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 » Tue Jan 28, 2020 3:56 pm

On a different note, though certainly applicable here, anyone know where to get CA3308 ADCs? They're the 8-bit version of the 6-bit CA3306 ADC used in converting FSTV to NBTV or SSTV. There are other more modern variants around but none quite match the speed and simplicity of these two devices. I have the datasheets for both and they work in exactly the same manner and at the same speeds, the CA3308 simply has two more bits...pdf attached...

I have trawled the 'net without much success, but I'll keep trying...though I'm open to other devices/suggestions...

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

Postby Klaas Robers » Tue Jan 28, 2020 7:02 pm

I tried Conrad, as they sometimes have still older ICs. But no CA3308 or CA3306 known.....
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Re: NBTV/SSTV-625 Up Converter MkIII

Postby Harry Dalek » Tue Jan 28, 2020 7:44 pm

I found these same code but not what you are after
https://www.ebay.com.au/itm/CA3308T-IC- ... ctupt=true


What about these ?
https://www.ic2ic.com/search.jsp?sSearc ... 8&prefix=C

What about the CA3306 ? is that the same thing ?

https://www.aliexpress.com/af/ca3306.ht ... 0128005153
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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 » Wed Jan 29, 2020 1:46 pm

Thanks for the effort Harry but I already have a few CA3306's, they are the 6-bit version. I'm hoping to find the 8-bit version, CA3308.

The photo shows a T099 device and although the type number looks correct, they can't be, the CA3308 is in a 24-pin 0.6" DIL package, so who knows what those TO99 devices are! And look at the shipping, ridiculous for something that weighs only a few grams!

Thanks again Harry but I'll keep looking.

If I can't find any I'll simply have to use a more recent device...

Though two CA3306's can be cascaded to form a 7-bit ADC which may be OK.

The Maxim MAX1191 is ideal and a sane price, but in a SMD package which is one of the most human-unfriendly types, SOIC is OK, but not this!

Steve A.

Crappy photos on that site, why did they bother? Here's a similar photo I just took using my inexpensive Vivo 'phone...f2.2, 1/33s, ISO400, 31mm focal length, hand-held. The markings (LM357 etc.) are on the side of the device...the coin is 20mm in diameter, a 1 Baht coin from here...around three cents US.
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Re: NBTV/SSTV-625 Up Converter MkIII

Postby Steve Anderson » Fri Feb 07, 2020 4:31 pm

Gents, I have a confession to make and I cannot believe that others haven't picked up on my stupid error!

For this SSTV (or NBTV) converter to 625 we DO NOT need a fast A-D. The internal A-Ds in the PICs are plenty fast enough and 10-bit. What in the heck was I thinking of? That's if we need an A-D, if we use the pulse duration method to measure the SSTV frequency we don't need an A-D at all, just a comparator, also within the PICs.

So all that previous stuff about CA3306's and CA3308's is a load of old twaddle!

I think the Christmas and New Year spirit must have got to me! (Weak excuse). Unless I was prattling on about something else, i.e. somewhat off-topic, which is nothing unusual for me!

In my defense I have got the circuit diagrams correct, I must have some corrupted neurons in the grey matter!

Steve A.

Note to self: Keep it on-topic in future!...and THINK before you post!

Ah! My posting here of Jan 28 does actually exonerate me! All the same I can't think why I was looking for these devices...NURSE!
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Re: NBTV/SSTV-625 Up Converter MkIII

Postby Harry Dalek » Fri Feb 07, 2020 6:25 pm

That's Ok Steve mistakes are a good thing never learn a thing without them ~! Just watching seeing how it go's less ic's are a good thing !
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 » Fri Feb 07, 2020 7:22 pm

Keep up the good work Steve. Looking forward to your progress.

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

Postby Steve Anderson » Thu Feb 13, 2020 4:26 pm

Sadly work on this MKIII Up-Converter has almost ground to a halt due to a large work project I'm involved in. Location - The Maldives, yea, that's OK, I'll suffer it for a while...

When i get time I'll continue on with the design phase, but with no workshop I can't prototype anything...

But anyway, in the past there's been discussion of the use of 525 lines as a source of down-converted material to SSTV. If you look at the 525 line/field/frame spec attached there are 242 complete lines in an NTSC field (Field 1 or 3). If we use every other line and only use 120 of them then append eight lines of greyscale (or anything else), we end up with a 128-line SSTV picture. If not we still end up with the Cop McDonald 120-line standard, either at EU or US SSTV format.

Now the hiccup may be that inexpensive TV cameras may not adhere to these broadcast standards - there's only one way to find out...

Steve A.

625 down-conversion is comparatively easy...and doesn't require the greyscale, but can be added if required.

The attached was from this site...If interested I suggest you download all you might need in the future before it vanishes...(Windoze - right click - save as..Webpage or Website complete, HTML).

https://web.archive.org/web/20080220113 ... index.html

For NBTV'ers I still have that in mind and it should be comparatively simple...except if you are in a 60Hz country, that's awkward...
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DAVTREND MODEL DRAE

Postby acl » Tue Aug 11, 2020 2:38 am

Hi there all,

Has anybody a schematic diagram for this beast. I bought one off eBay some time ago and it died on me.

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

Postby Steve Anderson » Tue Aug 11, 2020 3:32 pm

Davtrend are still in Portsmouth UK, but seem to only manufacture power supplies these days. It appears in the past they went into bankruptcy/receivership. No harm in giving then a call, there may be a sympathetic soul there that could help. A quick Google should find them. They don't seem to have a website though.

Steve A.

Hmm...maybe it's too late after all..

