Feeder prior to 1950 or 1940

[Malcolm T]

Before those dates information is scant or impossible to find.
Before coax and baluns there was twin feeder for dipoles , but technology and feed impedance's changed and it seems twin feeder disappeared into the haze of history.
Has anyone done any work with 75 ohm twin lead or even lighting flex as a feeder or even remember some of the old boys having such set ups in their shack ?.

Many thanks

[G3VKM_Roger]

A dipole fed with a 75 Ohm balanced twin feeder will work fine with a modern radio having a 50 Ohm unbalanced output provided you have a suitable antenna matching unit (AMU).

The "Z-Match" AMU was/is a popular choice, you can build your own or look for a vintage AMU like a KW EzeMatch, KW-107 or KW-109. Do a Google search for Z Match ATU, there's lots of hits there.

You are not limited to 75 Ohm twin feeders, you can use 300, 450 and 600 Ohms and you can build your own feeders and a Z-Match to suit.

73

Roger/G3VKM

[Terry_VK5TM]

From the 1942 ARRL Handbook (there is about 4 pages in total on the subject):-

TRANSMISSION LINES
Requirements - A transmission line is used to transfer power, with a minimum of loss, from its source to the device in which the power is to ho usefully expended. At radio frequencies, where every wire carrying r.f. current tends to radiate energy in the form of electromagnetic waves, special design is necessary to minimize radiation and thus cause as much as possible of the power to be delivered to the receiving end of the line.
Radiation can be minimized by using a line in which the current is low, and by using two conductors carrying currents of equal magnitudes but opposite phase so that the fields about the conductors cancel each other. For good cancellation of radiation the two conductors should be parallel and quite close to each other.

Types - The most common form of transmission line consists of two parallel wires, maintained at a fixed spacing of two to six inches by insulating spacers or spreaders at suitable intervals (open-wire line). A second
type consists of rubber-insulated wires twisted together to form a flexible line without spacers (twisted-pair line). A third uses a wire inside and coaxial with a tubing outer conductor, separated from the outer conductor by insulating spacers or " beads" at regular intervals (coaxial or concentric line). A variation of this type uses solid rubber insulation between the inner and outer conductors, the latter usually being made of metal braid rather than solid tubing so that the line will be flexible. Still another type of line uses a single wire alone, without a second conductor (single-wire feeder) ; in this case radiation is minimized by keeping the line current low.

[G6Tanuki]

"Twin" feeder was available in the 40s and 50s from companies like Aerialite and BICC: I remember one version which had what amounted to a circular Polythene core with two slots along its length into which the conductors fitted, then a Polythene jacket over the outside.

It was horribly prone to water-ingress!

Most Brit WWII gear used coax - even then solid-polythene was ubiquitous as the dielectric, and the "Pye Plug" emerged as the connector-of-choice.

In the immediate post-WWII Band-I TV era there were a very few receivers sold with antenna-connections for twin-feeder. By 1950 the world moved to 75-Ohm coax and the "Belling-Lee" plug, and hasn't looked back.

In the amateur world, "Open Wire" feeder retains a strange fascination: personally I loathe the idea of bringing high-voltage/high-impedance feedlines into the shack [issues of how to bring them in through 18 inches of brickwork notwithstanding].

Coax to the feedpoint, then use a remotely-tuned impedance/reactance-matcher makes far more sense to me.

[Malcolm T]

Well thanks for the replys . No i was just curious as to anyone ever using such feeder methods today.
I have used 450 window line and then rolled my own open line at about 2 1/2" spacing and the difference was quite startling , with the doublet, but i have never actually been able to verify the real impedance of it set out as a length of open line on supports above the ground or for that matter cheap twin flex. Everything is geared today for coax ie 50 ohm
The Mini VNA is built for 50 ohm inputs isnt it ?.

