Again, although really a TVHeadend tweak, this may help people who have just brought the TV HAT.
I chose not to use the raspbain repository version of TVHeadend, rather I followed some instructions that used this as a source:
I am tuned to the Dover transmitter, I noticed I was not getting a full complement of channels, the MUX update package shared elsewhere on the board did not appear to install correctly, it installed the data to a different location to what was installed by default, “/usr/local/share” rather than “/usr/share/” (at least for me).
My solution was to extract the file for the location I needed (uk-Dover) from the update package and manually copy this to required location sudo cp uk-dover /usr/share/
For reference it was the channels on COM4 that were missing, even with the update MUX file you may still have to manually create / edit a MUX for COM4, note that this conflicts with the info listed at https://ukfree.tv/transmitters/tv/Dover ...
DELIVERY_SYSTEM = DVBT
FREQUENCY = 586000000
BANDWIDTH_HZ = 8000000
FEC high = 3/4
FEC low = NONE
CONSTELLATION = QAM/64
TRANSMISSION_MODE = 8K
GUARD_INTERVAL = 1/32
HIERARCHY = NONE
INVERSION = AUTO
Also worth noting, at Dover the channels broadcast on COM4 (586MHz), 5 (778.0MHz) & 6 (690.0MHz) are broadcast at a much lower power than the BBC & HD channels, if you are seeing picture breakups on some channels but not others it could well be because of this.