Moderators: Dave Moll, Andrew Davie, Steve Anderson
Harry Dalek wrote:I was wondering how wide the bandwidth would be if there was a FM version of NBTV as in speeding up SSTV to a movement version ,i should not have these thoughts Sacrilege!
Steve Anderson wrote:It can be done, technically. The problem becomes one of how to transmit or record/playback the resulting signal?
In very rough numbers SSTV requires 1kHz of video bandwidth, NBTV 10kHz. Keeping line-standards/frame-rates the same and crudely multiplying everything by a factor of 10, NBTVFM (we'll call it that for now) would have sync at 12kHz and white at 23kHz. It would be better though to raise these numbers somewhat, but we'll stick with them for now.
These days a PC sound card sampling at 48kHz could just manage it, far better at 96kHz. So for PCs - plausable to possible.
But transmitting? I don't think so. Another 'standard' - there are enough already. Special transmitters/receivers etc, but if the amateur community really wanted it...why not?
The great advantage FM as per SSTV is response down to DC. No more DC restorers, no more LF headaches, but standard domestic audio gear just cannot handle it...and that's in a way what configured NBTV as we know it and as well as the technology of the 30s era which defined it in the first place.
If two or more people wanted to develop this, it can be done, but without wide acceptance 'standards' die.
Steve A.
Steve Anderson wrote:Harry, can I ask a favour of you...
I've created the first wave-file generated by the DDS modulator. The video (baseband) was from the same development board I used earlier on when I started on this. When you listen to it all sounds fine. I've checked the line timings (US 15Hz, 120-lines) and they're spot-on.
I tried to use MMSSTV and using the auto-slant thing it sort-of achieved line sync but it never seemed to find the frame sync. The frequencies are 'close enough' in the spectum window.
I've never used MMSSTV before so maybe it's something I'm not doing right...very possible.
So could you have a look at this if you can spare some time? (But not too much). It's a fairly small wave-file due to the 8kHz sample rate, only sixty seconds or so and mono. Also, the best I was able to achieve in MMSSTV is below...
Steve A.
I've check the frame timing now, eight seconds it is....
Steve Anderson wrote:Harry, I think it may be that used a sample rate for the wave file that MMSSTV doesn't support. Let me look into it further, don't waste any more time on that version..
I'll delete the previous attachment...done...
I'll do another one and check the results by playing it back in MMSSTV first...
Steve A.
Steve Anderson wrote:Ah!! MMSSTV can't play wave-files it seems, only its own format (.mmv), at least in the version I have, 1.13A.
But thanks for your effort Harry...shame it didn't work out....
Steve A.
Steve Anderson wrote:What I'll do tomorrow (Friday) is knock-up a simple decoder on the breadboard and confirm or otherwise that what I'm generating is valid.
After that, if you can tell me the correct sample rates for .wav files that can be viewed by the software you have (or converted) we'll have another try. Please don't spend any more time on that original file...
Thanks Harry.
Steve A.
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