[emeritus]

It seems that 80 Ohm twin feeder hung on for a few years after 1950. I have the 1952 and 1955 issues of the Belling-Lee newspapers that were given out at the annual Radio Shows. The 1952 issue lists both coax @1/7d a yard, and 80 Ohm twin feeder @ 7 1/2d a yard, together with connectors for coax, twin feeder, and screened twin feeder, and promotes twin feeder as an economic alternative to coax. They sold a coax to twin balun (L684 @17/6d) for use at the receiver end, and instructed you to remove the balun at the aerial end, this still being cheaper than a coax feed. BL must have still had faith in twin feeder, as this issue announced a new low cost 2 pin connector for twin feeder as an alternative to the larger and more expensive 3 flat pin connector.

In the 1955 edition the only 80 Ohm balanced feeder items are the 2 and 3 pin connectors, no balanced 80 Ohm cable being listed.

[Jon_G4MDC]

I used to have some 75 Ohm twin. It was oval shaped black plastic - I suppose polyethylene or such.

It was about 6mm wide and it had cores about 2mm diameter. One was plain hard drawn copper and the other was the same but dark brown enamelled for polarity indication.

I wish I still had some now. Can't find any of it.

[Radio1950]

I can remember using "figure 8" flex cable as transmission line myself for a 7 Mc/s folded dipole in about 1963, and with an 807 PA and Pi Coupler.
At the transmitter output, one feeder side connected to coax socket inner, and the other side just earthed!
I remember that we just used Belling Lee TV plugs and sockets.

Mismatches everywhere, losses high, but it worked, of sorts.

We didn't have SWR meters or RL bridges, just 6.3V light bulbs in series with TX output line.
The Pi Coupler helped a lot.

I always imagined Figure 8 cable to be about 150 ohms Zo at 5 Mc/s or so.
I must measure it!!
The loss of the PVC insulation at 10 Mc/s or so must be horrendous.

In Australia in the 1950's and 1960's, radio enthusiasts used a lot of 300 ohm TV feeder, some Figure 8, and WW2 Disposals type URM76 coax.
Disposals stores had large piles of rolls of URM76 or what we called "1/4 inch coax" on the floors.
Some "disposals" coax was preloved and in dirty condition, so it was relatively cheap, but cleaned up OK, and provided that you cut a yard or two off each end to get rid of the corroded braid.
.

[m0cemdave]

Originally Posted by Jon_G4MDC

I wish I still had some now. Can't find any of it.

I got some a few years ago at one of the larger rallies. I think it was from Westlake's stall.
It's feeding a fan dipole in my loft, works well.

[Richard675]

75 ohm twin was the feeder as supplied with the "anti tvi" trap dipoles from Richard G2DYM. The twin was a balanced feeder type connected to the dipole which was a balanced aerial of course. The transformation from balanced to unbalanced (balun) was done with a little unit at the transceiver end. A "proper" Z match with balanced output would do as an alternative.

Back in the day the idea of using a balanced transmission line would greatly reduce the chance of "tvi" and at the same time reduce pickup from TV timebases which used to plague the lower HF bands.......Happy days.

As yes, if needed flat twin lighting or speaker cable can be used, best used with a Z match. However, the characteristic impedance at HF might vary a bit from 75 ohms.


Interestingly, Richard told me that coaxial cables came to the fore during WW2.
Mainly in aircraft where the HF comms used an end fed aerial arrangement.

[Oldmadham]

Originally Posted by G6Tanuki

"Twin" feeder was available in the 40s and 50s from companies like Aerialite and BICC: I remember one version which had what amounted to a circular Polythene core with two slots along its length into which the conductors fitted, then a Polythene jacket over the outside.

It was horribly prone to water-ingress!

Most Brit WWII gear used coax - even then solid-polythene was ubiquitous as the dielectric, and the "Pye Plug" emerged as the connector-of-choice.

In the immediate post-WWII Band-I TV era there were a very few receivers sold with antenna-connections for twin-feeder. By 1950 the world moved to 75-Ohm coax and the "Belling-Lee" plug, and hasn't looked back.

In the amateur world, "Open Wire" feeder retains a strange fascination: personally I loathe the idea of bringing high-voltage/high-impedance feedlines into the shack [issues of how to bring them in through 18 inches of brickwork notwithstanding].

