These last few weeks have been very busy with the change of frequency on the Mendip transmitter. The BBC channels which were being transmitted on channel 49 have moved to channel 32, on the whole this hasn’t been a problem but I have come across a couple of instances where group C/D aerials were being used. Probably a good time to explain aerial grouping then.
In the past all frequencies from Mendip were in the C/D range, which would be channels 48 – 68, and so aerials that were optimised for those frequencies were used in this area, but with the 700Mhz clearance that is going on all over the country these frequencies are being moved down the spectrum and eventually I expect all Mendip frequencies to be below channel 48 with the bulk being in the 30’s. This is fine if you have a wideband aerial but a C/D aerial has 50% less gain at channel 35 than it does at channel 56.
This has proven difficult for some still using a C/D aerial, I’ve been to a few retunes where all frequencies above channel 40 are fine but getting down to channels 32 and 33 there is no reception at all, in these cases I have had to replace the C/D with a wideband aerial, this provided an instant cure in all cases.
So a little more about the aerial groups. Starting on group A, these aerials are designed to give the best gain between channels 21 and 37, to identify these aerials they have a red bung behind the reflectors, around here group A aerials would be used for local relays like Carhampton and Porlock and for the Stockland Hill transmitter. Next comes group B, identified by a yellow bung and optimised for frequencies between channels 35 and 53, used for the Wenvoe transmitter. Then comes C/D, these have a green bung and operate best between channels 48 and 68, these were widely used for the Mendip transmitter and also for some of the local relays like Woodcombe, Washford and Kilve. Next are group K (21 – 48) and group E (35 – 68), neither have been widely used around here. Lastly is group W, or wideband, these have a black bung and cover frequencies from 21 – 60. Most aerials installed in this area in the last decade would have been wideband.
Below is a graph showing the frequency response of the different aerial groups.