The card registers two frontends, frontend0 (RTL2832, DVB-T), and frontend1 (MN88473, DVB-T2), but only one demux device (demux0).
If I scan with frontend0 then mythtv detects only DVB-T channels. I read that some device drivers had a hack to automatically retry tuning as DVB-T2 requests.
If I scan with frontend1 then mythtv fails since it tries to open demux1 which does not exist. The scan eventually completes but with no channels.
So we need to rename frontend1 to frontend0. I couldn't find a modprobe to do it so resorted to this (run via sudo -s):
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cd /dev/dvb/adapter0 && mv frontend0 frontend99 && mv frontend1 frontend0
(An alternative way _might_ be to symlink demux0 to demux1, but that didn't work for me).
Delete the capture card, re-add it and then you can then scan via frontend0 and it works and gets both DVT-T2 and DVB-T channels, but I only got one of the HD multiplexes. Explicitly scanning the correct frequency (remember to select mod=DVB-T2) did not detect the channels either using the frequency from tvheadend gui in its configuration / dvb inputs / services / mux and comparing the mux column against mysql frequency column to find the missing frequency:
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mysql> select mplexid,frequency from dtv_multiplex where sourceid=4 order by frequency;
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select name,sourceid from videosource
So I went back to capture card and updated signal timeout from 1000ms to 5000ms. Then went back to scan single frequency and also set bandwidth to 8Mhz. I made both changes at the same time so can't say if one was the correct fix.
This time the scan worked and detected the missing channels and it now works fine in mythtv. It seems that the full epg for all channels is carried on the HD multiplex since it quickly populated the programme guide.
Since it is a new purchase, I can't vouch for durability of the card, reliability, warmth, etc. It's a relatively cheap card but is single tuner, whereas most dvb-t cards are dual tuner. I couldn't test the DVB-C capability. Some things that didn't work for me might work properly if I had rebooted and deleted all cards between attempts.
For scanning DVB-T2 channels outside mythtv (for testing purposes) I needed to use dvbv5-scan instead of w_scan, with dvbv5-scan being considerably faster since it uses transmitter lookup tables rather than a full frequency scan. The w_scan would only detect DVB-T channels.
In tvheadend the card shows up as three separate tuners (DVB-C, DVB-T, DVB-T2). I enabled only the DVB-T2 and it scanned all the channels without any frontend modifications necessary.
On FreeBSD, the webcamd only creates frontend0 so it couldn't tune dvb-t2 at all. The webcamd debug showed it recognizes the MN88473 but it's not attached and only sends rtl28xx commands.
Output from Linux dmesg:
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mn88473 7-0018: Panasonic MN88473 successfully attached
DVB: registering adapter 0 frontend 0 (Realtek RTL2832 (DVB-T))...
DVB: registering adapter 0 frontend 1 (Panasonic MN88473)...