Signals: Field Cable, Alternatives and Metallic Circuits

[sjustice]

Hello all,

Technical questions here. Can someone explain to me the concept of forward signals equipment; specifically what is meant by lines of 'field cable' with exceptional alternative lines which might be 'semi-permanent'? Also, what is meant by 'metallic circuits', as opposed to...what?

I struggle with stuff that doesn't go 'bang' (by design).

Cheers,

Simon

[Terry_Reeves]

Simon

This book, a free download, should be able to answer most of your questions:

http://archive.org/details/signalserviceine00prie

TR

[WhiteStarLine]

Hi Simon,

Telegraph poles were classed as permanent or semi permanent and were not designed to be moved (or easily moved), hence placed where there was little chance of enemy shelling. They were placed on poles in high traffic rear areas to stop damage, particularly trucks and later, armoured vehicles. What were called 'airline' sections maintained them.

The correct name of the equipment was "Poles, telegraph, iron, semi-permanent," and they had on them "Brackets, insulator, tubular, iron pole, semi-permanent."

Metallic circuits were (usually) twisted pair circuits designed to minimise enemy overhearing telephone conversations through induction.

There were literally dozens of different types of line used and here is a very small extract:

[sjustice]

Thanks for the link, Terry.

Thanks, White. Can you just clarify why a twisted-pair would be termed 'metallic'? I presume standard cable was 'copper'...or is that the point? Do you know the specific difference between 'permanent' and 'semi-permanent'? I'd really like to nail this down a bit more. Sorry!

Cheers,

Simon

[Old Cove]

It seems from Terry's link - if I have understood correctly - that 'metallic circuit' was just being used to differentiate a two-wire circuit from one which used a single wire and ground or earth return. There is also an interesting article on the WW1 'Fullerphone' here: http://wftw.nl/fullerphone/fullerphone.html . It includes the sentence:

Hastily conducted experiments carried out within the Allied lines left no doubt about the cause of the leakage, and measures against eavesdropping were rapidly introduced by using metallic circuits (twisted pair of wires in stead of an earth return) within 3 miles from the front line.

Regards

Roger

[WhiteStarLine]

Yes, that is correct - a metallic circuit rather than single wire, earth return. I posted the first reply just before work and I was in a bit of a hurry.

'Permanent' refers to civilian infrastructure - French telegraph and telephone communication lines, poles, brackets etc. I would interpret the term 'semi-permanent' to mean an analogous system along the Line of Communication, out of observed artillery fire and built to roughly the same standard.

[sjustice]

Yes, that is correct - a metallic circuit rather than single wire, earth return. <snip> 'Permanent' refers to civilian infrastructure <snip>

It seems from Terry's link - if I have understood correctly - that 'metallic circuit' was just being used to differentiate a two-wire circuit from one which used a single wire and ground or earth return. <snip>

Regards

Roger

Thanks both.

Good stuff White, I actually get it now! No mean feat I assure you. Thanks to Terry for introducing me to 'Comic' lines, too. Priceless.

Cheers,

Simon

[Ron Clifton]

Hello Simon

Priestley's book is a cracking read, and reasonably clear to the non-specialist. I particularly liked the advice not to release male and female messenger pigeons at the same time as they tended not to go straight home - "pigeon nature being much like human nature in this respect" as he puts it!

Ron

[Terry_Reeves]

The source of Priestley's humorous comment almost certainly came from the pamphlet "Organisation of a Carrier Pigeon Service for the Armies in France. This is the relevant part, from page three:

"Paternal or material affection is supposed to be the chief cause of a pigeon's homing instinct, and it is an established fact that a pigeon returns in much better time if there is an egg or young in the nest.

When training, it is always advisable to fly male and female birds off the nest on alternate days. In case of necessity both birds may be taken, but as both take turns in hatching, feeding the young etc., the latter will be sacrificed."

This sheds a different light on Priestley's apparently off the cuff comment. If anybody has an interest in the pigeon service, I have a list of all the lofts, mobile and stationary, along with locations and dates.

TR

[adk46canada]

My non-technical understanding was that twisted pair was initially used to prevent interference when multiple lines were buried together. It was learned through bitter experience that wires needed to be buried and buried deeply to ensure communications, which required a great deal of effort. It made sense, then, to bury multiple lines in a single deep trench, however, without twisted pair there was too much interference when more than one line was used at the same time. Hence, the need for twisted pair.

Thank-you

Bill

[snapperxv]

Sorry to open another can of worms but does anyone have any pictures of the buried line marker posts which, if memory serves me right, are referred to as having carefully painted blue squares?

[centurion]

My non-technical understanding was that twisted pair was initially used to prevent interference when multiple lines were buried together. It was learned through bitter experience that wires needed to be buried and buried deeply to ensure communications, which required a great deal of effort. It made sense, then, to bury multiple lines in a single deep trench, however, without twisted pair there was too much interference when more than one line was used at the same time. Hence, the need for twisted pair.

Thank-you

Bill

Twisted pair were introduced by the French as they could not easily be tapped remotely by Moritz equipment as could single wire ground return systems. Unfortunately they omitted to inform the British about the German's abilities in this connection (the French had captured a German listening station) so Britain kept on using the single line ground return system which had the advantages of being easier to lay, lighter and easier to repair. The Germans could tap this from up to a mile away. Eventually a Canadian signaller discovered the problem and the Fuller phone system was adopted. Because this used a system of synchronisation between both ends of the line (called a buzz chopper) the signal could be scrambled. It was in any case much more difficult to tap and still used a single line. With the Fuller Phone even when broken by shell fire if the two broken ends of the line were reasonably close a signal still got through. However for really vitally important lines where voice was required and coding would take too long (or could give rise to dangerous misinterpretations) twisted pair was used. This applied to the switch boards connecting balloon observers to the telephone network

[Sturmey]

Thanks everyone, this is a fascinating topic.

I was wondering what your source was for your latest post, Centurion - the bit about the French capturing a German listening post. The idea the French were across this technology is amazing.

[WhiteStarLine]

Hi Sturmey,

Start at Chapter VI in the reference from post #2, specifically page 100 to page 108 or so. Some terrible examples of the waste of life from enemy overhearing telephone conversations.

[Sturmey]

Will do - many thanks