Where is this aerial?

[Station X]

Does anybody know where this aerial is and what its purpose was?

This picture is taken from this BBC item concerning "Numbers Stations".

http://www.bbc.co.uk/news/magazine-24910397

[mickjjo]

A right click on the picture and "view image info" gives the following:-

"An image of the antenna that used to sit behind the Dorchester in London"

Edit, There is another picture of the Dorchester aerial on this site:-

http://cogitz.wordpress.com/2009/08/...us-broadcasts/

Hope that helps a bit.

Regards, Mick.

[G4XWDJim]

Here's another more up to date picture of Deanery Street London taken from Google maps. Not quite the same angle as the original but clearly the same place. I wonder how much interference it would pick up if it was still there. Probably be unusable.

I didn't think to use Google earth to see if I could see any bracketry on top of the building but I'll do that now.

Jim

[G4XWDJim]

This looks like the place where the tower could have been mounted.

What's that old saying about the devil making work for idle hands. Never more appropriate.

Jim

[mickjjo]

There is an episode of "Minder", series 4 episode 4, "Sorry Pal, Wrong Number" with shots of Deanery Street:-

http://www.minder.org/locations/S04E...rongNumber.htm

Might be worth checking to see if the aerial is visible, (Great fun this detective work!)

Regards, Mick.

[Station X]

Thanks for the lead Jim and thanks to Mick too.

I wonder who operated the aerial and what it was used for?

[Station X]

It could perhaps have been used by The Egyptian Embassy in South Audley Street?

[Radio Wrangler]

It looks like a large log-periodic array. Size is difficult to judge but it probably covers 8-50MHz without any gaps and gives gain similar to a 2-element beam. You'll find them in the Rohde & Schwarz catalogue/webpage.

Government agencies use them on receive for monitoring and also DFing intruders and interference sources. For transmit, few transmitters need an antenna with gapless coverage few organisations have anything other than assigned spot frequencies, or assigned bands.

The exceptions are embassies and spooks.

Diplomatic traffic is heavily encrypted. They used to use teleprinter formats, but nowadays spread spectrum is more attractive, and the log periodic plays into that market.

David

[G4XWDJim]

Originally Posted by Station X

It could perhaps have been used by The Egyptian Embassy in South Audley Street?

If we could've estimate it's frequency coverage it might give us a clue. I find it difficult to estimate it's size from the original picture.

We need a local to give us a clear new picture of the roof.

Jim

[G6Tanuki]

It looks like a wire beam - the modern version being the likes of this: http://www.g3tpw.co.uk/

[m0cemdave]

I'd guess that was a foreign embassy.
There used to be quite a few impressive rooftop aerials on such buildings in London in the 70's and 80's, a particularly fine example being the big LPDA on the Chinese embassy at the time.
Of course, the ever-discreet Brits just used verticals, doubling as flagpoles, with base mounted ATU's remotely controlled from the radio room.
I presume they have all changed to satellite and secure internet systems now.

[Station X]

The trouble with satellite and internet communication is that they rely on infrastructure over which the user has no control. So it wouldn't surprise me to learn that HF radio is still in use by embassies. Coding machine, transceiver, aerial and standby generator at each end and you're totally self sufficient communicationswise

[m0cemdave]

Well, one would have thought so. But good old HMG thinks otherwise, no HF back to Blighty any more!

And that aerial does appear to have been on the Egyptian embassy.

[mickjjo]

A clear image of the Dorchester antenna:-


http://99percentinvisible.org/wp-con...a_closeup.jpeg

Regards, Mick.

[m0cemdave]

That's a good picture. It's obviously an LPDA, as David (RW). advised earlier.

[camallison]

There was a similar one on a rooftop between Berkeley Square and one of the roads leading off Halkin Street, up until about 10 years ago.

Colin

[antenna441]

This design of LP array lends itself to being rotated, however in this instance it must be fixed, as you can see that the coax goes direct to the feed point. also the coax seems to be the only cable, so no rotator. My impression is that it's a bit small to be broadcast H.F. lambda/4 at 26megs is 2.8 metres. the front end looks to be smaller than that. Very interesting...

[Radio Wrangler]

Very definitely an embassy "phone home" job. They need to vary the frequency to suit the MUF, but they're interested in only one route, so a log periodic and no rotator.

I miss the sound of Piccolo.

David

[dseymo1]

Originally Posted by Station X

The trouble with satellite and internet communication is that they rely on infrastructure over which the user has no control. So it wouldn't surprise me to learn that HF radio is still in use by embassies. Coding machine, transceiver, aerial and standby generator at each end and you're totally self sufficient communicationswise

Indeed, that's pretty much the point made in the original article.