On Jul 23, 10:11 pm, valvejob wrote:
On Mon, 23 Jul 2007 14:27:48 -0000, szilagyic
wrote:



Hello,

I have two antennas that I am trying to combine, and have a question
in regards to the best way to do this. The first antenna is a
Winegard HD7084P (FM/VHF/UHF lpda) that is hooked to a preamp and
tuned in perfectly. I want to add my other antenna (Winegard PR-8800
UHF bowtie) that is also tuned in and points in the opposite direction
(almost 180 degrees) to pick up some UHF stations. The two antennas
are side by side, but the ends of the elements are about 4 feet
apart. When I disconnect the HD7084P from the preamp and connect the
combiner and hook the HD7084P to the combiner, the signal strength for
HD stations maintains about the same. But when I hook up the second
antenna to the combiner, the HD signal strength from the HD7084P drops
by 10-40% (depending on the channel). I tried two combiners/splitters
and got the same results, one is a RCA brand splitter, the other is a
Radio Shack hybrid splitter/combiner. Would something like the
Channel Master 0538 or the Winegard CC-7870 work better for this?? I
read up and these models mention "high isolation" which I can't seem
to find any information on. It seems like a powered combiner would be
ideal so that there is no loss at all, but I haven't seen anything
like that. I am looking for any suggestions or ideas that anybody
might have.

I really appreciate all of the help and feedback.

Thank you very much,

When you join two antennas, the wavelengths are different for the
different channels. Some may cancel each other on your favorite
channel and some may be additive on channels you don't care about.

You can adjust the lengths of the leads going to the two antennas and
change which channels/wavelengths are additive. Try a shorter cable
on one of the two antennas.

This makes sense, but does this apply for antennas that are pointed in
opposite directions? I just want to clarify, you are basically saying
to alter the cable length by say, a portion of a wavelength (a half of
a wavelength?), for one of our favorite channels that is having issues?

In article .com szilagyic writes:
On Jul 23, 10:11 pm, valvejob wrote:

When you join two antennas, the wavelengths are different for the
different channels. Some may cancel each other on your favorite
channel and some may be additive on channels you don't care about.

You can adjust the lengths of the leads going to the two antennas and
change which channels/wavelengths are additive. Try a shorter cable
on one of the two antennas.

This makes sense, but does this apply for antennas that are pointed in
opposite directions? I just want to clarify, you are basically saying
to alter the cable length by say, a portion of a wavelength (a half of
a wavelength?), for one of our favorite channels that is having issues?

Yes, it applies then, too.

You may want to look at the result for frequency cancellation with a good
spectrum analyzer.

Lacking that, and the knowledge of how to understand the results, you
may just have to try things and see how they work.

Alan

In alt.tv.tech.hdtv szilagyic wrote:

| This makes sense, but does this apply for antennas that are pointed in
| opposite directions? I just want to clarify, you are basically saying
| to alter the cable length by say, a portion of a wavelength (a half of
| a wavelength?), for one of our favorite channels that is having issues?

No antenna perfectly eliminates the back lobe. Some just do better than
others (like a solid parabolic dish). The bow tie antenns will receive
some signal in the reverse direction. If that back lobe reception on one
combines out of phase with the front lobe of the other, it will reduce
the total sign somewhat.

--
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
| first name lower case at ipal.net / |
|------------------------------------/-------------------------------------|

On Jul 24, 7:50 pm, wrote:
In alt.tv.tech.hdtv szilagyic wrote:

| This makes sense, but does this apply for antennas that are pointed in
| opposite directions? I just want to clarify, you are basically saying
| to alter the cable length by say, a portion of a wavelength (a half of
| a wavelength?), for one of our favorite channels that is having issues?

No antenna perfectly eliminates the back lobe. Some just do better than
others (like a solid parabolic dish). The bow tie antenns will receive
some signal in the reverse direction. If that back lobe reception on one
combines out of phase with the front lobe of the other, it will reduce
the total sign somewhat.

--
|---------------------------------------/----------------------------------*|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
| first name lower case at ipal.net / |
|------------------------------------/-------------------------------------*|

Would some of these 'jointennas" reduce the interference /
interaction? They're not cheap but as much a s a cable bill.

http://www.warrenelectronics.com/ant...Jointennas.htm

Did I miss it or did nobody ask what the actual channels in question
are? Any idea of the relative signal strengths? How far away? I would
think if the antennas are "spectally separated" via diplexers, the
cable lengths woun't be all that critical. It also depends on how far
apart the channel frequencies are. If you have a 28 and 30 in front
and are trying to get a 29 from the back, that will be tough but if
it's several channel numbers apart, it is less tough. SO, what are the
channels in question?

GG

On Jul 25, 12:32 am, G-squared wrote:
On Jul 24, 7:50 pm, wrote:



In alt.tv.tech.hdtv szilagyic wrote:

| This makes sense, but does this apply for antennas that are pointed in
| opposite directions? I just want to clarify, you are basically saying
| to alter the cable length by say, a portion of a wavelength (a half of
| a wavelength?), for one of our favorite channels that is having issues?

No antenna perfectly eliminates the back lobe. Some just do better than
others (like a solid parabolic dish). The bow tie antenns will receive
some signal in the reverse direction. If that back lobe reception on one
combines out of phase with the front lobe of the other, it will reduce
the total sign somewhat.

--
|---------------------------------------/----------------------------------*|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
| first name lower case at ipal.net / |
|------------------------------------/-------------------------------------*|

Would some of these 'jointennas" reduce the interference /
interaction? They're not cheap but as much a s a cable bill.

http://www.warrenelectronics.com/ant...Jointennas.htm

Did I miss it or did nobody ask what the actual channels in question
are? Any idea of the relative signal strengths? How far away? I would
think if the antennas are "spectally separated" via diplexers, the
cable lengths woun't be all that critical. It also depends on how far
apart the channel frequencies are. If you have a 28 and 30 in front
and are trying to get a 29 from the back, that will be tough but if
it's several channel numbers apart, it is less tough. SO, what are the
channels in question?

GG

GG,

I came across those Jointennas and they look very interesting.
Unfortunately the channels (frequencies) we are trying to get are all
spread out. Here's a list anyway:

On the first antenna (VHF/UHF/FM) we get channels
2,4,7,9,20,28,50,56,62 (analog), and 14,21,41,43,44,45,52,58
(digital).

On the second antenna (UHF only) we get channels 18,23,47,53 (analog),
and 34,38,51,57,59 (digital).

Just out of curiousity, what is the average loss in dB when using the
Jointennas, or does it vary? I haven't been able to find any info on
the loss.

Thank you very much. There have been some great ideas posted in this
thread and we will try various things hopefully soon and see what
works.
--
Chris