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

Since both antennas cover UHF, point in opposite directions, and are spaced
within a fraction of a wavelength at UHF frequencies and below, it is
extremely likely that the phase cancellations of the two antennas causes the
drop in signal strength when mixed in a combiner. The solutions are far as I
can tell would be to bring both feed lines (coax lines) down to the receiver
and switch when you need one or the other, or to filter out UHF content from
the log periodic with a step low pass filter, or separate the 2 antennas
more, since you appear to be creating a phased array even though you never
intended to by the way you are configuring them. Phased arrays deliberately
add and subtract RF energy to gain directivity at the expense of attenuation
in other directions.

Smarty


"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. 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

On Jul 23, 10:42 am, "Smarty" wrote:
Since both antennas cover UHF, point in opposite directions, and are spaced
within a fraction of a wavelength at UHF frequencies and below, it is
extremely likely that the phase cancellations of the two antennas causes the
drop in signal strength when mixed in a combiner. The solutions are far as I
can tell would be to bring both feed lines (coax lines) down to the receiver
and switch when you need one or the other, or to filter out UHF content from
the log periodic with a step low pass filter, or separate the 2 antennas
more, since you appear to be creating a phased array even though you never
intended to by the way you are configuring them. Phased arrays deliberately
add and subtract RF energy to gain directivity at the expense of attenuation
in other directions.

Smarty


Thanks for the quick reply. Right now the best alternative is the
spacing as I only have one downfeed that uses a preamp. What would be
the minimum distance between the two antennas that I should use, or is
it better to stack these instead, and if so what would be the minimum
distance that should be used? Or, would a metal barrier between the
two fix this issue with spacing??

I really appreciate the help.
--
Chris

On Jul 23, 10:42 am, "Smarty" wrote:
Since both antennas cover UHF, point in opposite directions, and are spaced
within a fraction of a wavelength at UHF frequencies and below, it is
extremely likely that the phase cancellations of the two antennas causes the
drop in signal strength when mixed in a combiner. The solutions are far as I
can tell would be to bring both feed lines (coax lines) down to the receiver
and switch when you need one or the other, or to filter out UHF content from
the log periodic with a step low pass filter, or separate the 2 antennas
more, since you appear to be creating a phased array even though you never
intended to by the way you are configuring them. Phased arrays deliberately
add and subtract RF energy to gain directivity at the expense of attenuation
in other directions.

Smarty




Thanks for the quick reply. Right now the best alternative is the
spacing as I only have one downfeed that uses a preamp. What would be
the minimum distance between the two antennas that I should use for
UHF considering VHF doesn't appear to be a problem, or is
it better to stack these instead, and if so what would be the minimum
distance that should be used? Or, would a metal barrier between the
two fix this issue with spacing??

I really appreciate the help.
--
Chris

"szilagyic" wrote in message
ps.com...
On Jul 23, 10:42 am, "Smarty" wrote:
Since both antennas cover UHF, point in opposite directions, and are
spaced
within a fraction of a wavelength at UHF frequencies and below, it is
extremely likely that the phase cancellations of the two antennas causes
the
drop in signal strength when mixed in a combiner. The solutions are far
as I
can tell would be to bring both feed lines (coax lines) down to the
receiver
and switch when you need one or the other, or to filter out UHF content
from
the log periodic with a step low pass filter, or separate the 2 antennas
more, since you appear to be creating a phased array even though you
never
intended to by the way you are configuring them. Phased arrays
deliberately
add and subtract RF energy to gain directivity at the expense of
attenuation
in other directions.

Smarty




Thanks for the quick reply. Right now the best alternative is the
spacing as I only have one downfeed that uses a preamp. What would be
the minimum distance between the two antennas that I should use for
UHF considering VHF doesn't appear to be a problem, or is
it better to stack these instead, and if so what would be the minimum
distance that should be used? Or, would a metal barrier between the
two fix this issue with spacing??

I really appreciate the help.
--
Chris


Hi Chris

Is there a reason for not mounting the two antennas "back to back"?
Is there an amplifier at one antenna *before* the combiner? If so, why?

Jerry

On Jul 23, 2:28 pm, "Jerry Martes" wrote:
"szilagyic" wrote in message

ps.com...



On Jul 23, 10:42 am, "Smarty" wrote:
Since both antennas cover UHF, point in opposite directions, and are
spaced
within a fraction of a wavelength at UHF frequencies and below, it is
extremely likely that the phase cancellations of the two antennas causes
the
drop in signal strength when mixed in a combiner. The solutions are far
as I
can tell would be to bring both feed lines (coax lines) down to the
receiver
and switch when you need one or the other, or to filter out UHF content
from
the log periodic with a step low pass filter, or separate the 2 antennas
more, since you appear to be creating a phased array even though you
never
intended to by the way you are configuring them. Phased arrays
deliberately
add and subtract RF energy to gain directivity at the expense of
attenuation
in other directions.

Smarty

Thanks for the quick reply. Right now the best alternative is the
spacing as I only have one downfeed that uses a preamp. What would be
the minimum distance between the two antennas that I should use for
UHF considering VHF doesn't appear to be a problem, or is
it better to stack these instead, and if so what would be the minimum
distance that should be used? Or, would a metal barrier between the
two fix this issue with spacing??

I really appreciate the help.
--
Chris

Hi Chris

Is there a reason for not mounting the two antennas "back to back"?
Is there an amplifier at one antenna *before* the combiner? If so, why?

Jerry

Hi Jerry,

It would be difficult for me to mount them back to back based on the
space where they are mounted, but if this would help our situation
then I'd be open to trying it.

