mb21 - The Transmission Gallery

	UK Broadcast Transmission

THE TRANSMISSION GALLERY

CHILLERTON DOWN

Photos by Martin Watkins and Mark Carver

Page last updated: 2011-10-23

October 2011

The fact that this mast was built to a "slim-line" design by the ITA (to satisfy local planners) merely serves to accentuate its graceful slenderness. It makes Rowridge (even the new mast) look stocky and squat, towering over the BBC's efforts as viewed from almost anywhere on the island. This is explained by the fact that Chillerton Down's site height is about 30 m higher than that of Rowridge, and the mast is 80 m taller than the old Rowridge mast, and still 50 m taller than the new.

It's difficult not to feel that the ITA took rather more trouble than the BBC did with finding a site and building an adequate structure. A BBC report (to be found on the Rowridge pages of mb21) suggests that indeed the BBC was disappointed with Rowridge's performance, with relays still needed for Brighton and subsequently at Weymouth.

Long access road...

(Mark C is far too modest to mention that in fact this sign was subject to an impromptu repair at his hands - the Chillerton Down bit had fallen out of the rest of the panel and disappeared into the grass. This photo was taken after his repair efforts; does anyone know which part of Arqiva handles maintenance invoices from third parties...?)

It's not easy to reconcile the Ofcom parameter figures for agls with the reality up the mast.

Three tiers of Band II panel aerials can be seen here. The top two tiers are only on the north west and north east faces, and also contain interleaved DAB dipoles. These tie in with an Ofcom figure of 214 m agl, (DAB (block 11D) & FM 105.2 & 106.0 MHz).

The bottom single tier however has four faces distributed evenly round the mast. Ofcom has an agl of 190 m for 103.2 MHz, but we seem to be looking at a "real" height of about 209 m agl, assuming this is the 103.2 MHz aperture.

A Sira is visible bottom left. The Ofcom agl height for 107.0 MHz is 206 m with a power split of 0.02/0.08 kW, surely the hallmark of a Sira!

(picture taken from the south west)

We've subsequently been contacted by Russ Tollerfield who has clarified the situation by confirming that the damaged Yagi was (maybe still is) the reserve antenna for 103.2 MHz; in the past it's been used for an hour or so every six months during maintenance. Russ also says that 103.2 MHz uses the top tier of panels as its main antenna, with the main beam towards Southampton and a null to the south-east.

Here are the other DAB aerials, level with the second-from-top stay point. These could correspond to a listing on the Ofcom parameters at 200 m agl. (DAB Block 11C).

(viewed from the south west again)

Viewed from the east side.

Viewed from the west.

Viewed with a zoom lens from directly under a stay the degree of sag is very evident. It would be very easy to set up quite an oscillation in these top guy ropes. Of course we're far too responsible to do anything silly like that!