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

In alt.tv.tech.hdtv szilagyic wrote:

| 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.

The simple resistive combiner, which can also be a splitter when wired
in reverse, intentionally loses 3db of signal as part of its simple
circuitry to be sure the impedances are matched. If the impedances are
not matched, things get worse because the joint becomes a point where
signals can be reflected, resulting in a number of signal abberations.
In addition, a combiner should also isolate the branches from each other.
The importance of having this depends on other factors in your design,
such as how well the antenna feedpoints match across the frequencies you
want to receive. You can get away with a mismatch on the source end if
the target end (amplifier) is well matched. But unless the combiner has
very high isolation, the two antennas form "ends" opposing each other on
the wire, and can result in signal reflections between them. A combiner
with 6 db isolation (very simple) will at least reduce those reflections
between antennas somewhat.

The proximity of the antennas to each other may also warp the pattern
they receive in, depending on their design, the exact distance, etc.

Even with a combiner of high isolation, when one antenna is picking up
the signal only the other antenna should (e.g. the "back lobe" in such
a case with antennas almost 180 degrees apart), that can result in two
sources of the same signal being merged. Depending on phase difference,
that can combine or cancel-out. Both can happen at different frequencies
depending on the exact length.

The ideal combiner system involves frequency isolation. That is, channel
filters only allow each channel to come from one or the other antenna.
This is common in well engineered cable headends. But these usually also
involve lots of large single channel antennas.

If one direction were VHF and the other were UHF, this would be easy as
the frequency isolation could be done via a VHF band filter and a UHF band
filter. I take it your case does not involve that.

Losing signal is almost certainly going to be a part of combining two
antennas. Larger antennas can compensate for it. Amplifiers per each
antenna may help as well (especially with reflections along the coax).
If your channels are intermingled, frequency isolation is going to be
very expensive.

Your last resort for full signal is two separate feeds to a switch.
That can be a nearby switch manually operated, or a switch on the mast
that is remotely controlled. But either way, your TV will never see
both sets of signals at the same time, and apparently most modern
digital tuner systems need to see the whole channel lineup at once on
the one RF feed. If an STB is part of your setup, you might consider
a 2nd STB for the 2nd feedline, and switch between them.

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

"szilagyic" wrote in message
oups.com...
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.
...........................................

Over the past 50 years several antenna manufacturers have come up with
kluged arrangements to do what you propose. None worked, except in a few
special cases where the signals were very strong. What you need is an
antenna rotator, or a second antenna with its own feedline. When you combine
the outputs of two antennas without appropriate filters, not only is there a
chance of signal cancellation, but you will also quite likely have a severe
echo problem.

Tam

Tam/WB2TT wrote:
"szilagyic" wrote in message
oups.com...

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.

..........................................

Over the past 50 years several antenna manufacturers have come up with
kluged arrangements to do what you propose. None worked, except in a few
special cases where the signals were very strong. What you need is an
antenna rotator, or a second antenna with its own feedline. When you combine
the outputs of two antennas without appropriate filters, not only is there a
chance of signal cancellation, but you will also quite likely have a severe
echo problem.

Tam


I wanted the same set up as you did using a Winegard HD8200P (combo) &
HD9095P (UHF). In the end I unhooked the UHF in the HD8200 and get VHF
(from the 8200) from one direction and UHF from another direction. I
could not combine the two and receive a good UHF signal. I will say that
my HD9095P does recieve one channel 180 deg from where it is pointed.
You might want to play with the UHF reflectors (try folding them down
some maybe) to get more 180 deg. signal.

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,
--
Chris

I wanted the same set up as you did using a Winegard HD8200P (combo) &
HD9095P (UHF). In the end I unhooked the UHF in the HD8200 and get VHF
(from the 8200) from one direction and UHF from another direction. I
could not combine the two and receive a good UHF signal. I will say that
my HD9095P does recieve one channel 180 deg from where it is pointed.
You might want to play with the UHF reflectors (try folding them down
some maybe) to get more 180 deg. signal.

On Jul 23, 10:27 am, 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,
--
Chris

The problem is phasing of the signals at the combiner. You only need
to lengthen one feedline
from one source prior to the combiner, this will be done by
experiment. You could also shorten feedline a little at a time and
observe the changing signal levels. You will not get them perfect (due
to slightly different frequencies/wavelenghts). You will also effect
the impedance 'coupling' slightly which may work in your favor.