Coax to the feedpoint, then use a remotely-tuned impedance/reactance-matcher makes far more sense to me.

In Australia, Domestic TV antenna feeds were 300 Ohm ribbon, up to the early 1970s, when 75 ohm coax & "Belling Lee" connectors took over, much to the disgust of most techs, as they are horrible things.
The original Brit ones were pretty dire, but the later ones from the PRC were nightmarish.

The silly thing is that it wouldn't have been hard to make one with the same "business end", but with proper means of securing the coax cable braid & centre conductor.

I, for one, breathed a sigh of relief when "F" type connectors came along.

Transmitter feeders used in Broadcasting & HF comms in the '50s & '60s ranged over a wide range.
Some shipboard installations, just "end fed" the aerial.

There was a big feedthrough insulator in the Radio Room wall, with a beefy wire coming out of it, & heading off to where it was suspended from the mast.
The aerial was worked against a "counterpoise" consisting of the metal of the ship.

A lot of HF Comms & Broadcast stuff used 600 ohm open feeders -- real ones, using long lengths of heavy copper wire separated by air, except where they were supported by porcelain insulators at intervals short enough to prevent sagging, etc.

Others, mainly MF Broadcast sites,used 200 ohm versions of the same thing, & still others used "ersatz coax", in the form of "6 wire" unbalanced cables.

These used two very closely wires which were connected together at each set of supporting insulators as the "centre conductor", & four cables all connected together in the same way, as the "outer conductor."

I can't remember what the impedance was.

[Oldmadham]

Originally Posted by Radio1950

I can remember using "figure 8" flex cable as transmission line myself for a 7 Mc/s folded dipole in about 1963, and with an 807 PA and Pi Coupler.
At the transmitter output, one feeder side connected to coax socket inner, and the other side just earthed!
I remember that we just used Belling Lee TV plugs and sockets.

Mismatches everywhere, losses high, but it worked, of sorts.

We didn't have SWR meters or RL bridges, just 6.3V light bulbs in series with TX output line.
The Pi Coupler helped a lot.

I always imagined Figure 8 cable to be about 150 ohms Zo at 5 Mc/s or so.
I must measure it!!
The loss of the PVC insulation at 10 Mc/s or so must be horrendous.

In Australia in the 1950's and 1960's, radio enthusiasts used a lot of 300 ohm TV feeder, some Figure 8, and WW2 Disposals type URM76 coax.
Disposals stores had large piles of rolls of URM76 or what we called "1/4 inch coax" on the floors.
Some "disposals" coax was preloved and in dirty condition, so it was relatively cheap, but cleaned up OK, and provided that you cut a yard or two off each end to get rid of the corroded braid.
.

When I first worked at ABW2 TV transmitter site,in the late '60s, we had a lot of "UR67" cables still hanging around from the installation a
decade previously --------it was the only "UR" series cable I can remember seeing.
From memory, it was 50 ohm, but I'm not sure.

Previously, I worked in a Radio parts wholesaler between 1959 & early 1965. We sold "PT" series coax, PT1M, PT9M, PT21M, etc.
The 300 ohm ribbon from the same manufacturer was KA47.

I've never heard or read of this range since I left there, except for one fleeting reference to PT9M during a description of some complex scientific device from the 1950s.

[trh01uk]

Studies of the Auxiliary Units Signals section, which was a stay behind unit during WWII, shows that the radios they used, operating around 50MHz, were connected to a simple dipole antenna by some kind of balanced twin feeder. Remnants of this feeder have been dug out of the ground in a few places. It was probably about 80 ohm impedance, and I vaguely recall we had a type number for it - but no data has ever been found for it.

On the other hand, the RAF and British Army (probably Navy but I am hazy on that) were definitely using bucket loads of coax fairly early on in WWII. There is, for instance, the well known coax cable from the output of the WS19 both to its variometer and also to its B-set aerial. Both leads terminated by Pye coax plugs. Similarly the RAF used the same Pye plugs on oodles of radar, and radiolocation kit, like GEE, H2S, etc. Similarly some transmitters - WS12 and WS53 come to mind - had coax outputs to remote antenna tuning units.

