[mythtv-users] Best tuner? - now signal strength app - followup
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
> $ cat /sys/class/dvb/dvb0.frontend0/device/subsystem_vendor
> 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
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!
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