Mangerton is right that Crystal Palace, where it is most likely your service and the 9 multiplexes there come from, are set in the low channel numbers, 20s and 30s, well away from the 4G signals which are beyond channel 60 at the top of the band. IOW direct interference from a base station is unlikely provided you have a filter in the aerial lead to block the 4G which sits where some DTT signals used to be [see post #2 above for Dave].
Selective loss of multiplexes is odd but suggests targetted channels - ie specific frequencies are affected - which then suggests a frequency selective problem. This could be propagation related - strong semi-permanent echoes [the Canary Wharf problem] from tall buildings in the path that escape the guard interval of the robust modulation used [especially on the HD multiplexes] but this seems unlikely given the short distances between you and the transmitters [about 15km depending where in Central London you are] or a local installation problem leading to a mismatched aerial lead. This seems unlikely if you've had professional people to do the installation, let's hope they can find and fix the problem for you. In London spurious transmissions not to say pirates are not out of the question.
However, your description of the problem suggests that the causal source is variable, a retune works for a while and then fails. Your TV memory should keep track of where the signals are once its first tuning is done and so even if the signal faded out the receiver still knows where to look when it is there so that if you tune in to a specific service the receiver will find it. These intermittent problems are annoying!!
Another outside possibility is that, being so close to the powerful transmitters at CP [200kW for most but a lot less for the Local London and some of the HD ones], you have too much signal!! This can often cause as much trouble as too little by overloading the receivers. Do the new HD channels in 33 and 35 which are at much less power remain stable? The aerial guy on Monday should check this for you.
Selective loss of multiplexes is odd but suggests targetted channels - ie specific frequencies are affected - which then suggests a frequency selective problem. This could be propagation related - strong semi-permanent echoes [the Canary Wharf problem] from tall buildings in the path that escape the guard interval of the robust modulation used [especially on the HD multiplexes] but this seems unlikely given the short distances between you and the transmitters [about 15km depending where in Central London you are] or a local installation problem leading to a mismatched aerial lead. This seems unlikely if you've had professional people to do the installation, let's hope they can find and fix the problem for you. In London spurious transmissions not to say pirates are not out of the question.
However, your description of the problem suggests that the causal source is variable, a retune works for a while and then fails. Your TV memory should keep track of where the signals are once its first tuning is done and so even if the signal faded out the receiver still knows where to look when it is there so that if you tune in to a specific service the receiver will find it. These intermittent problems are annoying!!
Another outside possibility is that, being so close to the powerful transmitters at CP [200kW for most but a lot less for the Local London and some of the HD ones], you have too much signal!! This can often cause as much trouble as too little by overloading the receivers. Do the new HD channels in 33 and 35 which are at much less power remain stable? The aerial guy on Monday should check this for you.
- both run off the same aerial but are different, apparently - it supplies TV signals but not as strongly. I've no idea why for 8 or 9 months, it was sufficient to provide all channels, and then over the last 2 months changed its ability to do so... 
) at signal strength 10/10. 
Comment