[mythtv-users] ATSC tuner advice wanted

Jim Abernathy jfabernathy at gmail.com
Sun Aug 22 09:37:39 UTC 2021

On 8/22/21 12:06 AM, Stephen Worthington wrote:
> On Sat, 21 Aug 2021 17:10:22 +0000, you wrote:
>> None of the consumer based tuners tend to have
>> great RF tuner/demods (at least compared to
>> your average TV, which tend to have much better
>> RF devices).
> The most likely cause of tuners appearing to be worse than TVs is that
> most tuners these days come in multiples, or are used in multiples. To
> get signal to each of the tuners, the incoming signal needs to be
> split, so if you have two tuners in a unit and only one aerial
> connection feeding it, each tuner will be getting just less than half
> the signal that is coming in on the aerial connection.  So a TV with
> one aerial connection feeding one tuner will be getting twice as much
> signal as each of the dual tuners.  Splitting a signal four ways is
> even worse.  I think that it is probably a myth created by this effect
> that makes people say that TV tuners are better.  As far as I know,
> manufacturers use the same chipsets in tuners and TVs.
> Fortunately, a number of the latest tuners seem to have a decent fix
> for this problem.  Instead of just using passive splitters, they have
> an amplifier/splitter, so each tuner gets fed a signal that is the
> same level as the incoming signal.  There will be a slight decrease in
> signal quality from passing through the amplifier/splitter, but
> because the chips doing this seem to use quality low noise processing,
> the degradation is minimal.  This is what my TBS-6909 (8 x DVB-S2) and
> TBS-6209 (8 x DVB-T2/DVB-C) PCIe cards do, and the result is
> excellent.  I hope that the latest ATSC devices will be using this
> technology too.
> So when choosing a multi-tuner unit now, you need to be looking for
> one that uses a builtin amplifier/splitter.  But it is quite difficult
> to tell from the advertising which ones do and which ones do not. Ones
> with four or more tuners seem to be likely to be working this way, and
> the more modern design the better as the chipsets that have the
> amplifier/splitter are relatively new (maybe five years old?).
> With manufacturers who do answer questions (SiliconDust?), I would ask
> them and see what they say.
> If you have multituner devices that do not have an amplifier/splitter
> builtin, you will likely need to use your own low noise external
> amplifier, and preferably one that has adjustable levels.  These are
> typically not the units you can buy retail.  Retail units often use
> low quality (higher noise) amplifiers and offer no controls at all.

I have a Silicondust HDHR Quatro running on V31 backend It was added 
with default setting in the tuner and connection setting of mythtv-setup 
with the exception of in tuners I turned off the EIT scanning. I added 4 
tuners and 4 connections. However, I can have 4 shows recording with 
overlapping times and occasionally see as many as 6 or 8 tuners in 
action.  Particularly, if use the sub channels like 5_1, 5_2, 5_3.

This is the same behavior I see on a different backend with a Hauppauge 
WinTV Quad PCIe card.

Jim A

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