The future: DC mains

[Bob Eager]

Same here. But the three are all my region!

[SH]

I seem to recall that cars were originally positive earth, but this changed over to negative earth due to corrosion issues?

[Harry Bloomfield Esq]

The turrets were 405 line VHF, BBC2 came along it was on 625 line UHF and via a separate tuner. After the 405 VHF turrets, the dual standard sets came along able to tune both VHF and UHF. Eventually VHF was shut down, and all were on UHF, then along came colour.

[Harry Bloomfield Esq]

Thanks, I have only vague recollections of the era.

[Fredxx]

Not any more, they've been banned on new builds.

[Joe]

Back in the bad old baseband TV broadcast days, transmitted video was locked to an atomic standard, at least the BBC channels were. Mostly I used it to set camera master oscillators using a dual-channel scope, but it could also be used to genlock a Tektronix TV sync generator, which had a 10MHz output.

[Joe]

Possibly more to do with PNP transistors being superseded by NPN, for which a positive supply rail was easier to deal with. Also electronic ignition was beginning to appear, which used a large NPN transistor.

With dynamos and no onboard electronics, it was easy to reverse the car's polarity, but alternators were definitely of fixed polarity.

[Peter Able]

Just don't ask me about what happened 70 minutes ago !!

PA

[Peter Able]

AFAIK no turret tuners could be adapted to receive UHF. Dual Standard sets were awful bodges.

Good for the repair business, though. Those foot-long cheap slide switches. Quick spray with switch cleaner and a few operations of the switch. Take the call-out fee. "See you soon!"

PA

[Max Demian]

I believe that was the case.

This link seems to think there's not much pro or con:

[Colin Bignell]

It is a while since I have been on the canals. My late partner wouldn't steer and there came a point where she couldn't work the locks either.

[NY]

Except that VHF was shut down *after* the advent of colour. I think it finished some time in the 1980s, and colour began in the late 60s and became available on all transmitters (AFAIK) by the early 1970s.

[Harry Bloomfield Esq]

It was my own design of that, which I built and used. One LED to indicate power, another to indicate lock. Probably still on the shelf of my workshop, but useless now.

[Harry Bloomfield Esq]

Well, the main ones at least.

[Ian Jackson]

I understood that it is positive earth that gives less corrosion, but in vehicles they eventually found that, in practice, there was little difference.

[wrights...]

I can get every ITV region and every BBC region.

Bill

[Max Demian]

I assume UHF only TVs always used varicap tuning, usually with presets (except some portables).

[SH]

So you managed to get ITV Meridian and BBC South along with BBC 1 Wales and ITV Wales at your humble abode in Yorkshire using an amplified Yagi Uda quad phased array on a 20 m long pole then? :-D

[wrights...]

No, that wouldn't work. Instead I use a small sat dish and a cheap sat box.

Bill

[Ian Jackson]

Some of the early ones* did use the usual gang of variable capacitors, and continuously tuned the whole UHF band. But yes, varicaps enabled push-button switched multi-turn pots for preset channel selection.

*I've got three or four 'integrated' tuners from the late 60s. IIRC, there's a three-position sliding multi-contact switch that selects Band 1, Band 3, and UHF. A works colleague and I used a couple to make a pair of identical signal level meters. I'm sure I still have them somewhere, and only recently I thought I'd try to find them, and see if they were of any use for indicating the relative levels of the digital TV channels.