[mythtv-users] Antenna attenuator question

backuppc at sundquist.imapmail.org backuppc at sundquist.imapmail.org
Mon Jun 30 19:41:36 UTC 2008

Thanks Brian and Allen for offering some advice.

Some of my thoughts:

Brian wrote:

> You might want to look into a tunable trap, which allows you to reduce
> the level of the strong local channel while leaving the rest of the
> channels more or less alone.
> Also, things like strong local FM stations can cause problems with
> amplifiers. You can get either tunable FM traps to null out a strong
> station, or you can get traps that take out the entire FM band.

That sounds like what Allen was suggesting:

> There is actually a product made just for what you are trying to do.
> It would be for a case where the signal was even stronger that what is
> probably the case in your situation but if you continue to have
> trouble, it is worth knowing about. It can attenuate just the one
> signal. This one could go in front of the amplifier and prevent it
> from being overloaded.
> http://www.summitsource.com/product_info.php?ref=1&products_id=5344
> It will attenuate just the strong signal. Because it so strong, it is
> far from the noise so you don't care that you are making its S/N
> worse, it will still be more than good enough.

But before I dropped $60 on one of those, I may try the re-aiming
approach after all.  I am beginning to think I have some multi-path
problems now that the antenna is on the roof, and that is what is giving
me the problems with NBC.  I am thinking that after reading
http://www.hdtvprimer.com/ANTENNAS/silver.html which, despite being
specifically about the silver sensor, has a more general discussion
about long-delay multi-path problems.  I've got a much taller house next
to me, and trees all around (although I did my best to put the antenna
out of the path of the biggest ones).  But this sentence from the silver
sensor page: "The signal is strong, but the DTV just won’t lock-on."
describes a separate problem I have, namely pulling in PBS.  I was going
to work on that some more before asking for help, figuring it was a
software problem, not an antenna problem.  Maybe repositioning the
antenna will help both problems.  The PBS station (located in the
direction the antenna is aimed) has a strong signal but can't lock,
although the other stations with transmitters near it lock well.

If I run out of luck with that, I'll try the variable attenuator route,
first.  It's maybe $20 more than a selection of single fixed
attenuators, but as Brian said:

> On Monday 30 June 2008 07:03:18
> backuppc[at]sundquist.imapmail.org wrote:
> > If this attenuator is the ticket, hopefully I can find a magic
> > setting that will balance the strong and weak signals.
> The problem with that type of attenuator is that it lowers the level
> of all signals, the strong as well as the weak.

...hopefully I can get just the right setting since "weak" signals are
pretty strong with the amp.  I'd degrade them just enough so that NBC
would stop pixelating.

BTW, Allen said:

> You also want your amplifier before the cable. I hope you were
> talking about unplugging the amplifier power supply downstairs and
> not the actual amplifier. I have a very similar amplifier. These are
> made to go on the antenna pole itself. I didn't want to do that so
> mine is in the attic right at the antenna lead-in, which goes through
> a pipe in the roof so that the distance from the antenna and the
> amplifier is only about 10 feet. If you can't do that, put the
> amplifier on the pole.

The amplifier itself (the black box) is up on the pole next to the
antenna.  The power supply (the white box) is inside just after the
cable comes into the house. The installation instructions actually say
put the power supply close to the tuners.  It is indeed the power supply
that I unplug.

Thanks again for the help.


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