EMI TV end fed wire antenna.

[G6Tanuki]

I have vague memories of a TV antenna promoted by EMI in the early days of broadcast TV - it was a long-wire (meaning several wavelengths long) horizontal wire which you were meant to arrange so that it was radially oriented as a ' spoke on a wheel ' with the transmitter at the centre of the hub.

I guess it was a sort of Beveridge antenna..

But was it terminated by a proper resistance and quarter wave end?! And how effective would such an antenna be?!

[peter_scott]

If it's this one it looks as if it separates the radio and television aerials.

Peter

[Graham G3ZVT]

The transmitting aerial at Alexandra Palace consisted wire elements attached to insulators.
Described as eight pairs of push-pull end-fed dipoles with reflectors.

Pg195
https://www.bbceng.info/additions/20...V%20System.pdf

Oddly for a document that describes the station in minuet detail, there is no diagram of the aerial.

[peter_scott]

http://marconiintelevision.pbworks.c...a%20Palace.pdf

[emeritus]

The Ally Pally transmitter aerial was the subject of its own illustrated booklet, which possibly explains its absence from the posted document describing the station. I posted a scan of the aerial booklet on this forum some years ago but don't recall which thread. I couldn't find it just now using the forum search, so I guess it's gone. I do still have the original booklet, and its scan, but the scan is backed up somewhere on my old computer and the booklet is in a box somewhere in the shed.

[wd40addict]

https://www.vintage-radio.net/forum/...7&postcount=10

[G6Tanuki]

Some interesting antennas there, but the one I am thinking of was a receiving antenna for domestic use... A long wire, horizontal, fed using coax cable. Assuming that you had a long enough garden you arranged for the wire to have the far end pointing towards the transmitter...

[murphyv310]

End fed Antennas are high impedance so a very poor match to 75 ohm coax. A balun would need to be constructed around 47:1 of course that's dependent on the length of the long wire.

[peter_scott]

Originally Posted by G6Tanuki

Some interesting antennas there, but the one I am thinking of was a receiving antenna for domestic use... A long wire, horizontal, fed using coax cable. Assuming that you had a long enough garden you arranged for the wire to have the far end pointing towards the transmitter...

Are you sure it's not this one that you are thinking about. One of the three lengths is 5'.

Then in 1950 they produced a simple indoor one that might be the 5' section without the radio aerial.

Peter

[AdrianH]

I have the book 'Television Principles and Practice' by F.J. Camm dated 1955 and under the aerials section is a 'Tilted wire aerial' described as A long wire of highly directional properties which requires space for erection. Not a lot of details about it.

Adrian

[Panrock]

On 8th February 2007, Ray Cooper wrote, in the thread "The earliest television aerials":

"The 'tilted wire' aerial - in effect, a vertical half-rhombic - could give very good results IF you had enough real-estate to erect one, and IF you could point it in the right direction. Those conditions satisfied, they could be a good candidate for home-construction. "

I have a picture of this arrangement somewhere, taken from an old magazine, but I'm dmned now if I can find it!

What sort of gain would this type of aerial have had on Ch.1?

Steve

[AdrianH]

A quick search on wireless history site. and there is an article in Wireless world. 1939 31st August page 206.

Adrian

[G6Tanuki]

Originally Posted by AdrianH

A quick search on wireless history site. and there is an article in Wireless world. 1939 31st August page 206.

Adrian

That's closer to what In recall, but what I remember was a horizontal wire.

If anything it was like the 'windom' or 'off-centre-fed' antenna; the memory's not 100% but if you were to put up a wire that was quite a few wavelengths long, then break it 1/4-wavelength from one end and attach your feeder across the break - looking at details of long-wire antennas in the Moxon book, the feedpoint woiuld be somewhere between 50 and 100 Ohms impedance, and the polar diagram looks distinctly gainy along the axis of the wire [unlike a classic dipole where the gain is greatest at 90 degrees to the axis].

[Graham G3ZVT]

The bit I have difficulty with is "The far end of the wire pointing towards the TX". Wouldn't that be a null point?

[emeritus]

Here's a description of how to make a tilted wire TV loft aerial from Odhams "Radio Television and Electrical Repairs" book, 3rd edition, 1956. It does say that the aerial should slope towards the transmitter, and each half should measure 5' 4 1/2", making it about 10' 9" long overall, and specified twin feeder. By the time the book was published, Belling- Lee for one had discontinued 75 Ohm twin feeder.

Because the aerial slopes, the end-on null points dowards towards the ground, not towards the transmitter. The missing introductory paragraph on the previous page, which I haven't posted, says:

"Fairly close to the transmitter, and where there is little interference, no reflector is needed and a " (continues with page 296 "cheap aerial ....).

[Andrew2]

Originally Posted by rambo1152

The bit I have difficulty with is "The far end of the wire pointing towards the TX". Wouldn't that be a null point?

If the wire was several wavelengths long, it would become more 'end fire' than 'broadside', a la Beverage (although without the end termination). I doubt most ordinary people would have room for it though!

[G6Tanuki]

Originally Posted by Andrew2

If the wire was several wavelengths long, it would become more 'end fire' than 'broadside', a la Beverage (although without the end termination). I doubt most ordinary people would have room for it though!

Yes, it would be operating as an end-fire antenna. The Moxon book has some polar diagrams, for antennas up to 2-lambda long and some longer; there's even acknowledgement that the directly end-on null is probably a lot less in practice than the equations would predict.

I've been looking around at places like http://www.earlytelevision.org/ which has some good examples of pre-and post-WWII TV antennas, and looking at the 1930s records of amateur experimentatioin on the then-permitted 56/MC/s band; several operators in the famous Snowdon trials were using end-fed antennas but I haven't been able to fond evidence of my V Long-Wire.

[An incidental question: all the photos on earlytelevision.org show the US VHF antennas to be horizontally-polarised, but the UK ones are vertically-polarised. Why did the UK adopt vertical polarisation]

[peter_scott]

Quoting from:here:

Peter

[G6Tanuki]

Originally Posted by peter_scott

Quoting from:here:

Peter

Fascinating... must admit, my experience on 50, 70 and 144MHz has been that horizontally-polarised signals give better distance-covering ability. Vertical polarisation makes sense for mobile [handheld walkie-talkie and whip-antenna-on-a-vehicle, working to a vertically-polarised repeater or base-station] - if only because omnidirectional horizontally-polarised antennas are practically difficult to engineer for handheld or vehicle applications.

Horizontal polarisation was used for UK Band-II FM broadcasting.... though from the 1870s there was a move towards slant polarisation so mobile/portable reception was better.

[Panrock]

Originally Posted by Panrock

What sort of gain would this type of aerial have had on Ch.1?

From the Wireless world article, this looks to be the same as an 'H'. Where it excels, however, is in its strongly directional characteristic. In a suitable location it could be much less prone to motor car interference.

Steve