[mythtv-users] signal amp q?
beww at beww.org
Mon May 15 00:50:35 EDT 2006
On May 14, 2006, at 9:50 PM, Joe Votour wrote:
> --- Steven Adeff <adeffs.mythtv at gmail.com> wrote:
>> not exactly the best place to ask, but I figure
>> maybe someone has some
>> experience in this area...
>> I've got a signal that is capable of feeding at
>> least 1 tuner without
>> amplification, but I'm splitting it into four,
>> possibly up to 6 soon.
>> So I purchased a 10-25db gain amp (the Lutron from
>> Home Depot) along
>> with the 6 channel splitter they have. But it looks
>> like this
>> combination won't even handle 3 tuners pulling in a
>> signal. I've had
>> all 4 current tuners run off our other, seperate,
>> line running from
>> the pole at the same time, so I'm puzzled as to what
>> the issue could
>> be, possibly a faulty splitter?
>> anyone have any ideas for me to try?
>> Before you ask, read the FAQ!
>> then search the Wiki, and this list,
>> Mailinglist etiquette -
>> mythtv-users mailing list
>> mythtv-users at mythtv.org
> A six way splitter has 11dB loss (or thereabouts -
> it's somewhere between 7.5 and 11 anyway) which is a
> lot to lose, especially on a weak signal to start
> Installing a signal amplifier will only work on a good
> signal - a noisy signal will just cause the noise to
> be amplfied. In fact, I found that with my PVR-500, I
> actually get a better signal if I take out the
> amplifier/splitter and hook it up straight to my cable
> I'd make sure that the incoming signal is actually
> good first. This may be outside of your control,
> depending on where the wires come into the
All good and true, and sound advice.
It is also possible that you are getting into trouble in another way
though, too much signal can cause at least as many problems as not
The amplifier will have a maximum output rating, probably based on
how many channels (ie: you can run at a higher output level if you
have fewer channels). If your input level plus the gain you are set
at (up to 25 db. you say) is higher than t he rated O/P level you
will get what appears to be noise but is actually third-order
distortion products, composite triple beat, "cross-mod" or whatever
you want to call it.
I'm not familiar with that particular amp, but commercial
distribution amplifiers normally run at output levels ranging from
35-45 dbmv. per channel with 35-40 channels (assuming an amp with
push-pull design of good quality).
Push-Pull design is necessary for cable signals because otherwise the
second harmonics of the low-band channels (2-6) will fall right in
the middle of the mid-band (14-21) and cause beats. "Antenna" type
amplifiers are often single-ended (not push-pull) because the
frequencies used for off-air channels are not subject to that sort of
problem. If you are using an "antenna booster" type amplifier for
cable signals you will usually run into trouble.
With modern cable systems problems due to insufficient levels are
much more common, but I just wanted to point out that other types of
problems are possible as well, and often can be difficult to
differentiate from simple "noisy" signals.
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