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Re: LF: Generating 8970 Hz carrier with Spectrum Lab ?

To: [email protected]
Subject: Re: LF: Generating 8970 Hz carrier with Spectrum Lab ?
From: Andy Talbot <[email protected]>
Date: Fri, 27 Apr 2012 12:31:43 +0000
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You can generate accurate 8970Hz frequencies from a single PIC DDS provided you clock it with a decent source to start with.   The surplus market is awash with suitable oscillators as a reference, and the exact starting frequency does not even matter provided it it within the range for the PIC, so 5 - 20MHz will do.
 
See http://www.g4jnt.com/PIC_DDS.pdf  for a DDS based on 16F268 using an external R-2R ladder.   8 bit DDS resolution (spurii typically -45dBc) and 32 bit DDS resolution, with an internally generated clock in the 100kHz region, so output frequency setting to 23uHz  and a stability whatever the input allows.   A off-the-shelf typical TCXO with 1ppm stability is good for 9mHz  8970Hz
 
It will offer you FSK so instead of on-off keying you can implement DFCW, WSPR or whatever.
 
Andy
 

 
On 27 April 2012 12:01, wolf_dl4yhf <[email protected]> wrote:
Hello Peter, Stefan and all,

From the curved traces visible in Peter's high-resolution spectrogram I'd say this thermal drift is normal for a soundcard.
You may be able to shorten the initial time (after a "cold start" in the true sense) by setting the tolerance range (in ppm of the soundcard's "calibrated" sampling) to a much larger value. Markus DF6NM pointed this out a few weeks ago.
>From the "Components" menu, select "Sampling Rate Detector". There's a field labelled 'Max deviation from initial sample rate'. Be generous if your soundcard oscillator drifts fast and 'far', for example enter 10000 ppm in that field.

All the best,
  Wolf (@ DF0WD this evening, hoping for some crossband activity 500 kHz / 35XX kHz).


Am 27.04.2012 11:22, schrieb PA1SDB, Peter:
Hello Stefan, VLF,
I think you are very lucky with a PC that generates such a stable signal.
 
>Here i used a more than 10 year old notebook. Also if people like to use the digimode
>termninal or also the frequency generator, not beeing limited to frequencies given by the
>steps of a divider, SpecLab is much more comfortable. Also on the receive side i
>remember to have received DF6NM's first tests in a 47 uHz window, with a stable trace. :-)
>
>73, Stefan
I tried two notebooks now. That one where I was talking about yesterday is also a 10 year old Acer. Nice to see here (grab below) how good that "Sampling rate detector" works. In the first few hours I forgot to un-set the "measure only" option.... The signal drifts all over the graph. Then it stabillizes when I did the adjustment in the cfg.
Unfortunately that 2th PC that I test here, a "modern" 2 year old Acer Extensa 5235 notebook generates also a terrible trace at 47uHz.
 
 
One more PC to go :-)
 
73's , Peter - PA1SDB
 
 



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