The BBC, PCM and NICAM for radio

Don Pearce wrote:

The reason I ask is that a friend's house has just had CATV installed
in place of an external antenna I fitted years ago. The difference I
notice is that on her new Sony TV's HD channels, my antenna signal is
comfortably in the green for strength, and 100% for quality, whereas
the CATV signal is just hovering at the top of the red for both.
You need to attenuate the signals by 6dB temporarily. If that affects
reception (I don't mean readings I mean reception) the levels are FAR
too low. Even a 10dB atten should have no effect.

I
suspect the noise figure of the CATV signal is good because a decent
size Yagi has line of sight to Crystal Palace about 10 miles away.
Big systems can deliver poor s/n ratios at the outlets even if the
aerial is OK. It only needs the levels to drop too far before
re-amplification, and after that you're amplifying a dirty old mess.

But
I think the system is new enough that she can reasonably ask for the
wick to be turned up a bit. I haven't measured her signal levels, but
what you say here gives me some idea of what they should be aiming
for.
Turning up the signal level in the streetbox will help the 'level'
reading but will only help the 'quality' reading if the poor quality is
caused by a poor signal to receiver noise ratio, as opposed to a poor
signal to system noise ratio.

That assumes that that the adjustment in the streetbox is be after any
amplification.

Bill

In article , Bill Wright
wrote:
Ian Jackson wrote:

I haven't checked, but I'm pretty sure that the analogue level spec on
large multi-channel cable TV systems was 63 to 75dBuV at the wall
socket (and less than 3dB between adjacent channels).
Yes that's right, but analogue needed a s/n ratio roughly 20dB better
than DTT, so in crude terms the delivered levels needed to be 20dB higher.

The old BBC advice was 1mV for BIV and 1.5mV for BV.

which was arrived at after testing a number of sets. Interestingly, tuner
became less sensitive with newer models.

--
From KT24

Using a RISC OS computer running v5.16

On Fri, 25 Nov 2011 17:44:53 +0000, Bill Wright
wrote:

Don Pearce wrote:

The reason I ask is that a friend's house has just had CATV installed
in place of an external antenna I fitted years ago. The difference I
notice is that on her new Sony TV's HD channels, my antenna signal is
comfortably in the green for strength, and 100% for quality, whereas
the CATV signal is just hovering at the top of the red for both.
You need to attenuate the signals by 6dB temporarily. If that affects
reception (I don't mean readings I mean reception) the levels are FAR
too low. Even a 10dB atten should have no effect.

I
suspect the noise figure of the CATV signal is good because a decent
size Yagi has line of sight to Crystal Palace about 10 miles away.
Big systems can deliver poor s/n ratios at the outlets even if the
aerial is OK. It only needs the levels to drop too far before
re-amplification, and after that you're amplifying a dirty old mess.

But
I think the system is new enough that she can reasonably ask for the
wick to be turned up a bit. I haven't measured her signal levels, but
what you say here gives me some idea of what they should be aiming
for.
Turning up the signal level in the streetbox will help the 'level'
reading but will only help the 'quality' reading if the poor quality is
caused by a poor signal to receiver noise ratio, as opposed to a poor
signal to system noise ratio.

That assumes that that the adjustment in the streetbox is be after any
amplification.

Bill

Thanks, yes I understand all this (I'm currently working for Global
Invacom designing their Ka band transceiver for rural broadband) - it
is just the street-level implementation details I was hazy on. I
suspect the installation is good - it is certainly very tidily done,
and the longest cable run is about 50 yards.

Your point with the attenuator is well made, and I didn't think of
trying that. I can bring home a switched one and see how many dBs I
can dial in before the errors start appearing.

d

On 25/11/2011 15:56, J G Miller wrote:
On Friday, November 25th, 2011, at 12:53:56h +0000, Bill Wright wrote:

I have a twenty quid Currys Essentials box on my bench that is
working on 26dBuV. There are occasional glitches. The box has a
duckfit if I turn the light on.

Sorry if this seems like an impertinent and irrelevant question,
but does it matter if the light is incandescent, fluorescent,
CFL, or LED?

Or is it the switch its-self?