1580 Parkway, Solent Business Park, Whiteley Fareham, Hampshire, PO15 7AG
Company status Dissolved
Dissolved on 14 May 2020
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Re: NBTV/SSTV-625 Up Converter MkIII

Postby acl » Tue Aug 11, 2020 8:45 pm

Thanks Steve for the information. Just an idea but could you just use a series of comparitors to do the 'front end job' of the a to d conversion on the SSTV convertor ? then feed to a port

The LM3914 / LM3915 / LM3916 are identical except for the ten resistor divider inside each part.

LM3914 - linear steps, scaled by a resistor divider consisting of ten 1000 ohm resistors.[1]
LM3915 - 3dB logarithmic steps, scaled by a resistor divider consisting of 6630, 4690, 3310, 2340, 1660, 1170, 830, 590, 410, 1000 ohm resistors.[2]
LM3916 - VU-meter steps, scaled by a resistor divider consisting of 1087, 970, 864, 769, 1298, 1031, 819, 923, 1531, 708 ohm resistors.[3]
All the devices in this group operate with a range of voltages from 3-35 V, can drive LED and VFD displays.[4] They can provide a regulated output current between 2-30 mA to directly drive displays.

Internally, each device contains ten comparators and a resistor scaling network, as well as a 1.25 volt reference source. As the input voltage increases, each comparator turns on. The device can be configured for either a bar-graph mode, where all lower-output terminals switch on, or "dot" mode in which only one output goes on. [5] The device is packaged in an 18 pin dual in-line package or in a surface mount leadless chip carrier.
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Re: NBTV/SSTV-625 Up Converter MkIII

Postby Steve Anderson » Wed Aug 12, 2020 1:38 pm

The problem with the LM391x series is probably the response speed, so much so that it's not even mentioned in the datasheet! They are designed as a display driver for human eyes so it would only need a response time of milliseconds, not the nanoseconds we're needing here. With only 10 levels per chip you'd need several of them to get any reasonable quality video. (This is in the context of down-converting 625 to NBTV or SSTV).

The CA3306 was a good choice as it can sample up to 15MHz (7.5MHz bandwidth) even though only 6-bits. There is/was the CA3308 much the same but 8-bits, but they're even harder to find than the 3306...and where quoted at US$75 each! I think I'll give it a miss.

For SSTV/NBTV-625 the internal A-D of the PIC micros are fast enough, around 50kHz sampling depending on oscillator frequency, and 10-bit, though I only used 8-bits in the MkI version.

On the output side I used a DA-08 D-A (or one of its variants) which has a quoted response/settling time of 100ns though rather oddly I didn't measure it...something to add to my 'to do' list. On the MkIII version I've now changed the D-A output stage to a common-base configuration which may help with the output speed...not that it seemed lacking in the MkI.

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

Postby Klaas Robers » Wed Aug 12, 2020 7:33 pm

Steve, I told this earlier: 6 bits is sufficient for video, as long as you provide that video black to white covers almost the range from h00 to h3F. In the far past, say 1975, I did experiments on that at Philips Research. So, if you amplify and clamp the signal in the analogue path, such that black gives you e.g h04 and white gives h3B (a bottom and top margin of 4), then you will not see the contouring caused by the quantisation.
If you want to include the sync as well, or you want not to clamp the signal before A to D (AC-coupling), then you need 7 bits. This is all for black and white.

You might remind that the Robot model 400 SSTV scanconverter uses just 4 bits. Then contouring due to the quantisation is well visible. Then when going to 5 bits would give a considerable improvement, and going to 6 bits makes it invisible. A doubling of the number of steps does a lot!

However, in SSTV practice there is always quite some noise in the received radio signal, which will make the quantisation, even of just 4 bits, almost invisible. I did my Philips experiments with signals coming from the studio flying spot slide scanner, they were noise free on the B&W studio monitors.
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Re: NBTV/SSTV-625 Up Converter MkIII

Postby Steve Anderson » Thu Aug 13, 2020 7:06 pm

An update on the MkIII SSTV/NBTV-625 up-converter RAM and output stage.

Much fewer connections required for the RAM and (I hope) an improved output arrangement, it now can feed two 75R destinations, monitor and 'scope perhaps. The sim calculates the output stage should be about -1db at 10MHz - plenty good enough!.

The use of the Vlc input could be viewed as a bit cunning, in the MKI I used a eight AND gates to do the blanking. Vlc controls the switching levels of the D-A. When at 0v the chip recognizes 1.2v as the difference between '0' and '1' on the data inputs. If you put 3.3v on it from the micro the switching level becomes 4.5v - which the micros cannot produce, therefore any activity on the data lines is ignored...blanking while the RAM s being written to. That's the theory anyway. My only concern may be there's no speed mentioned in the datasheet for this input, but looking at the internal schematic it should be much the same as the other inputs. Plus a 'guard band' in terms of time of a few microseconds either side of the read function may help too.

Steve A.

Not sure why when posting a diagram like this it becomes 'fuzzy' here, the original is fine...unless it's too large pixel wise and the server reduces it...rather poorly at that. When all done I'll zip all the drawings in the original high resolution GIFs and post them/it here. If you download a free Autocad viewer you can see them in native quality. I'll post the 'dwg files if anyone is interested, these are Autocad 2016 files.

Anything in blue is just notes to myself - ignore...

For those that wish a NBTV-625 converter this part can be exactly the same. In fact the majority of the rest could be the same as this SSTV-625 up-converter. The difference would be in the input circuitry and the software...it's something I've had on my mind for a while, a dual function device.
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SSTV-625 MkIII Main 1 v3 Model.gif
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NBTV/SSTV-625 Up Converter MkIII

Postby acl » Thu Aug 13, 2020 9:15 pm

Thanks Steve,

Look forward to further updates

Chris Lewis
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