On 7 Jul 2007 11:38:12 GMT, wrote:

In alt.tv.tech.hdtv "Roger (K8RI)" wrote:

| The ones on my quadature array were a lot stronger than that. I
| finally gave up as it's too difficult to get the proper spacing from
| side to side across the entire UHF band. Besides at 90 feet I point
| them (I have one to the NW and one to the S) to the weak UHF stations
| and they do very well on the much stronger VHF.

If the desired signal is a single channel, two antennas connected 180
degrees out of phase (or flip one upside down), where they are spaced
an odd multiple wavelength from the desired source, and equadistant to
the multi-frequency side source (if there is a specific noisy source),
might do the trick.

The individual antennas I have listed above work quite well. Each has
its own coax and antenna mounted preamp. I just had problems with all
the lobes on the quadature array on some channels.

http://www.rogerhalstead.com/ham_files/Tower30.htm The UHF TV antenna
pointing to the NW is plainly visible. The one just below it pointing
straight south is just barely visible.

You might look into these antennas:

http://simplicitytool.com/mu_series_uhf_quad_array.htm

These antennas are wayyyy too close to really take advantage of using
the individual antennas as a quadature array. Regardless of their
claims for gain it can't be much more than one antenna alone. Front to
back *might* be legit and as they are so close as to perform like one
antenna they probably have only minor side lobes.

Unfortunately a company that puts big antennas that close together
makes me doubt their design criteria and performance figures.

Note how close their antennas are Vs boom length to the ones in
http://www.rogerhalstead.com/ham_files/tower21.htm and these are big
antennas.

One thing to remember when stacking antennas. A stacked pair will at
best be 3 db better than one. A quadature array (4 antennas) will at
best be 3 db better than the stacked pair or 6 db better than one.
Again that is _at_best_

Vertical stacking does not add side lobes over the single antenna
while horizontal stacking does. Horizontal stacking is also very
frequency sensitive so when covering the entire UHF band the
horizontally spaced antennas my exhibit quite different
characteristics on different channels. This is what makes building a
good quadature array that covers more than a few channels so
difficult.

http://simplicitytool.com/log%20periodic%20arrays.htm

On Jul 2, 1:49 pm, szilagyic wrote:
Hello:

I have been trying to find the answer to my question on the front-to-
back ratio onUHFantennas, and so far have been unsuccessful.

I think I understand what the front-to-back ratio is, but the specs on
my Winegard PR-8800 (8 bay bowtie) show negative front-to-back ratios
(-9 dB @ ch 14; -17 dB @ ch 32; -11 dB @ ch 50; -9 dB @ ch 69). The
"dB over reference dipole" is: 10.7 dB @ ch 14; 12 dB @ ch 32; 11 dB @
ch 50; 12.5 dB @ ch 69. How can the front-to-back ratio be negative,
and is this good or bad? I am assuming this could be bad in my case
as I would like the signal at the back of the antenna to be minimal.

I am currently trying to improve our HDTV reception. I currently have
the PR-8800 antenna in our attic hooked to a Radio Shack 30 dB mast
amp. This antenna works very well overall. But from time to time, on
a couple channels the HD signal strength will drop all the way down,
enough to drop the signal or cause break-up. I've been considering a
Winegard HD9095P or PR9032 to use in conjunction with the PR-8800
since they have a higher gain than the PR-8800, then rotate the
PR-8800 the other way to receive some different stations.

I really appreciate the help and feedback on this!!

Thanks,
--
Chris

Thanks to all for the help. I have replaced my Radio Shack 15-1109
preamp with a Winegard AP-8275 preamp (I know the recommended model in
this thread was the AP-8700, but I want to put in a splitter and feed
about 5 separate devices at some point). After doing a direct swap, I
noticed a slight improvement in signal quality. We gained about 5-10%
signal strength for HDTV feeds, and about the same for our FM
reception.

Best,
--
Chris