DIYbanter - View Single Post - Audio Precision System One Dual Domani Measuirement Systems

Terry Casey

In article ,
says...

In message ,
Terry Casey writes
In article ,
says...

Other western European countries[1] used system B in a 7MHz channel
width and system G in an 8MHz channel at UHF.

To use the same channels we would have needed to devise a system X with
a truncated vestigial side-band to fit our 6MHz sound-vision spacing
into 7MHz - in reality, I don't think it would have fitted!

Of course, both the British and the Irish could have simply adopted the
European systems B and G (5.5MHz sound-vision - plus the horrendous
group delay pre-correction curve).

As the UHF bands had been engineered by international agreement for 8MHz
channels to accommodate all European 625 line systems (with the vision
frequency being common to all of them), it made sense to make better use
of the bandwidth available - in fact, as we were starting from scratch,
I've often wondered why we didn't adopt the eastern European OIRT
standard with its 6MHz vision bandwidth.

As for group delay, I suppose it made sense to pre-correct the
transmission to suit the average receiver group delay response. Were the
system I parameters, without group delay correction, determined in the
belief that UK manufacturers were so much better at designing IF strips
than their continental counterparts? ;-)

Group delay was something I never thought about - until a rude awakening
doing early experimental work on Teletext - but the introduction of SAW
filters resolved the problem ...

If I remember correctly, the only
difference between systems B and G is the 7 vs 8 MHz channel spacing.
Even the VSBs are the same (0.75MHz).

Yes, but don't forget the Belgian system H with 1.25MHz vsb ...

In practice, if we had decided to carry on using VHF for 625 line
broadcasting, I think we would have harmonised with the Irish 8MHz
channel plan - not least because of the proximity of NI transmitters to
those in the republic.

Again, IIRC, the RoI VHF 625-line channels were the same frequencies as
the 'lettered' 625-line channels already used on many VHF cable TV
systems.

Chicken and egg situation? RTE was broadcasting using VHF 625-line
channels at least two years before BBC2 came along. I think you meant:
many VHF cable TV systems used the 'lettered' 625-line channels already
used by RTE ...

Continental systems, of course, used the CCIR broadcast channels, as
well as filling up the gaps in between ...

--

Terry