[mythtv-users] signal amp q?

Steven Adeff adeffs.mythtv at gmail.com
Mon May 15 12:52:05 EDT 2006


On 5/15/06, Joe Votour <joevph at yahoo.com> wrote:
> --- 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.
>
>
> Yes, you are correct, it could be too strong of a
> signal also.
>
> In my experience, I've never had too strong of a
> signal coming into the residence, but then again, I've
> always lived in apartment complexes where the signal
> is split a ton of times before getting to me.  In a
> house, it is quite possible that they amplify the
> signal before it goes into the house, on the
> assumption that the homeowner will split it and get
> the level "just right".
>
> Here at the office where we basically have our own
> cable plant, we do wind up with too strong of a signal
> at times and place attenuators where necessary.

I should mention that I only really notice the issue on my analog
stations through my cablebox, my three HD tuners seem ok and the
digital channels aren't so bad, just the old analog channels...

I don't know if this helps any...

I saw an 8 channel splitter with built in amplifier, but it had no
gain control, and was $120... is this a fixed gain amp or is there
some auto-attenuation going on?


-- 
Steve
Before you ask, read the FAQ!
http://www.mythtv.org/wiki/index.php/Frequently_Asked_Questions
then search the Wiki, and this list,
http://www.gossamer-threads.com/lists/mythtv/
Mailinglist etiquette -
http://www.mythtv.org/wiki/index.php/Mailing_List_etiquette


More information about the mythtv-users mailing list