Antenna identification

[84KB11]

Can anyone identify the below antenna?

 

Details on it read:

 

W8

Antenna

FV953926

NSN: 5985-99-209-6772

 

The mount looks like a standard larkspur whip antenna mount, modified to take the larger diameter tube. Connector on the coax is std PL259 type.

[Redcap]

It looks remarkably like a three-element folded yagi of some sort, but I've never seen anything like it before in Army use...

 

Looking at the size of it (comparison based on the card tag on the string), I would have said it's a UHF antenna, but the PL-style plug tends to argue for a low VHF or even HF band. This is confusing. Granted this is gonna be a pie in the sky wish, but is there any chance you can stick the thing on an Antenna Analyser, to gauge the operating bandwidth of it?

[84KB11]

Hi Roger,

 

I would agree that it is likely to be a folded Yagi of some sort. It has the feel of being made by J-Beam (who did do so some stuff for the military).

I would guess it would be somewhere between 300 and 400mHz, but will try and get it onto an analyser at some point to confirm this.

 

I was thinking it had a Ptarmigan/Triffid type look about it, but never seen anything like it before to confirm this.

 

Anyone else out there have any ideas?

[AlienFTM]

We certainly never used anything like that, simply because it was appropriate for our role, but we shared a barracks with a Task force (Brigade) HQ and Signals Troop and I do remember once being in conversation with a Scaleyback sometime either side of 1980 who mentioned using Yagis. This being a Yagi, I thought of TFE HQ & Signals Troop when I saw the pic.

[Redcap]

hmm... may well be related to Ptarmigan or Triffid, they're both point to point systems, but I was under the impression that those used masthead dishes, rather than loose directional antennas. Be interesting to get the results of the analysis, at the very least you'll have a better idea of how you might be able to use it

[AlienFTM]

hmm... may well be related to Ptarmigan or Triffid, they're both point to point systems, but I was under the impression that those used masthead dishes, rather than loose directional antennas. Be interesting to get the results of the analysis, at the very least you'll have a better idea of how you might be able to use it

 

Ptarmigan. There's a name from the past, and thinking about it, in all probability from HQ TFE. It threatens to come together.

 

But I wouldn't bet my shirt on it.

[fv1609]

Hi Roger,

 

I would agree that it is likely to be a folded Yagi of some sort. It has the feel of being made by J-Beam (who did do so some stuff for the military).

I would guess it would be somewhere between 300 and 400mHz, but will try and get it onto an analyser at some point to confirm this.

 

I was thinking it had a Ptarmigan/Triffid type look about it, but never seen anything like it before to confirm this.

 

Anyone else out there have any ideas?

 

It was made by Thorn EMI.

 

If you measure the length of the folded dipole, allowing for the velocity factor of the metal, it will be a half wavelength & give you the frequency.

 

(By length I mean the length that it is as you look at it, not the total length. "Folding" the dipole was just a matching ploy by altering the impedance, although goodness knows it is pretty poorly matched with the dipole being balanced going, it seems straight, into the unbalanced coax)

Edited September 11, 2008 by fv1620

[antarmike]

Looks like an attempt to get channel 5 to me....

[84KB11]

Finally got round to measuring the elements on the antenna.

Hope this makes a bit more sense of what this may have been for.

 

In case it is difficult to read the measurements, from left to right they are:

30cm, 8cm, 33cm and 43cm.

[fv1609]

I've assumed the diameter of the driven element is 1/4 inch. So it puts its centre operating frequency as 220 MHz.

 

PS I was just wondering whether that 33cm measurement is more like 32.3 cm? That would then put it at the old lower end of the mil UHF band at 225 MHz. Although that lower end has now shrunk up to 230 MHz.

 

So your little yagi should give you a nice DAB signal :-D

 

http://www.wibble.co.uk/links/ukspectrum/spectrum.html

Edited September 21, 2008 by fv1620

[Redcap]

heh, I'm betting on the latter - I've never yet seen a telly in military use to have a poor signal:evil::whistle::rofl:

[fv1609]

Sorry I made a complete mess of that.

 

Whilst converting it into proper inches I mistakenly took the measurement as a 1/4 wave but in fact it was a 1/2 wave. So the frequency is double ie 440 Mhz.

 

Just looking at it didn't seem right. Not very good when when you consider I built my first transmitter for that band in 1964. But in those days it was a bigger bit of spectrum 420-450 Mc/s. (yes in those days proper megacycles per second, a measurement that means what it says)

[Redcap]

hmm... still feasible - UK Ham allocation at 70cm is secondary, after all

[84KB11]

Thanks Clive,

 

440Mhz would put it in the Ptarmigan/Triffid type frequency range, so this is still a possible use for it.

Would be nice to know what it was actually for, and what vehicle it was fitted to.

 

Shame it was not in the DAB band range, would have looked different on the Land Rover!

 

Will have to take it to a few shows and see if anyone else recognises it.

[fv1609]

I think as you said earlier it was made by Jaybeam. I was tempted to buy one 25 years ago just to pinch the folded dipole & connector block to use on 70cm. The whole thing was more rigid & more waterproof than the stuff they produced for the amateur market & I was just going to transplant the dipole onto the amateur yagi. But I have never yet found out the application for the original yagi.

[schliesser92]

Triffid.

 

The yagi array was used for the lower frequency ranges 8300-500 MHz) for brigade/task force links. The dishes referred to were for higher frequencies and used in the div/corps links. This meant that these vehicles had a different transceiver element fitted in the Triffid installation.

 

Triffid was carried in Bedford MKs.