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

Stephen P. Villano stephen.p.villano at gmail.com
Sun Nov 24 02:05:47 UTC 2013


On 11/23/13 7:17 PM, Stephen Worthington wrote:
> 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.
A bit oversimplified. I've had splitters that have anywhere from 5-15 db
loss, depending on how many outputs and the model.
Then, between 3-5 db loss for the connector.
With an internal splitter, that loss is typically in the 5-7 db range,
in my experience. Granted, that experience is around 15 years back, but
the laws of physics don't change all that often. One does lose the
insertion loss of connectors, if the tuner is on board.
> 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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