case I suppose it's possible to use
5kHz spacing.
All that should be required is tying the 8-bit binary counter 40103 to another to get to 16-bit, and using the latest 74xx.. series ICs that support those higher frequencies since the original 4046 was really only good up to a few MHz as I recall.

Either way that old 3 chip solution for making a mediumwave synthesizer still runs rock solid in a few designs I've made over the years and it doesn't get much simpler for using classic ICs. Shouldn't be too hard to scale up to the HF band if one is willing to experiment. You'll only get 5v logic outputs from the latest though so either the designer has to use a gate driver IC or one of the more special mosfets that can be directly driven at that level which most will crap out at driving higher frequencies from gate capacitance. It's usually recommended to use a gate driver IC anyway though in these sort of designs.

Title: Re: Low-cost RF synthesizer uses generic ICs?
Post by: redhat on May 24, 2024, 0131 UTC

This is faster and not limited to the step size of your divider.  I've used these to driver commercial transmitters, am stereo exciters, as well as my own rigs.

https://www.ebay.com/itm/186071392182 (https://www.ebay.com/itm/186071392182)

+-RH