HackTV - Analogue TV transmitter for the HackRF

[djrm]

Greetings everyone,
I'm not getting on very well building Frank's standards convertor, I'm well impressed by the results I've seen posted here on the forum but its going to take me a while yet to get finished..

In the meantime I've seen this design for a direct synthesis 405 line TV transmitter. It uses an open source SDR transmitter module called Hackrf. I've been interested in these for a while and now Ive seen the 405 line capable transmitter has already been designed I've ordered one to try.

Here is a link to the software etc: Hacktv
I see it may also be used to transmit teletext, this and Prestel are quite interesting old technogies I experiment with from time to time.
I have an old Alcatel modem terminal which can connect to an online service here: Viewdata using a simple ESP8266 serial to wifi adapter.

Kind regards, David.

[Murphyv310]

Hi David.
I read a thread on the UKVRRR about this but from what I can gather it isn't proper system A. You would need another HackRf for sound (PAL has inter carrier sound) and also standards conversion to 405 lines with positive modulation.
If I'm wrong then I apologise. I think I'd like to see one working before parting with any cash.

[djrm]

Hi Trevor,
The software does produce some kind of sound, but it looks to be limited in some way. I think it is amazing that it can generate a picture and sound at all. I'll wait and see what the quality is like when the device arrives, it may take a while for it to arrive here. David.

[Murphyv310]

Hi.
Here is a link to the thread on the UKVRRR.
https://www.vintage-radio.net/forum/show...p?t=141810

[Murphyv310]

There are other ways of course to provide a 405 line signal to a set.
There are a couple of circuits for Band 1 modulators using the MC1496 modulator chip, David Looser's one is simple and effective, see here: http://www.thevalvepage.com/projects/mod...odulat.htm
Then you could try Peter Scott's PC solution, probably the cheapest route.

[ppppenguin]

I thought Peter Scott's solution was to do with devising modelines for graphics cards so they could produce non-standard video output such as 405. I don't think it was for RF. I know that Fabrice Bellard devised a solution for RF generation using a PC graphics card.

For System A modulation I know of these approaches:

Conventional modulators using MC1496 balanced modulator chips. Such as those by David Looser and myself.
Conventional modulator using discretes. Such as that by Darius.
Synthesised modulator using Freescale (previously Motorola) MC44BS373CA chips which are now getting harder to find. This was first done by David Robinson in his "one off" converter. This method was later used in the Aurora and Hedghog converters. A pair of chips is needed, one for vision, one for sound. A single chip can't quite manage both.
I don't know if anyone has successfully synthesised a modulated System A signal using a PC

Darryl (the Aurora man) and I discussed direct synthesis using an FPGA. It never went further than a few ideas and calculations. I'm sure it's possible but not necessarily simple or easy.

[Murphyv310]

Hi Jeffrey.
I think you have misread my post. You still would need a modulator to display the PC standards conversion on a 405 line TV unless you take the less safe route of baseband Video and Audio, I never got round to doing it as my old PC ate two graphics cards and I lost heart. Eventually the old PC went faulty with a catastrophic failure and the thought of yet another graphics card was out of the window.
Peter gives very good details how to do this along with a small sync circuit and the correct way to combine RGB signals from the VGA output.
It is possible to get the Raspberry Pi to transmit and as we know can do Station Ident and RDS on FM, it also can do DVB but I really doubt it would do 405 with video content, possibly stills.
I firmly believe that the simplest way to show quality programs on a 405 line set is with a dedicated standards converter like the Aurora and Hedghog, the PC idea is also good but probably more work and less simple to do, plus the addition of a modulator.

[Terry]

I'm reminded of an idea I played around with some time ago but, as far as I can remember, never posted anywhere.

There have been a couple of requests in the past for help in producing signals on two adjacent channels - B4 and B5 come to mind.

The problem is that this will require a VSB modulator for the lower channel.

One day I stumbled on the spec for an 8MHz channel pass SAW filter, which prompted the idea. It was to construct an IF modulator using such a filter - recovered from a scrap DTV Set Top Box, perhaps - then add a local oscillator to up-convert the IF signal to the required channel.

What does the team think?

   

[ppppenguin]

Ought to work, so long as the up-converter is nicely linear.

The other way is a fully fledged VSB filter which is a lot more complicated than an off-the-shelf SAW. Darius designed a VSB filter for his modulator but this is all the data I have. Aligning a VSB filter accurately really needs a vector network analyser, something most of us don't have.  The group delay matters a lot, so an ordinary frequency sweep or white noise test isn't really good enough.

We've discussed direct digital synthesis of RF, such as Fabrice Bellard's work. I wonder if that could do a decent job of VSB.

[djrm]

Hi everyone,
The Hackrf arrived today and I couldn't wait to try it.
The video picture could be better but I have streamed net video onto a 405 line TV with it.
I have heard sound only on 625 line colour pictures, not on 404 line B&W.
I like the teletext server part the best though.
Kind regards, David.