So coax was definitely about by 1940 - and was probably used when money was no object.

Richard

[Radio Wrangler]

High power stuff used copper rods. Some were done as quads with a cross section of one wire at each point of a square held in place by spacers every so many feet. The wires were connected diagonally so they worked as a balanced pair. Air dielectric.

I've also seen 5 rod feeder, like the 5 pattern on dice. The signal on the centre wire and earth on the four around it as an unbalanced feeder.

I actually bring high voltage high impedance balanced open-line feeder into my house. The shack window is directly under my doublet, and the ATU is right by the window.

It avoids having to have a remote controlled ATU outside and having to weatherproof it, besides, it would have to either be in the driveway or on the roof. The antenna wire and the feeder wire are insulated, which is better in case anyone touches it, and it handles PME earthing regs.

I like open feeder where the impedance has to wander. I detest PL259s and I'm not at all keen on F connectors. I suppose I'm an N-type man, BNC at a pinch, but I aspire to APC-7 They're proper posh.

David

[Jon_G4MDC]

Get some 4.3-10s David. Thats N type size but a much better job made of the contact faces.
They don't empty your wallet as much as APC-7s but then you don't find them on much equipment apart from Cellular TXRXs.

[Malcolm T]

Thanks for the replys . Been searching and there,s scant info out there on pre 40 or 50s but i did find some people from across the pond doing some stuff and questions along the same line .
There is fascinating info on what the BC stations had and also the maratime ones as well as regards flat tops and feeding arrangements like the open line delta match . I think the RAF aerial riggers erected a lot of aerials of this arrangement . Was,nt there an installation up at North Weald Essex with numerous towers i remember seeing several times many years ago ?.
Any how getting a bit of topic here .
I think i will have a go at a 2 ele beam for the higher HF bands and feed it with some twin flex and see what the results are .
I found this in searching , the flat top beam
http://www.naapo.org/W8JK/W8JK.htm

[dave walsh]

Circa 1964, I used to bike round to a local amateur in Bury [G3TFN] He used open wire feeders and twisted pairs then, up to the aerials on his bungalow roof. He wasn't a stranger to coax though! I recall him showing me the resonance point on the open wires [six inches apart] with a neon. It didn't seem that uncommon to use the older style feeders that had once been the only options. He showed me the wire was just re-cycled cobbled together and the spacers home made from surplus perspex strips with a hole drilled at each end.

Conveniently, his place was next door to a Council Stores Depot in Whitefield and although retired, I think he was a sort of honourary caretaker [he'd been a Special constable at one time]. This is the chap who had a mint AR88 that I admired so much. The highlight was always when his wife served up great refreshments in the comfortable Radio Room within their property. Home made biscuits and Expresso Style milky coffee, very exotic then. The last time I saw him was in the mid seventies when he had moved near Bolton Street Station-now the famous ELR. Good times!

Dave W

[Panrock]

Here's some unbalanced feeder from 1937 - with aerial plug - from an EMI television.

More background on the plug is sought. Was there a Post Office association?

Steve

[winston_1]

Not only Australia, 300Ω twin feeder was common in continental Europe in the 60's.

It was also common in the US much later. Once cable TV became common US TV's often had F connectors for VHF and cable and balanced 300Ω connectors for UHF.

[TonyDuell]

Some US home microcomputers had a VHF modulator (where the UK version would have a UHF one to connect to our TV aerial sockets). They often came with a little switchbox to select between the TV aerial (OK, 'Antenna') and the computer output. This had a pair of screw terminals for the 300 feeder from the aerial, and a short length of such cable ending in a pair of spade lugs to go to the TV. The computer input was 75 Ohm on an RCA phono socket, there was a small balun transformer (wound on a ferrite bead IIRC) inside.

Such things were certainly used in the mid 1980s. I may have one somewhere still.