"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