In article ,
mm wrote:

Does it matter if the tv antenna points one way, or 180^ the other?

That depends on the antenna.

Typical log-periodic rooftop TV antennas are moderately directional.
They have the greatest gain when the small end is pointing towards the
transmitter. Directly off of the back, they're usually around 10 dB
worse (i.e. one-tenth the power sensitivity). There are some
directions around the side which are going to be *extremely*
insensitive (very deep nulls).

Other sorts of antennas are bidirectional.

You'll probably get the best reception from a directional antenna,
aimed towards the transmitter (or, sometimes, aimed off at an angle
which minimizes the antenna's pickup of reflections from nearby
buildings and trees).

You guys, especially Dave, have convinced me that I need a better (and
thus bigger) antenna more than I need an amplified antenna.

That's often the case. If your signal level at the TV is low, it's
usually better to try to improve it by adding antenna gain, than it is
to use an amplifier. An amplifier will boost incoming noise by just
as much as it will boost the desired signal.

Does it
matter if I point an antenna with several elements of different
lengths to the station, or if I point it the exact opposite direction?
In my attic, it would be more convenient to do the latter. (I'm too
old and at least now, too fat to go on the roof.)

You'll lose a significant amount of sensitivity if you point a
traditional log-periodic antenna directly away from the TV station.
With a 10 dB front-to-back ratio (typical for a log-periodic) you
could cut the antenna range to about a third of what it would be at
its best.

Let me toss out another idea for you. If you've got attic space which
runs long-wise towards, and away from the TV towers, you could install
a rhombic antenna. This is simply a diamond-shaped pattern of two
wires, with the long axis of the diamond pointing towards / away from
the transmitter. The feedline to the TV attaches at one end. At the
other end, you can either "terminate" the rhombic with a resistor, or
leave the two ends of the wires unconnected.

If you terminate the antenna with a resistor, it becomes a
unidirectional antenna... the resistor is at the end pointed towards
the transmitter, and the feedline attaches at the other end.

If you leave the wires at the far end open (unconnected) the rhombic
is essentially bidirectional... it can receive signals from stations
located off of either end.

Rhombics are fairly wide-band antennas. Their impedance is such that
yu can probably use a standard 4:1 balun transformer to match them to
a 75-ohm coax.

They do take up a fair bit of space - each "arm" of the diamond needs
to be at least one wavelength long at the lowest frequency you want to
receive. The longer, the better (as far as gain goes).

A big advantage to them is that they're inexpensive... all you need is
wire, a termination resistor (450-to-600-ohm carbon composition will
do), and a balun transformer.

http://en.wikipedia.org/wiki/Rhombic_antenna has an overview.

Also, I thought 50 miles was the longest range on level ground for a
transmitting tower of typical height and an antenna on the roof of a
two-story house.

So what about a claim that a Wineguard antenna has a range of 75 to 80
miles????
http://estore.websitepros.com/112973...00U/Detail.bok

It depends very much on how high your rooftop is, and how high your
mast is, and on the nature of the terrain between you and the
transmitter. You can count on some amount of diffraction, which
can actually let your antenna "see" a TV transmitter which is below
the optical horizon.

This antenna is rated for low-band VHF and I don't need that, I've
learned, but it's the mileage claim I am asking about.

Even this one says: Up to 60 mile VHF range; 45 mile UHF range Don't
they get that by mounting it on a 100 foot tower or something?
http://www.radioshack.com/product/in...ductId=3739594

"Up to" distance numbers are probably subject to the same sort
of marketing inflation, and selective-circumstances picking that
affect fuel-economy figures for cars. I'd guess that the upper
limits of the "up to" ranges may assume a TV transmitter on top of
Mount Wilson (or a similar-sized molehill), an antenna mounted on a
tall mast on top of a multi-story apartment building, clear terrain,
and perhaps a bit of atmospheric ducting under favorable weather
conditions. "We saw a picture once, for 30 seconds, at 80 miles, so
the range is up to 80 miles!"

And isn't the info obsolete because digital transmitters are working
at lower power than analog did?

"Assumes facts not in evidence."

A lot of TV stations had to run their "transition" digital
transmitters at lower power than their analog transmitters, for any of
a number of technical and legal reasons. Many of them (perhaps most)
either boosted their digital transmission power on The Big Day (when
the analog transmitters were turned off) or are in the process of
doing so as time goes by.

TV stations *really* don't like losing area-coverage, since this
reduces the number of viewers they can claim, and reduces the value of
the commercial-ad time they have available to sell. Stations will tend
to want to push up their transmitter power as far as they can afford
and/or as far as the FCC will let them.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!