[mythtv-users] signal amp q?

[Steven Adeff]

On 5/15/06, Brian Wood <beww at beww.org> wrote:
> 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?
> >>
> >> Thanks!
> >
> > 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
> > with.
> >
> > 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
> > line.
> >
> > 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
> > house/apartment.
>
>
> 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
> enough.
>
> 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.

thanks for the advice guys. I think I will set all 4 of my recorders
to record and play with the signal boost control of the amp to see if
I can find a "sweet spot". they also have an 8port splitter with
builtin amp (but no gain control knob), for $120, which is a lot more
than I want to spend, but may end up being necesary. I may also run
the other cable line to the closet I'm using to house my new backend,
perhaps it just has a stronger signal than the other line...

-- 
Steve
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