There is not an amplifier before the combiner. Basically, I have the
coax feeds running directly from each antenna to the combiner, which
goes to the preamp, which runs down to a splitter, and then to a
couple receivers.

Thank you!
--
Chris

"szilagyic" wrote in message
ups.com...
On Jul 23, 2:28 pm, "Jerry Martes" wrote:
"szilagyic" wrote in message

ps.com...



On Jul 23, 10:42 am, "Smarty" wrote:
Since both antennas cover UHF, point in opposite directions, and are
spaced
within a fraction of a wavelength at UHF frequencies and below, it is
extremely likely that the phase cancellations of the two antennas
causes
the
drop in signal strength when mixed in a combiner. The solutions are
far
as I
can tell would be to bring both feed lines (coax lines) down to the
receiver
and switch when you need one or the other, or to filter out UHF
content
from
the log periodic with a step low pass filter, or separate the 2
antennas
more, since you appear to be creating a phased array even though you
never
intended to by the way you are configuring them. Phased arrays
deliberately
add and subtract RF energy to gain directivity at the expense of
attenuation
in other directions.

Smarty

Thanks for the quick reply. Right now the best alternative is the
spacing as I only have one downfeed that uses a preamp. What would be
the minimum distance between the two antennas that I should use for
UHF considering VHF doesn't appear to be a problem, or is
it better to stack these instead, and if so what would be the minimum
distance that should be used? Or, would a metal barrier between the
two fix this issue with spacing??

I really appreciate the help.
--
Chris

Hi Chris

Is there a reason for not mounting the two antennas "back to back"?
Is there an amplifier at one antenna *before* the combiner? If so,
why?

Jerry

Hi Jerry,

It would be difficult for me to mount them back to back based on the
space where they are mounted, but if this would help our situation
then I'd be open to trying it.

There is not an amplifier before the combiner. Basically, I have the
coax feeds running directly from each antenna to the combiner, which
goes to the preamp, which runs down to a splitter, and then to a
couple receivers.

Thank you!
--
Chris


Hi Chris

The best way to mount your two antennas sure would be to locate each in
the region of least sensitivity of the other. That will afford the least
amount of influence of one to the other.

As I understand it, you have an amplifier that is common to both antennas.
You probably have a good reason for doing that. But, why is the amplifier
neded between the antenna and the receiver. It appears that you now have
"one antenna" that is made in two parts. And there is an amplifier
somewhere between the antenna and the receivers.

Jerry

Stacking the antennas vertically could work but will create some nulls /
signal attenuation /cancellation in the elevation plane (versus your current
problem in the azimuth plane). The elevation nulls can put some signals near
the horizon (where you want the antenna to provide its' gain) into a deep
trough. The effect would depend on frequency / channel, the physical spacing
of the two vertically stacked antennas, and the antenna designs themselves.
To get a rough idea about how to avoid these effects either in vertical or
horizontal separation of the two antennas, consider that 1 wavelength at the
end of the UHF band is very roughly 1 meter long and that it is roughly half
that at the high end of the UHF band. A minimum separation of quite a few
wavelengths is required before the so-called "near field" effects of the
antenna diminish, and I would guess that 10 wavelength = ten meters = about
35 feet would be very adequate for low band UHF and about 17 or 18 foot
separation if you were seeing cancellation / attenuation at the high end of
the UHF band only. I would NEVER suggest putting metal / insulating plates
or surfaces between the 2 antennas since this would act as yet another
element to cause attenuation / reflections / etc.

You are therefore left the options of spatially separating the antennas on a
single mast vertically 17-35 feet apart, or on 2 masts 17 to 35 feet apart.

My approach is very conservative and somewhat smaller spacings may work
adequately, but this could only be determined by experimentation. A lot has
to do with the specific antenna designs, the arrival angles of the desired
channels / signals, the coax line lengths and impedance matches, etc., etc.,
etc.


Smarty



"szilagyic" wrote in message
ps.com...
On Jul 23, 10:42 am, "Smarty" wrote:
Since both antennas cover UHF, point in opposite directions, and are
spaced
within a fraction of a wavelength at UHF frequencies and below, it is
extremely likely that the phase cancellations of the two antennas causes
the
drop in signal strength when mixed in a combiner. The solutions are far
as I
can tell would be to bring both feed lines (coax lines) down to the
receiver
and switch when you need one or the other, or to filter out UHF content
from
the log periodic with a step low pass filter, or separate the 2 antennas
more, since you appear to be creating a phased array even though you
never
intended to by the way you are configuring them. Phased arrays
deliberately
add and subtract RF energy to gain directivity at the expense of
attenuation
in other directions.

Smarty




Thanks for the quick reply. Right now the best alternative is the
spacing as I only have one downfeed that uses a preamp. What would be
the minimum distance between the two antennas that I should use for
UHF considering VHF doesn't appear to be a problem, or is
it better to stack these instead, and if so what would be the minimum
distance that should be used? Or, would a metal barrier between the
two fix this issue with spacing??

I really appreciate the help.
--
Chris

On Mon, 23 Jul 2007 14:27:48 -0000, szilagyic
wrote:

I really appreciate all of the help and feedback.

Basically, the combiners only work with antennas (lines) that address
different frequencies.

I'm sure with the right filters and spacing you could combine things
in phase, and also instantly detect missile launches from North Korea,
but basically you want to run them down separately and put some kind
of manual switch between the two sources.

.... unless someone can point me to a source of filters that would let
him (and me!) combine things on a channel-by-channel basis, ... at
reasonable cost.

J.

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.