[mythtv-users] Best tuner? - now signal strength app - followup

DaveD mythtv at guiplot.com
Wed Feb 3 17:02:32 UTC 2021

On 1/13/21 2:29 AM, Vincent McIntyre wrote:
> On Tue, Jan 12, 2021 at 08:53:16AM -0800, DaveD wrote:
>> After a couple of days, I stopped checking the data and let it run for a
>> week before looking again.  Unfortunately, after about 3 days the logged
>> card started to always be "unknown".  That's the default.  When the program
>> starts, it checks for adapters by listing /dev/dvb.  It then finds the chip
>> for each adapter using "dmesg | grep 'DVB: registering adapter '" which lets
>> me build a unique name for each card.  The problem occurred when dmesg got
>> overloaded with messages and the old ones were dropped.  No more output from
>> the dmesg | grep command.
> You might make things a little more reliable by fishing round in /sys.
> $ cat /sys/class/dvb/dvb0.frontend0/device/subsystem_device
> 0xdb78
> $ cat /sys/class/dvb/dvb0.frontend0/device/subsystem_vendor
> 0x18ac
> These can be translated with /usr/share/misc/pci.ids as
> 18ac DViCO Corporation
> db78 FusionHDTV DVB-T Dual Express
> It is a little more complicated as different cards have different
> contents under /sys. It is probably worth messing around with udev
> to see if you can cast a spell that gives you the info you require.
> e.g. give this a go
> $ udevadm info -a -p $(udevadm info -q path -n /dev/dvb/adapter0/frontend0)
> $ udevadm info -a -p $(udevadm info -q path -n /dev/dvb/adapter0/demux0)
> Plus, udev has some kind of api which may help you with this.
> I'm interested to see this code as well if you are game to share,
> I have the same setup with dvico dual & hauppage quad, and glitches.
> Kind regards
> Vince

Thank you, Vince, for the insight into the /sys, but my Fedora 31 
distro's version of pci.ids gave me wrong information for one of my 
tuners.  udevadm info seemed like a good shot, as well, but turned up 
nothing related.  Using dmesg for building a unique ID for each tuner 
still works the best and handles the case when I plug in my USB tuner, 
as well.  What I did to get around the ring buffer limitation was a cron 
@boot command "dmesg > /tmp/dmesg.out" to record the internal cards' 
info before it gets dropped, and then resort to reading that file when 
the current dmesg output stops finding the adapter.  It's a hack, but 
works. New version of the program is available at 

I am so glad I wrote this program.  I have no idea how I would have 
gotten my antennas (yes, plural) adjusted without it.  I took my laptop 
to the attic and moved the VHF antenna around to get the best reception 
on those channels, then did the same with the UHF. I would never have 
guessed that the locations and directions I ended up with would give me 
the performance I'm getting.  Being able to carry the antenna around and 
turn it while watching the app display signal strength on big, visible 
bar graphs made it all possible.

I'm using a DB8e 8-Element Bowtie for UHF and a ClearStream 5 for VHF, 
both from Antennas Direct.  Both perform pretty well, for their 
respective bands, and they tuck nicely into the attic (unlike the beam 
antenna I had before, which also didn't let me point them differently 
for different bands).  I have a preamp with dual inputs that boosts some 
channels a bit and doesn't degrade any channels, all easily measured 
(and logged) with my app.

I am now getting all local channels reliably (finally!).  I have been 
logging the signals twice/hour of all of them for several days and have 
been getting excellent results in spite of the crappy weather.  Not one 
instance of pixellation in any recording, so far, in weather that would 
have rendered unwatchable recordings before.  Thanks to all who have 
helped me in this endeavor.  Now I can relax and watch some TV!

Dave D.

More information about the mythtv-users mailing list