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View Full Version : The Great Invisible Rhombic Antenne


OFSO
13th Aug 2010, 10:51
Thinking back 55 years (or so) to what was then a completely different world, it's clear that we had some interesting adventures back in those far-off times, the sort of thing which is denied to present teenagers....

As Youths-in-Training with the GPO (Telecomms) in the village of E--- in the Midlands, myself and a few other young lads were techologically oriented and very bored. We were all fascinated with radio communications and while a few of us studied and became Radio Amateurs, a lot more didn't - and still went ahead and got 'on air' illegally. There was a lot of ex-military equipment on the market which could be bought quite cheaply and using transceivers such as the 38 Set (I wonder if anyone on PPRuNe actually used one of these in a combat situation ?) we'd set up comms nets which were buzzing many evenings.

One day we were discussing improving our transmission range (the 38 Set etc didn't have much range, and apart from one gifted amateur who built a beautiful 2 kilowatt transmitter - excellent wiring and sheet metal work, even if if did catch fire the first time he used it, we people using ex-military sets were limited to 'openings') so the only possibility open to us was improving our antennae.

Siitting outside on a rare Midlands evening when it wasn't raining, someone mentioned the huge rhombic antennae that Rommel set up in the north African desert pointing back at Berlin - each legs stretched a mile or so, maybe more. We sat looking down the street, and I don't know which of us lifted his eyes to the telephone poles that were everywhere, but the idea caught on. The first thing to procure was copper wire, lots of it, and I suspect it was bought at Proops of Oxford St where all sorts of amazing things could be founds: aircraft instruments, mechanical computing devices, pipes and hoses and gas masks, etc. Anyway once we had the wire it was a matter of borrowing someone's ladder and stringing it up on the existing telephone poles of our little industrial village. In those days there were few people about after 10 p.m. and no cars, so it didn't take long to set up a rhombic antenna at roof-top level, stretching over several streets, and pointing west at the USA.

The results were quite good, although whether due to the rhombic design I don't know. In fact one early morning 'someone' attached a transmitter to it thru a balun and claimed to have been heard in Florida - although for obvious reasons it was never tried again.

The Great Invisible Rhombic Antenne lasted about three weeks. It was never discovered as such, but one evening the bus route into Leicester was disrupted by a burst water main, and the route changed: sadly the familiar red double-decker came down the road where the rhombic antenna had been strung a bit too low, and that was the end of it.

Shortly afterwards I moved to London and from there to Germany, lost contact with the others, and never heard the end to the story. Although there was a postscript. Someone living in E------ told me much later that one evening the street lighting was brightening and dimming and flickering in a strange way: after a bit he figured it was probably morse code and that (name deleted) had built his super transmitter, bypassed his parents fuse box, and was feeding it from the street lighting supply. Ah well: happy days.


Anyone else got any similar reminiscences ?

radeng
13th Aug 2010, 11:06
OFSO

Some of the people from the Vintage and Military Amateur Radio Society still use 38 sets! As well as 19 sets, R1155/T1154 etc

VMARS-The Vintage and Military Amateur Radio Society (http://www.vmars.org.uk)

But the rhombic would have been too low to be really effective

Gainesy
13th Aug 2010, 11:53
Very basic question. Does wire used as an aerial (radio) need to be bare or can you use wire with insulation on it?
Kid up the road wants to run an aerial from his tree house using garden wire which is the lightweight stuff used to tie in plants and has green insulation. Would it work as is or would he need to strip it?

green granite
13th Aug 2010, 12:43
It'll work quite happily with insulation on it.

radeng
13th Aug 2010, 12:47
If it's a critical length that's needed, insulation does have an effect. Garden wire is generally iron or steel wire, so it's not as efficient because of the resistance. I doubt very much if the effect will be noticeable enough to matter.

green granite
13th Aug 2010, 13:00
Never progressed to the 38 set, my time in the signals section of the cadet force we used these for mobile use
18 set
http://i68.photobucket.com/albums/i11/orangeherald/18set.jpg

And this in the base "office"

19 set
http://i68.photobucket.com/albums/i11/orangeherald/19set.jpg

tony draper
13th Aug 2010, 13:11
One is a tad puzzled as to why go to the bother of obtaining yer own copper wire? telegraph poles are generally festooned with miles of the stuff,just needed a few disconections and tape joints and bobs yer uncle.
:rolleyes:
I have strung cable along pole lines only to discover a couple of ragmen with their own ladder following me and unstringing it,one of the few occasion when cable thieves were caught on the job as it were,the Copper(two legged variety) would not allow us to give em a good kicking.
:uhoh:

G-CPTN
13th Aug 2010, 13:30
Not a radio anecdote, but a telephone one.
During time at a campus university, a group of friends found themselves with rooms at opposite ends of the campus. This meant that communication (this being long before the advent of the mobile 'phone - and none of the students had proper GPO telephones in their rooms) was by Shanks's pony (http://wiki.answers.com/Q/What_is_shanks%27_pony) whenever liaisons were being planned or academic work problems needed discussion.
To counter this it was decided that a telephone system was needed. Experiments with inductive loops around the GPO wires that served the rooms of tutors indeed picked up the conversations, but the complexities of constructing an independent signalling system (and the risk of being detected should the legal user pick up the instrument during furtive use of the line) ruled out that plan. Instead, field telephone wire was acquired from the CCF stores and, over the span of a few nights, this was strung across rooftops and from spire to spire of this ancient establishment.
The system was a complete success and for a number of weeks it operated as intended, saving much legwork whenever messages needed to be passed.

