Re: How good were 1950's/1960's Band 1 TV receivers?

In article <1185878196.504809.207380@xxxxxxxxxxxxxxxxxxxxxxxxxxx>, Mark
Carver <markcarver@xxxxxxxxxx> writes
On Jul 31, 11:19 am, Roderick Stewart
<escapet...@xxxxxxxxxxxxxxxxxxxxxx> wrote:
In article <memo.20070730230534.38...@xxxxxxxxxxxxxxxxx>, Paul Cummins
wrote:

Also, the signal would be far more watchable, since signal errors would
only affect the luminance - making it less defined in shade only, so
intereference would not be so noticeable.

Not sure that I follow that argument. I see someone has already made the
point about ignition sparlkies, but there's also the matter of AGC. With
positive modulation, proper AGC not related to picture content is more
complicated to implement, and in the days of thermionic valves it was
common to economise on components in the interests of costs. Thus, RF AGC
would depend on the average picture brightness, and combined with the
effects of capacitor-coupled video amplifiers, the dynamics of the
pictures displayed in most homes would have been nothing like what was
seen in the studios.

I can't remember seeing black level clamping on many b/w sets, 625 or
405, though I'm a bit too young to remember 405 lines that well.


The old Baird chassis had that as well as some Bush sets which made a
great fuss of it, but there were very few sets that did...

The other point about impulse interference being less visible on
negative modulation pictures, well is it in practice ? Surely
overshoot within the receiver's circuity would give any black dot a
nice white edge ?

Take into account as well the advent of UHF where impulse ignition
interference wasn't so much of a problem and over time the suppression
levels on cars improved...
--
Tony Sayer
.

Relevant Pages

  • Re: How good were 1950s/1960s Band 1 TV receivers?
    ... but there's also the matter of AGC. ... proper AGC not related to picture content is more ... I can't remember seeing black level clamping on many b/w sets, ... negative modulation pictures, ...
    (uk.tech.broadcast)
  • Re: How good were 1950s/1960s Band 1 TV receivers?
    ... only affect the luminance - making it less defined in shade only, ... intereference would not be so noticeable. ... but there's also the matter of AGC. ... proper AGC not related to picture content is more ...
    (uk.tech.broadcast)
  • Re: earth loop problem
    ... AGC to the RF and IF amplifiers by obtained simply by low-pass filtering ... level constant.. ... such trivial points as a correctly presented picture, or decent sound. ...
    (uk.rec.audio)