OK Hans,
Tnx for advice. Nice dds design, but i will first try what is possible with the 4-ic huff and puff (2x 74hc4060, 74hc74+opamp). I do not want to make things too fancy for a starter. Maybe later.
Yesterday i inserted some polysterene cap's and glued (bizon kit!) ?the fixed value coil to the pcb. Stability really improved. A trial of one hour showed about 300 Hz drift. Adding the huff and puff circuitry should further improve the situation. Maybe soldering a box from unetched pcb material around the vfo helps too.
Good homebrewing and best wishes from Holland
Ron
PA2RF
Hans Summers wrote:
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Ron, Raj...
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I have a simple DDS design too, which doesn't need microprocessors: ?. It would be possible to replace the DIP switches with up/down counters, driven perhaps by an optical shaft encoder. Not an optical encoder you buy very expensively! There are two in every computer mouse, available usually as free scrap. Just a little work required to convert it into a shaft encoder.
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Personally though I am still nervous about the noise and spurious outputs from DDS generators. I'm Ok with using it in a transmitter but I'd worry about using it in a receiver and degrading performance. Perhaps I'm just paranoid. Mine is currently driving my QRSS beacon ?which is currently QRV on 10,140,050 MHz with 250mW to an indoor attic dipole.
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73 Hans G0UPL
Ron,
????????Reminds me of the old days as a youngster building Valve VFO, enclosing it in a box etc.. For PSK: I suggest that you take this requirement to the another extreme and build a DDS VFO !!! Not Joking, its actually the best of both worlds.. Its tough to make a VFO with 10Hz stability.
????????Try replacing the 56pf next to Q5 with polystyrene.. it should give your major improvement.
????????No recent experience with digital. I used to run a bbs till some years ago..
73 Raj
vu2zap
At 03/02/2005, you wrote:
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