NBTV/SSTV-625 Up Converter MkIII

Where it all started as far as most are concerned and saw heavy use from the 60s through to the 80s. Colour and Hi-res modes have unfortunately pushed this system into the backwaters of SSTV. Time to resurrect interest in this simple analogue system.

Re: NBTV/SSTV-625 Up Converter MkIII

Postby Steve Anderson » Sun May 14, 2017 9:17 pm

Yes, I recall I2L (I squared L) but have never used the devices fabricated with it. Not sure which came first but the ZNA234 TV SPG and signal generator was widely used, though monochrome only. A few clever people did glue on the required colour stuff to it, but it was never that good.

Anyway, I've been informed the processor chips I need have arrived, so rains permitting I'm off across town tomorrow to get a bunch (the wet season here has just started, 57mm yesterday, nothing much really).

Steve A.
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Re: NBTV/SSTV-625 Up Converter MkIII

Postby Steve Anderson » Wed May 17, 2017 3:37 pm

No sane chance to get across town due to the rains, 97mm yesterday. Quite a bit this morning and Chinatown, which I have to go though, is flooded....real annoying!!

There is also a chance I may be off to Doha, Qatar, for a while at the weekend.

Steve A.

Friday, 19th. Qatar trip still not organised, weather forecast for next week looks better than the last few days.
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Re: NBTV/SSTV-625 Up Converter MkIII

Postby Steve Anderson » Mon May 22, 2017 8:38 pm

At long last I got across town without getting drenched and now have the processor chips I need. So now I can really get on with things....

First off is the 625 sync and VBI waveform generation, should be a straight forward port from the MlI with adjustments for the double-speed clock. Then the 'acid-test' on my blanking idea. Though it's possible they may be done in the reverse order...

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Re: NBTV/SSTV-625 Up Converter MkIII

Postby acl » Tue May 23, 2017 3:53 am

Good luck Steve,

We thought you were going away last weekend. My next job is mid June. Let us know when you are happy with the hardware configuration so we can make a start. I'm just starting checking the demodulator section and realise that in order to check it 100% with a SSTV signal there are certain enable signals from the processor side to prove it fully. I will let you know how I get on.

Regards Chris Lewis
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Re: NBTV/SSTV-625 Up Converter MkIII

Postby Steve Anderson » Tue May 23, 2017 11:57 am

Chris, the modified Robot 70 demodulator which you are building is a stand-alone device and requires no control or feedback from downstream circuits. You should be able to find any faults (hopefully none) and view the baseband SSTV signal at the output on an oscilloscope.

I'll make a start today on testing the rest of the circuitry and the writing the software.

As for the trip away, no news on that at this point. So often there's a mad panic for me to be somewhere, then it all goes quiet - until the next panic.

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Re: NBTV/SSTV-625 Up Converter MkIII

Postby acl » Tue May 23, 2017 8:35 pm

Sorry Steve I didn't look at the decoder circuit correctly. I thought the outgoing terminals were connected to the microprocessor board. Reading it more closely I realise these are internal connections and the board can be tested in isolation and by feeding SSTV audio in I should be able to set the two pots to give me the correct output signal .

Empty head Lewis
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Re: NBTV/SSTV-625 Up Converter MkIII

Postby Harry Dalek » Tue May 23, 2017 8:48 pm

acl wrote:Sorry Steve I didn't look at the decoder circuit correctly. I thought the outgoing terminals were connected to the microprocessor board. Reading it more closely I realise these are internal connections and the board can be tested in isolation and by feeding SSTV audio in I should be able to set the two pots to give me the correct output signal .

Empty head Lewis


Hi Chris

I used the circuit in my SSTV works very well i would use Steves SSTV reversing wav file the staircase is very easy to read on the scope ...
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: NBTV/SSTV-625 Up Converter MkIII

Postby Steve Anderson » Tue May 23, 2017 9:00 pm

One of the reasons I use those 'blocked in arrows' with !A, 6H or whatever inside is reduce the width of the drawing so that it's still legible with an 800-pixel width to fit this board for most users. To an extent that also applies to the newsletter. A long thin left-to-right drawing is hard to fit within an A4 page, even if rotated sideways. I also annotate to where or from where the signal comes or goes.

The direction, which way the arrow is pointing, also indicates if it's a source or destination. I haven't yet defined a bi-directional signal 'arrow', say for a RS485 or I2C circuit. I have tried a double-ended 'arrow', but it doesn't look right to me...I'll think of something when the time comes. Maybe just a square block, one could say gender-neutral. The annotation would read, "TO/FROM IC504, 6 (or whatever)". Chip number first, then pin number and optionally a pin function, e.g. RB7 (on a micro). Or simply,"TO/FROM R174".

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Re: NBTV/SSTV-625 Up Converter MkIII

Postby Steve Anderson » Sat Jun 17, 2017 5:10 pm

Things have been getting in the way on this, but I hope to resume in the next few days. I'm sitting at the airport waiting to board my flight back home. I have a report to write up then it's back on this in anger...until something else comes along...

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Re: NBTV/SSTV-625 Up Converter MkIII

Postby acl » Sat Jun 17, 2017 6:08 pm

Looking forward to your progress Steve. Could you point me to the 'reverse staircase' SSTV signal so I can test the demodulator when you have some time.

Regards Chris Lewis
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Re: NBTV/SSTV-625 Up Converter MkIII

Postby Harry Dalek » Sun Jun 18, 2017 9:43 pm

acl wrote:Looking forward to your progress Steve. Could you point me to the 'reverse staircase' SSTV signal so I can test the demodulator when you have some time.

Regards Chris Lewis


I had them on file chris ,i recall klass and steve testing different bit rates quality for best results.
Attachments
Reversing Bars 8-level 120 EU 8-bit 8kHz 1.wav
(468.88 KiB) Downloaded 14 times
Reversing Bars 8-level 120 EU 8-bit 12kHz 1.wav
(703.25 KiB) Downloaded 14 times
Reversing Bars 8-level 120 EU 16-bit 12kHz 1.wav
(1.37 MiB) Downloaded 14 times
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: NBTV/SSTV-625 Up Converter MkIII

Postby acl » Sun Jun 18, 2017 9:51 pm

Thanks
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Re: NBTV/SSTV-625 Up Converter MkIII

Postby Steve Anderson » Mon Jun 19, 2017 4:14 pm

Thanks for doing that Harry, I am still running around chasing up things that need to be completed soon.

In the end no difference was noticed between the different bit-depths or sample rates, at least with the existing demodulator.

Steve A.
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Re: NBTV/SSTV-625 Up Converter MkIII

Postby Harry Dalek » Mon Jun 19, 2017 6:55 pm

Steve Anderson wrote:Thanks for doing that Harry, I am still running around chasing up things that need to be completed soon.

In the end no difference was noticed between the different bit-depths or sample rates, at least with the existing demodulator.

Steve A.


Thats Ok Steve i was thinking you may have been on another work trip .
Chris when i was testing mine it was done on the forum on the Deep image SSTV monitor posts have a look may help you out testing yours .
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: NBTV/SSTV-625 Up Converter MkIII

Postby Steve Anderson » Mon Jun 19, 2017 8:44 pm

As this MkIII up-converter is migrating to a 3.3V supply I not only needed to modify the existing supply (done), but I'll have to modify the (my) demodulator output levels. I have posted these already but I will do so once again as a final version once I have completed the modifications here. In doing so it removes one gain stage which isn't required any more.

I can't see me going away anytime soon but something is looming on the horizon...

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