THE TRANSMISSION GALLERY
|Photos by TCPD||Page last updated: 2015-01-24|
|These pictures are as interesting as they are tantalising.|
They show Bilsdale from some time in the 1980s, and apart from the first picture we're standing on the top of the UHF cylinder....
|Above: in the centre of the cylinder is this square-sided hatch, with rungs going down the top left corner.... Behind the hatch are the railings to stop one falling over the edge!|
|Here we are looking down the square-sided hatch, where can be seen that there are in fact two sets of rungs. In addition we can see what look like aerial feeder connectors of some sort, although apparently the actual feeders have gone. Each side of this access spine is 800 mm.|
|And here are the aerials, Rhode and Schwarz as far as TCPD remembers. Each of the four outer sides of the square centre spine we've seen above carried the aerial panels. |
It seems that Bilsdale had two access hatches at the top, one for the centre access spine that we've seen in the pictures above, and this one to gain access to the UHF aerials below. It can be seen that this outer hatch is specially shaped to match the curve of the main cylinder, whose diameter was 2100 mm.
TCPD tells us that these R & S panels were the original three-channel-only antenna put in when Bilsdale was built, and they only occupied the top half of the UHF cylinder. Perhaps in order to save costs, this aerial was designed for a frequency range covering chs 26/29/33 only, with ITV using ch 29.
Therefore when Channel Four came along in 1982 a completely new EMI-slot four-channel UHF aerial was built in the lower half of the cylinder; it's likely that the original R&S three channel aerial would have needed so much redesign work (power handling, bandwidth etc) that it was simpler to install a new four-channel aerial in the unused lower section of the UHF cylinder.
A mast outline of the mid-1980s shows the UHF aerial occupying only the bottom half of the cylinder, but the significance of this subtlety has only just been clarified thanks to TCPD.
From all this we can deduce that this photo was taken after the R&S aerials were decommissioned (lack of feeders on those connectors in photo 3) but they probably weren't actually removed until interim digital transmissions started in the late 1990s.
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