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

On Jul 23, 4:13 pm, "Jerry Martes" wrote:
"szilagyic" wrote in message

ups.com...



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

oups.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

Hi Jerry,

I have the preamp connected to send the signal from the two antennas
down a length of coax and to a 4-way splitter that will supply a few
receivers. When I have everything hooked up except for the second
antenna, it works out well.

What would be your guestimation on how far apart the two antennas
should be, if we put them back to back???

Thank you!!
--
Chris

"szilagyic" wrote in message
ups.com...
On Jul 23, 4:13 pm, "Jerry Martes" wrote:
"szilagyic" wrote in message

ups.com...



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

oups.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

Hi Jerry,

I have the preamp connected to send the signal from the two antennas
down a length of coax and to a 4-way splitter that will supply a few
receivers. When I have everything hooked up except for the second
antenna, it works out well.

What would be your guestimation on how far apart the two antennas
should be, if we put them back to back???

Thank you!!
--
Chris

Hi Chris

I am no expert on TV and FM antennas. I do have some experience with
signal splitters and combiners.
It just seems logical that you will get the best antenna performance by
mounting them "back to back" and as far apart as you can without making a
BigJob of it.
As I understand the system connections you are using, both antennas are
being fed from one amplifier thru a signal splitter. That will be as
though you have one antenna thats physically two antennas fed in parallel
with a phase lead or lag dependent on the lengths of their coax. If both
antennas are well matched, the receiver's signal would drop 3 dB when the
second antenna is connected thru that "Signal Splitter", even if the
radiation pattern wasnt effected by that second antenna.

I think you have a very interesting project here. I also think you will
be lucky to solve the "sometimes weak signal" problem using the components
you now have.

How long is the coax and what kind is it?

Jerry

On Jul 23, 8:23 pm, "Jerry Martes" wrote:
"szilagyic" wrote in message

ups.com...



On Jul 23, 4:13 pm, "Jerry Martes" wrote:
"szilagyic" wrote in message

roups.com...

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

oups.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

Hi Jerry,

I have the preamp connected to send the signal from the two antennas
down a length of coax and to a 4-way splitter that will supply a few
receivers. When I have everything hooked up except for the second
antenna, it works out well.

What would be your guestimation on how far apart the two antennas
should be, if we put them back to back???

Thank you!!
--
Chris

Hi Chris

I am no expert on TV and FM antennas. I do have some experience with
signal splitters and combiners.
It just seems logical that you will get the best antenna performance by
mounting them "back to back" and as far apart as you can without making a
BigJob of it.
As I understand the system connections you are using, both antennas are
being fed from one amplifier thru a signal splitter. That will be as
though you have one antenna thats physically two antennas fed in parallel
with a phase lead or lag dependent on the lengths of their coax. If both
antennas are well matched, the receiver's signal would drop 3 dB when the
second antenna is connected thru that "Signal Splitter", even if the
radiation pattern wasnt effected by that second antenna.

I think you have a very interesting project here. I also think you will
be lucky to solve the "sometimes weak signal" problem using the components
you now have.

How long is the coax and what kind is it?

Jerry

We will see what happens, I'll be sure to post the results. I am
still debating whether I need a better combiner or if they are pretty
universal for quality.

The coax from both antennas to the combiner is 6 ft RG-6, with the
combiner attached to the preamp with a coupler. Then from the preamp
to the 4-way splitter is about 15 ft of RG-6 QS + 20 ft RG-6. From
the 4-way splitter to each device is about 15-20 ft RG-6.

--
Chris

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