[mythtv-users] signal amp q?

[Joe Votour]

--- 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!
> >>
> >> --  
> >> 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
> >> _______________________________________________
> >> mythtv-users mailing list
> >> mythtv-users at mythtv.org
> >>
> >
>
http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users
> >>
> >
> > 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.
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>
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> 


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.

-- Joe

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