[mythtv-users] Antenna attenuator question

[backuppc at sundquist.imapmail.org]

On Tue, 01 Jul 2008 01:34:28 -0700, "Alen Edwards"
<allen.edwards at oldpaloalto.com> said:

> JS,
> 
> There has been a lot of discussion about multipath that came from this 
> thread.  That may or may not be your problem but as you say the problem 
> went away when you disconnected the amplifier, my bet is still on 
> overload, as you originally suspected.

I only brought up multi-path as a potential problem when I ran across
that mention in http://www.hdtvprimer.com/ANTENNAS/silver.html  that
talked about a DTV station having a strong signal but the tuner couldn't
lock (a problem due to multi-path).  To be clear, that was not the
problem I was having with NBC (5 miles to the rear of my CM4221) but
with PBS (25 miles to the front of the antenna).  However, that PBS
problem could be a complete red herring and I should leave that for
another discussion thread.

As you said, since unplugging the amplifier gets rid of pixelation, it's
probably just a signal overload issue for NBC.  The fact that I get less
pixelation lately with the amp on, during a time with much more leaf-out
on the trees and overall more stormy weather than the spring, lends
credence to this.

I'll have to try the jury-rigged attenuator you suggested, but I'll need
to get the resistors.  It would be nice if a local store carried the $2
fixed-dB attenuators.  I bet Radio Shack (only local electronics store)
will probably charge $5 for a terminator resistor.

J.S.
 
> If you have a 2 way coupler, you can make a cheap variable attenuator 
> out of it by connecting one output to your Tv and the other output to 
> your antenna lead.  This may be enough to cure the problem but if it is 
> not, put a resistor near 75 ohms on the input.  If you put a perfect 
> load on the input and the coupler were ideal, this setup would give you 
> a high level of attenuation because the signal going in the output and 
> coming out the input would be absorbed by the resistor.  If, on the 
> other hand, the input is left open, then the signal will bounce off the 
> open circuit and come out each output.  Half would go up your antenna 
> wire and stop at your amplifier.  The other half would go to your TV, 
> attenuated.  A resistor near 75 but not exactly 75 will give you a 
> variable amount of attenuation.  I tried this and it works.
> 
> 
> 
> Allen
>