Then! the College decided to restore some decaying stonework and the masons moved in and started to dissemble some of the spires that served as supports for the wiring. Much breath was held should investigation of the destination of this wire be undertaken, and it was accepted that the connection would be severed, however the contractors erected temporary supports for the wiring and, having finished their restoration, replaced the wiring without disturbing the connections.

This wiring was never removed (by the students), and it has been pondered whether it is still there some 45 years later . . .

sitigeltfel
13th Aug 2010, 13:42
When I was a teen I had a pal who was into ham radio and general electrickery stuff. He wrote off to some of the big companies such as Marconi, GEC, Cable & Wireless etc. asking if they has any bits and pieces spare that he could use as he was an impoverished student.

Well, he ended up with shed loads of stuff and it drove his mum to banish it all to a lock up garage. There must have been a couple of thronomeisters in amongst it all, I wonder if he put them to good use.

Captain Stable
13th Aug 2010, 13:56
We used these for mobile comms:-

http://www.wftw.nl/wireless/ws88.jpg

These for semi-mobile:-

http://www.vmars.org.uk/Image15.gif

And these for base station, and these were also my first dive into Ham Radio - as G3-WUC/A:-

http://www.ab4oj.com/1st/ws62.jpg

Gainesy
13th Aug 2010, 14:46
Thanks chaps.
I think he's more looking forward to stringing it up (bow and arrow over a couple of trees) rather than the rx results, still, he's not sat on his bum playing computer games.

OFSO
13th Aug 2010, 14:51
when cable thieves were caught on the job

A slight Darwinian drift, but two weeks ago thieves here who had been stealing telephone cables made a slight error and cut into a three-phase mains cable (easily done if you are an idiot, but phone ran down one side of road and power down the other). Put paid to their practices. Still, they were South Americans......

Back to thread: since I raised hell with Telefonica two months ago, our urbanisation's had a lot of work done, even to the extent of cutting down almost new sections and putting up new ones - suspension wire and two pairs in one plastic housing. The Telefonica guys just leave the 'old' cable lying on the roadside. Naturally I've collected it (a) to make the place tidy and (b) to use it some day myself. I've been thinking of superimposing my own phone network on the Telefonica poles - they'd never notice.

Note to person wanting to string aerial to nearby tree: use a pulley at the tree end, run the wire over it, hang weight on end. Otherwise when wind blows, tree moves, aerial ripped out of house. Also - and this is deadly serious - think about correct grounding. Or when the thunder booms and the lightning strikes, you might be in very bad trouble and appear in these pages as a Darwin Award.

G-CPTN
13th Aug 2010, 15:14
BBC News - Leeds cable thief is jailed for two years (http://www.bbc.co.uk/news/uk-england-leeds-10950908)

Jail for prolific cable thief with drug debt who caused rail chaos - Yorkshire Post (http://www.yorkshirepost.co.uk/news/Jail-for-prolific-cable-thief.6473485.jp)

green granite
13th Aug 2010, 15:37
I've been thinking of superimposing my own phone network on the Telefonica poles - they'd never notice.

Bit like this OFSO?

http://i68.photobucket.com/albums/i11/orangeherald/wires.jpg

radeng
13th Aug 2010, 15:38
Thread drift vaguely towards aviation...


After Decca installed the first ILS at Buenos Aires - in the 1960s - the work had been noted by the locals. Two days after the handover, an alarm went off at about 0400 - the outer marker beacon transmitter had gone off the air.

The technician arrived to find the the thieves had used a bull dozer or similar to pull the armoured mains cable out of the ground - best part of half a mile of it - and disappeared with it!

hellsbrink
13th Aug 2010, 16:38
Ahh, self made antennae. Brings back memories of when I was younger (13).

Parents got me a UK legal CB radio, and a legal antenna (1.5m, base loaded). Of course, that was never going to last and soon I started faffing around with other manufactured antennae but the results were never quite satisfactory. So, one day after being given a book with all sorts of formulae and designs for antennae, the inevitable happened after I managed to get my hands on the materials. First attempt was a 1/4 wave dipole, vertical, with 4' of the ground side dug into the ground and the rest, a total height of around 15' lashed to some plastic trunking lid tied to a metal pole. Because of the way everything sat I got a great signal in a southerly direction, and could get a signal all the way to England with the right "skip" conditions, which is no mean feat with a 27 Mhz 4W FM transmitter. Of course, that wasn't enough, so plans soon arose to make the antenna "bigger" by using loading coils. After some experiments I figured out that a centre loading coil had the best results, so the equivalent of a half-wave was created with some real success as people over 5 miles away were getting a signal strength from me like they would if I was within a mile of them and being able to "skip" a signal into France. Success!!

That, of course, did not last long. Next came a helically wound one, equivalent to 1 1/2 wave. This worked too well, and had to be scrapped after it was found that I would interfere with half the TV's in the street every time I transmitted. It had to come down. Of course, the next projects were a multi-element antenna (like a TV aerial) and a parabolic but neither came to fruition due to complications like finding something suitable to use as a dish.......

Then along came a serious interest in beer, women and partying so more experiments were pushed away into the deep background. Must say I had fun times in them days, especially when your own home made "thing" worked better than many manufactured antennae!

OFSO
13th Aug 2010, 20:16
Yes green granite, but around here the junction box lids are always open or missing. And the wires are 'terminated' by being twisted together by hand.

Golly, when I think of how much time as an apprentice I spend using that winding tool to get two copper wires (4lb per something or other) to bite into each other....my instructors from Stone would take one look at the average Telefonica job and go off and shoot themselves.