[mythtv-users] HDHR app can tune a station but Myth via HDHR can't

Douglas Peale Douglas_Peale at Comcast.net
Thu Feb 29 05:34:07 UTC 2024

On 2/28/24 20:15, DryHeat122 wrote:
> On Wed, Feb 28, 2024, 9:00 PM Gary Buhrmaster <gary.buhrmaster at gmail.com> wrote:
>     On Thu, Feb 29, 2024 at 3:37 AM DryHeat122 <dryheat122 at gmail.com> wrote:
>     >
>     > I have a HDHR Duo. For one station (Channel 12), the HDHR app can tune it just fine. When I try to "watch this channel"
>     on Myth via Program Guide, "signal" (IDK if that is strength or quality) dithers between 56% & 59% and it can't get a
>     lock. Recordings on that channel also fail.
>     >
>     > What could explain this? Every other channel works fine. I am only 9 mi as the crow flies from the mountain where all
>     the stations broadcast.  Rabbitears.com lists the signal as good. If the app can lock the signal accessing through the
>     device then Myth accessing through the device should able to also, no?
>     Yes, but.  If the signal is "too strong", the HDHR's
>     can overload their frontend(*) and the decoding
>     can fail.  And if you do not have an LTE filter, one
>     can find that the local (600Mhz) LTE signal
>     from one or more of the local mobile providers
>     results in overloads on the front end.  And,
>     lastly, sometimes too strong a signal can
>     overload the frontend too, which can require
>     a pad(**), although if your other channels
>     are (deep) fringe may require a channel
>     specific pad (which is available, but typically
>     not cheap).
>     (*) RF frontend is a well understood term
>     in EE and RF physics.
>     (**) aka attenuator
> It seems like if the first two were the case, the HDHR app wouldn't be able to tune the channel either, but it can. As for  
> too strong a signal overloading Myth, channels with higher signal strength according to the rabbitears.com 
> <http://rabbitears.com> report get locked by Myth just fine.
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I presume that by "HDHR app" you mean "HDHomeRun Config" on your linux computer? If so, you can run that in parallel with mythTV 
and see signal strength, signal quality, and symbol quality as mythTV is using that channel. You can also tell which tuner in 
the tuner box MythTV is using by looking at which one is tuned to the channel that MythTV is tuned to.

It is not clear to me which HDHR you are using, there were several versions with two inputs. The very first one had two 
independent inputs, one for each tuner. If only one is connected and MythTV is choosing the wrong one, the signal strength would 
be very bad.

It used to be that each input on those early tuners could be programmed separately on MythTV, but since later HDHomeRun tuners 
only have a single input, mythTV treats all of the tuners in a HDHR box as identical (even though the 4K box has two ATSC 3.0 
tuners and two ATSC 1.0 tuners). If you have one of the early HDHomeRun tuners with two inputs, you must put a splitter in front 
of it so both tuners see the same signal.

Another worry is that FM signals are much stronger than TV signals, and can saturate the input of the tuner or any pre-amp you 
have on your antenna. You might need an FM trap. There are two types of FM trap, and they seldom say what type they are. One 
will kill all FM, but will also kill channel 6, the other will keep channel 6 but only kills the lower frequency FM signals. 
Which one you want depends on if there is a signal on channel 6 that you care about. The easiest way to tell them apart is with 
a spectrum analyzer. Spectrum analyzers used to be very expensive, but recently they have gotten much cheaper. This one would 
probably be adequate: 

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