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3810Re: Drift

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  • josephrot
    Apr 28 4:37 AM
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      Vince...

      RE: << ....monitoring HFDL the last few days and it is convenient to let the radio decode the messages overnight. Problem is, PC-HFDL decoder can only handle about +/- 85 Hz drift and the radio drifts more like 200 Hz or maybe more as the room cools off overnight. >>

      If we are talking HFDL as in High Frequency Data Link...for transponder and related use...ACARS ?
       
      The drift normally comes from two or so places, if you will. The PLL base oscillator and usually the IF chain.

      The Sangean 803 / RS DX-440 used an old (by today's standards) non-TXCO/non-OXCO time-base standard in the PLL, and warm-up drift is not "tragically terrible", but it is noticeable. A drift from cold start to say 20 min warm-up in ambient of around 75F/24C using that age of circuit, of 200Hz was not all that bad back then.

      Compare it to, say, the venerable Sat 800, that remains a rock-solid performer within its stated ambient temp range, rarely drifting more than 10-30Hz. Thus, Sangean 803 / RS DX-440 drift from a "cool" room to an ambient of perhaps 80F/27C is fully expected, and yes, HFDL/ACARS use will pose that situation as a glaring and obvious situation.

      The IF chain can introduce "drift" by virtue of temp drift of parts, the ambient temp changes, etc. It's something that we all almost never think about, but it's there, and could be very important to HFDL/ACARS use.

      In any event, if using the Sangean 803 / RS DX-440, in such "precision" use, the above has to be taken into account, as far as temp stabilization for receiver and any other HFDL/ACARS related hardware.

      Yes, one could re-work and replace the Sangean 803 / RS DX-440 PLL time-base with a modern-day more stable base oscillator, but at what expense, mess, will it all fit, etc.

      Joe Rotello / Knoxville, TN / USA


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