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From: simnet@ssc-vax.UUCP (Mark R Poulson)
Newsgroups: sci.electronics
Subject: Re: TV Antennas
Summary: Gain, pattern, polarization
Keywords: Antenna TV
Message-ID: <3561@ssc-bee.ssc-vax.UUCP>
Date: 17 Dec 90 00:36:31 GMT
References: <12765@milton.u.washington.edu>
Organization: Boeing Aerospace & Electronics, Seattle WA
Lines: 67

In article <12765@milton.u.washington.edu>, amigo@milton.u.washington.edu (The Friend) writes:
> 
>      Anyone have some hints to improve TV reception from a TV Antenna?

Some things to consider:

1) Just because the station is in Bellingham doesn't mean that that's where
the antenna is. You may want to call the station and ask where their antenna is
located. Another poster mentioned that some stations are polarized differently.
In the US, almost every station is horizontally polarized (i.e. their antenna
dipoles are parallel to the ground). Check to make sure the station is NOT
vertically polarized, because if it is you should mount your antenna with its
dipoles perpendicular to the ground (which will screw up reception of all
normal horizontally polarized stations.)

2) Go sit on your roof with a TV and a short peice of coax. Loosen your
antenna and find out in which directions specific stations come in the best.
Hopefully the antenna is outside (not in the attic behind foil insulation!)
and is as high as possible. All you need is line of sight with your target
tower and they are usually pretty high. Try to find an orientation that works
for all the stations you watch. A horizontally polarized dipole will have a
reception pattern that looks like a figure 8. The higher the "gain" of your
antenna the more streached the 8 becomes (crude drawing):

				.
			       . .
Sources in here are received -.-* .
			      .   .
			      .   .
			       ._.  <- Antenna is here and looks like:
			      .   .
			      .   .		       _+_ <- UHF dipoles
			      .   .		      __|__
			       . .		     ___|___ <- VHF dipoles
				.		    ____|____

The higher gain antenna you purchased, the more difficult this becomes. Also
note that your worry about ch. 12 and 28 being opposite directions is not a
problem, but being perpendicular is. This assumes that the UHF dipoles are
oriented the same as the much longer VHF ones.  Needless to say, don't do this
in the rain, but doing it in the weather you watch in will help (i.e. cloudy,
clear (not around here!), cold,...).

If this step is impossible, you can use two antennas each with notch filters
that remove the bad stations from a given antenna. Combine the outputs with an
RF combiner (same as a passive splitter but used backwards) to give one
downlead to the TV.

3) Once you have a decent picture on the roof, connect your downlead to inside
the house. If you don't have similar reception you have:

	a) Used lousy Rat-Shack cabling (you need >400MHz bandwidth).
	b) Terminated it poorly or are using the wrong impedance cable
	    (you'd better be using 75 ohm coax (not 50 ohm!) or 300 ohm twin
	    lead).
	c) Used good cable, but may have bent it excessively, cut it, or
	    anything else you can to bad to coax...
	d) Have too weak a signal to make it over the cable (twin lead is
	    worst with loss).

Your idea of getting a book is probably the best. The Radio Amateurs Handbook
usually has a rather complete section on antennas. The above information is
from memory and I may have made a few errors, so please don't flame me if I
royally screwed something up (but corrections are welcome)!.

		Mark
		...uw-beaver!ssc-vax!simnet