[mythtv-users] Special needs dad with MythTV hardware questions

Stephen Worthington stephen_agent at jsw.gen.nz
Sun Nov 24 00:17:08 UTC 2013


On Sat, 23 Nov 2013 17:18:35 -0500, you wrote:

>On 11/23/2013 04:43 PM, Jerry wrote:
>> On Sat, Nov 23, 2013 at 3:47 PM, <mythtv-users.jim-j at mamber.net
>> <mailto:mythtv-users.jim-j at mamber.net>> wrote:
>>
>>     [Which tuner(s) to buy]
>>     My only source of TV is an antenna in my attic for receiving digital
>>     OTA TV.
>>
>> I have a HDHR Prime with 3 tuners and it only has one cable connection.
>> I think you'll be fine with a HDHR (non-prime).
>
>The early HDHR's are alleged to have less sensitive tuners than, for 
>example some tvs. IIRC the HDHR Prime is for CABLE ONLY. I have 2 HDHR's 
>with one being fed from a pre-amp and they give me no problems.
>
>I have a 2250 and usually it is being fed analog cable. (No unencrypted 
>QAM available). Testing shows that it is quite good for ATSC. I have 
>found that it needs to have the modules loaded in a particular order.
>
>Both the HDHR and 2250 have only one coax input.

Having only one coax input for a dual tuner card does not mean that
the tuners only have one input - usually, there is an internal
splitter, with the usual signal loss that comes from a splitter: each
tuner will be getting a little less than half the signal.  So if you
have signal problems, a dual tuner is normally going to be one
splitter less sensitive than two single tuners or a dual tuner with
two separate unsplit inputs (if they exist).  And with a dual tuner
card, there is no way to avoid the extra internal splitter, so the
dual tuners will always be getting a lower signal level than your TV
which only has a single tuner and no extra splitter between it and
your aerial.

As a simple example, say you currently have two TVs on your aerial.
There will be a splitter and each TV is getting half the signal.  If
you replace one TV with a dual tuner, the other TV will still be
getting half the signal, and each of the dual tuners will be getting a
quarter of the signal.  However, if you install two separate tuners
alongside the TV, and change the two way splitter two a three way one
to do that, then the TV and each single tuner will now be getting
around one third of the signal.  The TV is now getting less signal,
but each tuner is getting much more.

So: If you are already marginal on signal levels, adding a dual tuner
is a bad idea.  If you unplug an existing box from the aerial and
replace it with the dual tuner, you are likely to get reception
problems.  You need to fix the signal levels by adding an amplifier or
upgrading the aerial first.  The easy thing to do is try adding an
amplifier/splitter where you are adding the new tuners.  That may work
if the signal is OK at the point it is split, but you may find that
the signal was already to degraded at that point and the amplifier
needs to be on the aerial itself, or at least at the first point the
coax comes into the house.  And in that case, you need to be able to
run more coax from the amplifier to where it is needed.  So what I
would recommend is see if you can borrow an amplifier/splitter from
someone for a few hours to try it and see if it works where it is easy
to install near the equipment.  If it does, fine, get one for
yourself.  If not, then the budget needs to include upgrading the
aerial system.  Of course, you need to have a dual tuner to test with
as well, and they are less easy to borrow.

This caution applies to everything that has multiple tuners builtin,
including things like TiVo boxes - unless you know it has something
other than a simple splitter sending the signal to its multiple
tuners, you must assume that it will actually have a splitter and you
will need to have a good enough signal to overcome the loss from the
splitting.  And the more tuners it has, the more loss from the
splitting.


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