Jeff: The Valley meanders quite a bit which means you are quite a way off having line-of-sight, with several peaks in the way within four miles of your location. The engineering works could necessitate the transmitter using its reserve antenna and/or going on low power. The reserve antenna is a bit down the mast from the main one at the top, and considering the obstructions in your way, it's easy to see that a reduction in height of the antenna in use at the transmitter could result in difficulty with reception.
Here is a terrain plot between your location (on the left) and the transmitter (on the right):
The local multiplexes carry only a few programme channels and use a signalmode which is more resilient. There is a trade-off which means the signal mode employed can't carry as many programme channels.
With respect to the predictor computing "good" reception on COM5 (C33) and the PSBs, "poor" on COM6 (C36) and non-existent on COM4 (C48) then I believe the interfering, co-channel transmitter here is Sutton Coldfield with its two Local TV multiplexes. C48 broadcasts southwards and westwards and C36 which is northwestwards.
Whenever the predictor throws up a result such as this where one or more channels are markedly down on the others, despite them all coming from the same transmitter and at the same power, I have a look around to see if I can work out which transmitter (or transmitters) the predictor may be factoring as possible interferer(s). I seem to recall this isn't the first time I've seen a prediction for Mendip to the south of Sutton Coldfield where C48 has been computed by the predictor as quite a bit down on C33 and C36. Whether this is realistic in practice or whether it is rather pessimistic (in that the potential for interference has been over-exaggerated) I'm not sure.
Thursday 28 November 2024 12:19PM
Jeff: The Valley meanders quite a bit which means you are quite a way off having line-of-sight, with several peaks in the way within four miles of your location. The engineering works could necessitate the transmitter using its reserve antenna and/or going on low power. The reserve antenna is a bit down the mast from the main one at the top, and considering the obstructions in your way, it's easy to see that a reduction in height of the antenna in use at the transmitter could result in difficulty with reception.
Here is a terrain plot between your location (on the left) and the transmitter (on the right):
Terrain between ( m a.g.l.) and (antenna m a.g.l.) - Optimising UK DTT Freeview and Radio aerial location
The local multiplexes carry only a few programme channels and use a signal mode which is more resilient. There is a trade-off which means the signal mode employed can't carry as many programme channels.
With respect to the predictor computing "good" reception on COM5 (C33) and the PSBs, "poor" on COM6 (C36) and non-existent on COM4 (C48) then I believe the interfering, co-channel transmitter here is Sutton Coldfield with its two Local TV multiplexes. C48 broadcasts southwards and westwards and C36 which is northwestwards.
Whenever the predictor throws up a result such as this where one or more channels are markedly down on the others, despite them all coming from the same transmitter and at the same power, I have a look around to see if I can work out which transmitter (or transmitters) the predictor may be factoring as possible interferer(s). I seem to recall this isn't the first time I've seen a prediction for Mendip to the south of Sutton Coldfield where C48 has been computed by the predictor as quite a bit down on C33 and C36. Whether this is realistic in practice or whether it is rather pessimistic (in that the potential for interference has been over-exaggerated) I'm not sure.