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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

-----Original Message-----
From: Raj [mailto:ggrk@...]
Sent: 03 February 2005 15:04
To: BITX20@...
Subject: Re: [BITX20] Stability?


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:

I really appreciate your quick reply Raj,
No you did not confuse me.
This forum is alive !
Yes I used the ceramic ones for initial trails. I have some polysterene ones (old!! from Philips radios) in my junkbox and will do some trials coming days.
What is your feeling about making the 2 transistor vfo as shown in the original schematics working with a freq. drift of 10Hz or less (this is a tough requirement for digimodes like psk31).
Is there experience with the bitx working with digimodes (rtty, psk31...) as far as you know?
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73 and again tnx fer advice!
Ron


Raj wrote:

Ron,


???????? This is probably because of ceramic capacitors being used the

oscillator stages. Components that determine frequency must be ultra-stabe.

Use NP0 caps, brown ceramics with a black top. You can also use

polystyrene, they are transparent plastic with a silver foil visible

inside. They were only available in the old days in small pF values less

than 5Kpf.


???????? I usually pour bees wax on top of oscillator components to keep

them thermally isolated and keep them from shaking.


???????? Avoid ceramic caps in audio stages, it causes microphonics. Tap

them and you will hear a thump in the speaker/transmission. Use

mylar/polyester.


???????? Do not use mylar/polyester type caps in RF stages for bypass,

instead use ceramic. Polyester work well in audio for coupling.


???????? Ceramic = brown round disks

???????? Polyester/Mylar = green like a chewing gum with leads.


???????? Hope I have not confused you..


73 Raj

vu2zap


>MHz IF will give the proper range) Frequency range seems to be ok but

>stability is bad. After 20 minutes waiting freq shift of 1 KHz still

>exists. I think I will order some components for a HuffAndPuff

>circuit for stabilizing purposes.

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