The London Television Cable

[Tractorfan]

Hi,
With the upcoming Coronation of King Charles III, a thought came into my head that I'd read something about a televised Coronation long before that of Queen Elizabeth II.
Thus, I dug out a fascinating old book that belonged to my late father. It was entitled: 'How It Works And How It's Done' published by Odhams in the late 30s.
In the chapter: 'The Magic Eye; How We See By Television' is mentioned the television coverage of the 1937 Coronation of King George VI using Emitron cameras.
A cable was installed around London with plug points at various places to connect the cameras.
So, I was wondering if this cable still exists and if the connection points can still be found. I assume they were under little cast iron covers hither and yon.
After the Coronation, it was used for the Lord Mayor's Show, the Armistice Day Cenotaph ceremony, and other events.
Cheers, Pete.

[turretslug]

LoCo, or London Co-axial. It was used for many years subsequently, but was prone to co-lateral damage.... by diggers etc. It was supposed to be pressurised to a few PSI with dry nitrogen, but damage was all too frequently betrayed by zero pressure reading. Even when working, video often had to be sent at high level with considerable pre-emphasis for satisfactory results (1980s, 625 PAL), regarded as a back-up for microwave links by then if it worked at all. No doubt there are still dusty cabinets dotted around with their linking loops, Schrader valves and Bourdon guages.

[nsykes1]

Good page about the LoCo is here:
http://www.bostonmanor.plus.com/exbhcomms/LOCO.html

Neil

[Roger Ramjet]

This is fascinating to know ....

1. Was it the GPO who installed & maintained the cable.

2. Was the cable installed in a dedicated duct or with other telephone ? cables.

Rog

[turretslug]

I'm reminded now of the "LoCo drivers", essentially a DC-coupled RF PA that sent high-level video into the run, one thing that sticks in my mind is the plus/minus 23V rails, I think this was as high as the designer dared push the "capstan" package devices! As the artilleryman in Good Morning Vietnam said, "I don't care what you play so long as it's L-O-U-D"..... Someone here will doubtless know the equipment code.

[gingpeakin]

And those amps were full of berryllium dioxide. +23dB comes to mind which is a bit crazy. You could also see microphonics from the underground. We only ever used it as an emergency backup in the early 80s.

Ging

[beamcurrent]

Yes the AM7/512 Line Sending Amplifier. I often thought those would make a plausibly good QRP transmitter for 80 meters?

I remember it from the mid 1980s and the "U" link was PL259 connectors? not the most reliable of connectors. Could you send both ways round the loop?

[PaulM]

I have a piece of something similar - same sort of GPO technology and kit, but from the 'ITV side' of things. It came from Teddington Studios (former ABC) and had probably been there since 1958, or perhaps longer. Attached is a picture of it. It's just the pressurising part, but you can see two MUSAs where the coaxial connection was made. I was told that it went all the way back to the GPO Tower. In due course, it will now go up to our Broadcast Engineering Museum. Not sure which section to display it in!


Best regards,

Paul M
BECG www.becg.tv

[Station X]

I don't think those are MUSA connectors, they're just pipe fittings.

This is part of GPO/BT "Equipment Cable Pressurisation". The two triangular type handle wheels on the manifold control air flow from a compressor and desiccator into the cables.

The pressure gauge has a variable alarm setting to raise an alarm in case of pressure drop. The contacts are wired to the tag strip.

[PaulM]

OK, that was just the 'file picture', and I've now had a look at the actual item.
The ones facing look like MUSA in the picture and they're the right size, but in reality they're actually Schrader valves (think car tyre). I hadn't physically looked at it for quite a while. Still a little piece of history.

There's holes and a space for something on the right hand side - I'd always assumed a launch amplifier? This was all that was left of the system at Teddington.

Best regards,

Paul M

BECG
www.becg.tv

[Station X]

I don't think anything other than cable pressurisation equipment would have been fitted to this panel. It's possible that flow gauges (balls in a glass tube) were fitted on the RHS of the panel.

The Schrader valves were used to connect a compressed air cylinder with regulator should the compressor fail.

You can tell this is an early panel as on later ones the air tubing was covered in white plastic.

[Amtec123]

Nice to see a bit of old Tedder's survives.
Having joined Thames Teddington as an engineer in 1972, my first job was in Central Apparatus Room. This was sited next to the Master Control Room, we were responsable for both MCR plus most of the other Studio equipment. However a strict line was drawn once signals left, or prior to entering MCR's DA's, that was Mr Postie's (GPO)responsibility. The room containing their equipment was locked and out of bounds to us. Any faults were delt with by their engineers. Most were very friendly, so we got chatting to them whilst the room was open. There were 4 video circuits from the BT Tower TFS-V1 & V3 outgoing, and TFS-V2 & V4 incoming (1 of which was reversable). Anyway back to the gas pressure device, one set was for the main in /out circuits. However another set was for a couple of circuits which went to another Thames site above a furniture store in Teddington High St. I'm not sure what it was originally used for by ABC, but when I was there it only carried the "in house" TDUK system. There was also a GPO rack of equipment painted 'PO yellow' containing line drivers, EQ amps, and fault alarm systems.
Fond memories
Les

[ScottBouch]

Fascinating information there!

I love discovering about unknown/underground networks like this.. (and tunnels and bunkers!)

Thanks..

[CambridgeWorks]

Post 8, the 2 valve handles are the same as I had on a R12 refrigerant cylinder over 50 years ago, mine were marked RCL, same as the gauge. The brass fittings are standard flare types of the earlier style and the copper pipe looks to be standard 1/4" refrigeration type as well.
I think RCL was Refrigeration Components Ltd, but could be wrong.
However, refrigeration gauges were usually just compound, 30" vacuum to maybe 100psi and HP, 0 to say 200psi.
That must have been a special by RCL. However GPO etc would be a big consumer.
Graham, was the white covered air tubing aluminium, around 10mm o.d?
If so, I still have about 30M left in a coil, we use it for hoops to hold fleece over plants!
Were the mains powered small compressors just a motor with a squareish compressor on one end that was about 5" square? Maybe 20psi max? Overall maybe 12" long.
I used to see lots of those, ex bt and might even have a valve plate repair kit.....somewhere.....
Rob