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on UK Free TVWhilst developing the new reception prediction system, I went looking for the reference material relating to the UK Aerial Groups system.
On page 39 of a document entitled 
To assess the loss of coverage as a result of moving outside of the receive aerial group, account needs to be taken of the performance of receive aerials.
For planning purposes the UKPM assumes that the gain of a receive aerial system is 7dB. This is a somewhat idealised figure based on a good aerial and feeder and no pre-amplifier. The performance of actual receive installations is known to vary considerably from this ideal. Two studies, one for the Virgin consortium that bid for the Channel 5 licence in 1995 and the other for the ITC in 2004 investigated the actual received level for a large sample of domestic installations. This study considered aerial group but not the performance of actual receive installations.
In addition to variability in receive aerial system gain, most aerials are banded and their performance falls away outside their design operating band. The ITC as part of the documentation for the original DTT plan, Notes for applicants on coverage of Digital Television, October 1996, listed the out of group response of representative receive aerials.
I have reproduced the information from the table as a graph. The values are the attenuation (in dB):
It is interesting to note that in group A, C37 is -2dB and "in group", group B, C35 is -3dB and C36 is -2dB and "in group", group C/D has C48 on -1dB and "in group" and group E has C37 or -2dB and C38 and C39 on -1dB and be "in group".
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ATV Stock Aerial Tests has some interesting comparisons between different aerial types. What is especially interesting, and this ties in with your data Brian, is how the gain of an antenna falls away rapidly out of band. This is especially true of Band A and Band C/D types.
I've just got back from a trip over to Scotland and i've noticed driving back through parts of Galloway huge aerials appearing in areas very recently. Being quite sad i notice these things! Unix 100's, some of which are vertical?? Has someone figured out the old Belfast trick by changing the polarisation they can attenuate Caldbeck's power signal? There's other rigs cropping up like those in the west of Ireland, those grids with the huge reflectors and tiny 5 element yagi's cable tied to the front of them. What that does to help signal i have no idea as they were sh8te for RTE. Worryingly these sort of things are cropping up in villages - A small village near Glenluce has 5 properties with these on the rooftop.
That is a VHF corner reflector and they're used in the states but never here as far as i'm aware. Some of those things are just vhf butchered logs with a yagi stuck to the front of them. Whoever is putting these things up must be aware that antiference double 8 & 13 logs are for band 3... Strange but i suspect dangerous knowledge being passed around by rogues.
Jordy: I was up the top of a large hill near Wolverhampton and you could see four main transmitters from there Sutton Coldfield, The Wrekin, Brierley Hill and in the far distance Ridge Hill.
As for the picture that I took from a car on the A38 of Sutton Coldfield...
Gain (curves), Again
