Hello David, I see it as an alternative to bit stuffing. Both are methods designed to improve the demodulation.
I think the HDLC AFSK was standard for 1200 but it seems every higher bit rate went with a scrambler. Maybe since they were already high bandwidth for the channel, it reduced co-channel interference. This particular scrambler has a minimum complexity, and designed for frames of data. I think that BER shouldn't be worse, but the spectrum power should be more uniform. No beeps and squawks. It sounds like white noise. If you listen to the original modem audio it has a beat to it, where the scrambled does not. The Sync symbols will have to be sent unscrambled obviously. FM isn't designed for long range anyway, it is a wide-band mode much like AM with double side-bands, converting the 6 kbps into 20 kHz for transmission. If it's not full quieting, you are probably going to need more power, which is cheap at class-C. Steve On Sun, Apr 12, 2020 at 3:14 PM David Rowe <[email protected]> wrote: > Hi Steve and Jeroen, > > I was wondering why you wanted to use a scrambler? > > I understand the main reason is making the synchronisation algorithms > work better. For example if your data source is all 1's, the timing > estimator can't work out where each bit stops and starts. > > Anyhoo, if it does make a difference in your application, you'll see it > in the BER results. > > Thanks, > David >
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