@Skylark NW, such a lot has changed with TV transmissions in the time since your last aerial was installed. Before we get to that though, let me give you some good news.
The fact that your ITV signal isn't breaking up is significant. It means that the trees aren't killing all of your signal, so if you can get an aerial where the reception strength is as good for BBC as your ITV signal, then that's very likely to solve your problems.
Why are the trees causing the loss of BBC but not ITV?
This is to do with the reception capabilities of your existing aerial. In 1987, we had just four analogue channels. From Winter Hill in the Granada region, all of those channels broadcast in the upper region of the ch21~68 frequency range. The lowest was BBC1 on RF ch 55, and the highest was C4 on RF ch 65. Grouping the channels together like this allowed the broadcasting engineers to work out a way that main transmitters could overlap with their transmission areas without interfering significantly with each other.
All TV aerials work in a similar way in that they can either be broadband or tuned to a narrow frequency range. Each has its pros and cons.
Broadband aerial cover the entire frequency range, but the trade-off is that the signal power they can generate at any specific frequency is relatively low. Tuned or
Group aerials to give them their proper title, focus the reception capability in to a narrow range of frequencies. The peak of their reception efficiency is within this tuned range, so they give a much stronger signal in that range. They still receive outside that band, but at far lower efficiencies.
We still use Group aerial today. If anything, they're coming back in to fashion
I think it's very likely that you either have a Group C/D aerial (green curve: the range that best matches the analogue channel spread of the Winter Hill transmitter), or maybe a low efficiency wideband aerial (black curve). There are some other reasons for selective channel loss such as cables being trapped/crushed/bent, but Group C/D seems most logical as this would have given the aerial installer the strongest signal to match what Winter Hill was broadcasting.
What has changed?
In your case, it's the tree growth combined with changes to where the channels are now being broadcast for digital TV.
The channels being broadcast are no longer all up in the higher regions of ch 21 to 68. This is what all the digital retunes has been about. For a start, channels 60-68 are no longer available. They were sold off to make 4G mobile transmissions possible. We now have 5G mobile phones, so another part of the TV channel bands are being cleared to make way. Long term, all of the TV channels will be bunched together between ch 21 and 48. We still have some way to go before we get there, but if you're looking to future proof then this is what you need to plan for.
At the moment, the Winter Hill mux channels, in mux channel order, as received in Middlewich CW10 are as folllows. This will be the same for you, but you might also pick up the weaker Manchester local mux that's too low powered to reach me.
PSB1......BBCA.....(BBC1 SD, BBC2 SD, etc)...................mux ch 32
COM6.....ARQB.....(commercial SD channels)..................mux ch 37
COM5.....ARQA.....(commercial SD channels)..................mux ch 49
PSB3......BBCB.....(HD versions of BBC and ITV stations)..mux ch 54
COM7.....ARQC.....(commercial SD and HD channels).......mux ch 55
COM8..................(commercial SD and HD channels).......mux ch 56
COM4.....SDN.......(commercial SD channels)..................mux ch 58
PSB2......D3+4.....(ITV1 SD, Ch4 SD, Ch5 SD etc)...........mux ch 59
KEY:
Mux = short for multiplex; a way of transmitting several channels using a single frequency. This is the basis of how Freeview digital TV offers more channels than the old analogue service
PSB = Public Service Broadcast. These are the stations that every house that receives Freeview should be able to pick up.
COM = Commercial stations outside of the PSB remit. You'll get these from a main transmitter such as Winter Hill or Emley Moor in Yorkshire, but not from the smaller repeater stations such as Saddleworth
SD = standard definition; these are channels that any Freeview receiver should be able to pick up as long as the mux is broadcasting signals suitable for a DVB-T* tuner
HD = High Definition; channels only suitable for a TV with a Freeview HD tuner
DVB-T = the basic Freeview transmission standard used on the PSB muxes
DVB-T2 = a newer version of broadcasting Freeview which enables the transmission of HD channels
* = some SD channels broadcast in the COM muxes require a TV with a HD-capable tuner even though the channel itself isn't HD
For someone installing an aerial today, they could choose a wideband high-gain aerial but I think that would be quite short-sighted. The frequencies it works best with will be empty in a few years. A better choice is a Group T Log Periodic aerial - A
Log 36 to be precise. This provides good reception from ch 21 to ch 60, so works well for transmissions today. Also, because the gain curve is relatively flat, then any reallocation of the channels won't make too much of a difference to the reception strength from the aerial. It's a good long-term bet.
If required, some amplification can be added to help cope with the signal reducing effect of all that water in the leaves and branches. Depending on the trees and how they grow, there may come a time though when either thr trees have to be cut back, or you switch to an alternative such as satellite reception (Freesat)
If this advice or any other reply was helpful to you, then please do the decent thing and click the T-H-A-N-K-S button; that's thanks, not like, there's an important difference. It appears when you hover the mouse pointer near the Quote Multi-quote buttons. It costs you nothing. This is the proper way to show your thanks for the time and help someone gave you.
