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do we still use UHF modulators ?

Posted: Tue Mar 13, 2018 6:53 pm
by Andy Rea
As some of you may know i am developing a new ULA replacement.

so should it be able to drive the UHF modlator? Or is composite video only ok.

Regards Andy

Re: do we still use UHF modulators ?

Posted: Tue Mar 13, 2018 7:59 pm
by gammaray
UHF/VHF across the pond. Compatibility...?

I guess I could buy extra '1000's for parts.

Re: do we still use UHF modulators ?

Posted: Tue Mar 13, 2018 9:36 pm
by McKlaud
Andy Rea wrote:
Tue Mar 13, 2018 6:53 pm
As some of you may know i am developing a new ULA replacement.

so should it be able to drive the UHF modlator? Or is composite video only ok.

Regards Andy
Hi Andy

In my ULA development I dropped compatibility with the modulator. However if you think about the 100% drop-in replacement for the original ULA you should leave the ability to drive the modulator.

Re: do we still use UHF modulators ?

Posted: Tue Mar 13, 2018 9:38 pm
by Moggy
GODDAMMIT!!! I didn't fight a war just to look at wavy lines...(Sorry wrong forum)

Compo-wotsit just fine for me young sir. :D

Plus I think most of us have Karl's super composite board fitted and there can't be many old B/W CRT sets floating about that would need the modulator.

Just my tuppence worth.

Re: do we still use UHF modulators ?

Posted: Tue Mar 13, 2018 9:47 pm
by McKlaud
Well, with some new ULA's replacement no any super composite board is needed. The ULA could drive a TV directly with the proper black level.

See this below

Re: do we still use UHF modulators ?

Posted: Tue Mar 13, 2018 9:48 pm
by Lardo Boffin
It was actually a tough call to vote for composite only as it does mean that broken zeddies which are not comp modded won’t be fixable with this ULA however I suspect that this will be a minority and most people given a choice would go composite!
I have bought a fairly large number of zeddies (I think around 20 having had a quick look at my eBay emails) while having a year of refurbishing and only found 1 out of them all where the UHF was actually usable even on a glass screen telly. All the rest produced from poor to impossible to read pictures.

Re: do we still use UHF modulators ?

Posted: Tue Mar 13, 2018 10:00 pm
by Paul
Would Modulator compatibility raise the cost of the ULA replacement significantly? Or is it the time required for development that makes you ask?
It would be better have at least one replacement ULA that could be a repair for Zeddies with broken ULAs and drive its Modulator.
Would it be possible to offer a addon that gives modulator compatibility?
Kind regards
Paul

Re: do we still use UHF modulators ?

Posted: Tue Mar 13, 2018 10:05 pm
by McKlaud
Paul,

In my case the cost is a secondary issue, because we are talking about difference in voltage levels at the pin 16 of the ULA only. The development time could be longer but I think, both variants are feasible.

Re: do we still use UHF modulators ?

Posted: Tue Mar 13, 2018 10:21 pm
by 1024MAK
Do I still use ZX81s using the UHF RF output, yes. But only because the LCD TV that I use makes a decent job of displaying ZX81 and ZX Spectrum UHF pictures. And, I normally only use this for testing machines that are 'new' to me. Of which have not been modified yet.

When doing anything else, I use ZX81s that output a composite video output. If the ZX81 has a Sinclair ULA, either my version of the composite video modification. Or one of PokeMons crystal clear modules (ZX8-CCB - that I can never remember the name of, sorry, have to look it up each time :oops: ).

One problem with using the UHF RF output, is the frequency of the carrier oscillator in the modulator drifts as the ZX81 (or ZX Spectrum) electronics warms it up. Meaning I have to channel hop my TV to the next channel (which is tuned to a slightly different frequency).

Mark

Re: do we still use UHF modulators ?

Posted: Tue Mar 13, 2018 10:46 pm
by McKlaud
Has anyone got any schematic diagram or datasheet of the UM1233 modulator? I would appreciate if you could share it, please.