gary wrote:I regard the tx on NBTV a "miracle" though, not because of the limited bandwidth (which is problematic enough) but because of the horrifically low signal to noise ratio and propagation/phasing distortion of amateur bands. None-the-less Vic's VSB system seems to give markedly improved results.
I cannot find technical information on the VIC's VSB system, such as the frequency it operated, but VSB like DSB has the problem that two VSB rigs cannot communicate directly, since the two sidebands will present as the receiving frequency in the receiver. Only an SSB can distinguish the signal transmitted from a VSB station.
Anyway, here is another idea that came to my mind.
What if one could modify feld hell, for the purpose of nbtv?
In hell, the image is scanned and printed dot by dot in a line, just like nbtv.
The problem of synchronization could be fixed by the sync pulse, or without a sync pulse, by manual adjustments on the RX.
The only real problem I see is that the frame rate must be more limited and the fact that instead of two levels (on/off) we have to find a way to present the different brightness levels.
In hell, this can be done by limiting the signal strength, but the system would not be in fact a pure on/of but an AM with clearly defined power levels.
Just an idea...
By the way, fldigi using feld hell x5 gives a distinguishable BW image and I guess it is about 0.5fps, and the bandwidth is only about 1.2KHz judging from the waterfall, not a real time video though but not very bad for that bandwidth.