Klaas Robers wrote:Steve, your problem is: time. Good luck.!
Steve Anderson wrote:Klaas, I guess you could break down the objectives into two major chunks:-
1) Improve/replace the Robot 70 SSTV-analogue demodulator, to an extent I would like to think the 'improvement' phase has been achieved...however there's more that can be done here...which is the 'replace' stage.
2) Reduce the complexity of the MkI up-converter...currently work in progress...
If as you mention you have a P7 SSTV monitor you'd possibly be only interested in the first item. I've got a few P7 CRT's here, one day I'll get around to using them!
Steve A.
Harry Dalek wrote:...any case what i am getting at here is the 70 year old HV transformer is still going strong while the 1990s low voltage Torriod is dead just shows you .
Steve Anderson wrote:Harry Dalek wrote:...any case what i am getting at here is the 70 year old HV transformer is still going strong while the 1990s low voltage Torriod is dead just shows you .
Yep, no surprise there!
When I do get around to a P7 CRT SSTV monitor I'll probably use a bit of each technology, say the demodulator as mentioned here and valves/tubes for deflection and cathode/grid drive. A hybrid using bits where best suited, I'm not aiming for something that can be put in your pocket or run off batteries! (Well maybe a car battery, I do have a 300W/240V inverter in the car...).
Steve A.
Harry Dalek wrote:I hope you do make one, be interested to see it come together and your demodulator is in mine...just remade it for the record lathe.
"Steve Anderson
Er...why Harry? Unless you mean for playback. I venture to say that you'll get nowhere trying to record the baseband (demodulated) signal. Record the SSTV sub-carrier, that's OK...the 1200-2300Hz signal.
Although the revised Robot 70 demodulator isn't perfect, it actually does quite a good job. Yes, it could be better, especially 'that' output filter - but I take responsibility for that, it wasn't part of Robot's original design. A large part of the reason I'm working on a replacement currently.
I did buy the 3" and 5" CRTs some years ago specifically for NBTV and SSTV use. They've been sat on my shelves all that time...time to pull my finger out...
Steve A.
Harry Dalek wrote:It did cross my mind to record the base band ! sounds like its a bad idea !
Steve Anderson wrote:
Just like NBTV the problem becomes one of LF response - except far worse! ...In the milli-Hertz range, that's the reason why SSTV is modulated onto a sub-carrier.
When it comes to extracting syncs here's my understanding of the standards involved for the EU format, either 120 or 128 lines. The US variety will simply have a slightly longer line-time of 66.7ms.
Steve A.
Steve Anderson wrote:Well, there's no reason a system cannot be made dual standard for US/EU rates, it's actually quite simple...so why not? Some are lazy and ignore the rest of the world...I wonder who?
Today the recording and playback of NBTV is quite easy - down to DC frequencies - actually DC isn't a frequency at all...I digress..
A simple sound-card (or its modern equivalent) will do the job. If it can sample at 48kHz or 96kHz you're in business! If you wish to include sound then you have a few decisions to make...but for SSTV 8kHz sampling is enough, which in the audio world is viewed as telephone quality. No great demands made on the hardware, and most RS232 interfaces should be able to handle it where needed.
If you consider the SSTV bandwidth being 1kHz and the NBTV bandwidth being 10kHz, there's no reason why a subcarrier-based NBTV system of 12-23khz shouldn't work fine. No good for phone-lines or HF comms, but it is a possibility, though I'm NOT suggesting it as a standard...there are enough already!
Steve A.
Harry Dalek wrote: Well i agree rather use our mains frequency standard divided to our SSTV standard line frequency ..but software is lacking i think i still have one DOS program that does both 8 and and 7 sec only one i have ever seen must of been posted up some where .
Any case it reason i use the 8 sec only because i can test my recordings ...
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