I had a VHS tape that would stop playing if a light was turned on,
and it mattered not whether it was LED, GLS, CFL, gas or oil.
This isn't a joke, I'll see if you can solve the puzzle though.


--

Graham.

%Profound_observation%

On Friday, November 25th, 2011 at 18:14:33h +0000, Graham. wrote:

I had a VHS tape that would stop playing if a light was turned on

A particular VHS cassette, or do you mean a particular VHS cassette player?

Something to do with the infra red control on the machine?

On 25/11/2011 18:42, J G Miller wrote:
On Friday, November 25th, 2011 at 18:14:33h +0000, Graham. wrote:

I had a VHS tape that would stop playing if a light was turned on

A particular VHS cassette, or do you mean a particular VHS cassette player?

Something to do with the infra red control on the machine?

Assuming a particular deck, Optical sensor for the tape end ? Light was
leaking into the machine, and triggering the tape transport to stop ?

--
Mark
Please replace invalid and invalid with gmx and net to reply.

www.paras.org.uk

In article ,
Graham. wrote:
I had a VHS tape that would stop playing if a light was turned on,
and it mattered not whether it was LED, GLS, CFL, gas or oil.
This isn't a joke, I'll see if you can solve the puzzle though.

Optical tape present sensor.

--
*My dog can lick anyone

Dave Plowman London SW
To e-mail, change noise into sound.

On 24/11/2011 17:13, Jim Lesurf wrote:
Hi,

I've just put up a new page that people may find an interesting read, It
outlines the history of the use of PCM and NICAM by the BBC to distribute
their radio networks. You can find the page at

http://www.audiomisc.co.uk/BBC/PCMandNICAM/History.html

My thanks to the many excellent ex-BBC engineers who have helped and
advised.

Slainte,

Jim

Brings back memories. My first job when starting at Kingswood was
making and testing the pcb for, I think, the synchronising frame
generator for the prototype PCM equipment. It used a mix of ttl and
MECL logic chips, which caused problems, as ttl was +5v and mecl was -5.2v.

Phil

In article , Don Pearce
scribeth thus
On Fri, 25 Nov 2011 17:44:53 +0000, Bill Wright
wrote:

Don Pearce wrote:

The reason I ask is that a friend's house has just had CATV installed
in place of an external antenna I fitted years ago. The difference I
notice is that on her new Sony TV's HD channels, my antenna signal is
comfortably in the green for strength, and 100% for quality, whereas
the CATV signal is just hovering at the top of the red for both.
You need to attenuate the signals by 6dB temporarily. If that affects
reception (I don't mean readings I mean reception) the levels are FAR
too low. Even a 10dB atten should have no effect.

I
suspect the noise figure of the CATV signal is good because a decent
size Yagi has line of sight to Crystal Palace about 10 miles away.
Big systems can deliver poor s/n ratios at the outlets even if the
aerial is OK. It only needs the levels to drop too far before
re-amplification, and after that you're amplifying a dirty old mess.

But
I think the system is new enough that she can reasonably ask for the
wick to be turned up a bit. I haven't measured her signal levels, but
what you say here gives me some idea of what they should be aiming
for.
Turning up the signal level in the streetbox will help the 'level'
reading but will only help the 'quality' reading if the poor quality is
caused by a poor signal to receiver noise ratio, as opposed to a poor
signal to system noise ratio.

That assumes that that the adjustment in the streetbox is be after any
amplification.

Bill

Thanks, yes I understand all this (I'm currently working for Global
Invacom designing their Ka band transceiver for rural broadband)

Rural at that sort of frequency?..

What sort of ranges do they expect before the trees and other clutter
screw it up?..



--
Tony Sayer

"tony sayer" wrote in message
...

Thanks, yes I understand all this (I'm currently working for Global
Invacom designing their Ka band transceiver for rural broadband)

Rural at that sort of frequency?..

What sort of ranges do they expect before the trees and other clutter
screw it up?..

Several decades ago I was briefly part of a group working on what was called
the "pole-line route". This was going to work at around 40GHz, the idea
being that repeaters would be mounted on the top of motorway lighting poles.
But once the implication of rain attenuation calculations came to be
appreciated the project was quietly dropped.

David.