[Hidden-tech] Weird interference with TV reception

[ussailis at shaysnet.com]

The problem could be a change in multipath conditions. Then it might not
be. But I have a problem with it here in Florence Here's what this is:

First, the media likes to tell us that digital TV is better. Fact is it
isn't, unless you only consider the lack fringe signals & "snow." Looks
like the FCC is planning another change in frequencies. If so, it will help.

The problem now is the transmission is done with a phase modulated (PM)
signal. You can consider PM to be a very close cousin of the frequency
modulated signal, FM, on your car radio.

Now I am sure you have heard noise on your favorite FM station occasionally
when you pull up to a light. Typically what you might do is move a wee
forward, and the noise either gets worse or goes away. That is a multipath
effect.

Multipath means that there is more than one propagation path from the
transmitter to your car radio antenna, and the two (or more) signals are
almost out-of-phase. So they cancel. If they are almost, but not quite
out-of-phase they almost cancel out, & you hear noise, just as if there was
a week signal...which it is.

Now modern over-the-air digital TV has the same problem. Ever notice that
on a windy or rainy day the signal occasionally goes away? Mine does when I
watch CT public TV (CPTV). Sometimes I see this on Ch 22. Commonly on CH 3
from CT. 

Now there is another issue which could be your problem. Any metal structure
causes multipath, even the wires in your home. Changing the conditions on a
wire can cause the signal re-radiated form that wire to change in phase or
intensity. That is, the path conditions change.

What I suggest you try is to move your TV antenna to see if you can recover
some of the picture. The 'trick' here is move the antenna in small
increments & then stand back. Wait some for the TV to acquire the signal. 

How to move the antenna? That you need to try. rotate, fore, aft, etc. Who
knows. The propagation gods are not too communicative. 

A fellow down the street aimed his outdoor antenna slightly upwards. About
10 degrees. I tried it here, and the signals from the more distant channels
improved. My antenna is nothing elaborate, and inside, ready to go outdoors
when warm Wx comes about.

How did I learn about this? Back in 1960 we built a FM car radio converter
and installed the first unit in the boss's T-bird. He drove over the Mystic
River bridge on the next AM. The radio was almost unusable on the bridge
due to the signal bouncing in & out.

We had our work cut out for us. That was in March. Later in April we drove
the radio down around the Fenway area, (Yes, That Fenway) after the tree
leaves came out. Whoops! Until we changed a circuit we almost didn't have a
product.


Jim Ussailis



Original email:
-----------------
From: Linda Taylor lintaylor at verizon.net
Date: Sun, 19 Jan 2014 12:06:01 -0500
To: Hidden-discuss at lists.hidden-tech.net
Subject: [Hidden-tech] Weird interference with TV reception


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