Chris,
"Back to Back" mounting only makes sense if you either can rotate the entire
array with a rotor or if the signals you are trying to receive are
coincidentally 180 degrees apart on the compass from your receiving location
using a fixed (non rotating) array. The log periodic array you are using no
doubt is highly directive, and the bow tie at UHF is, even with a reflector
element added to the UHF bowtie dipole, an asymmetrical figure eight. The
cancellation effects will still occur at UHF until you get the two antennas
physically separated, either horizontally or vertically.

The combiner and coax length / mismatch issue is far less important.

Smarty

"Jerry Martes" wrote in message
news:3Rdpi.12267$U47.3415@trnddc08...


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

Hi Chris

I'm surprised that the amplifier is needed. But, you have determined
that it does improve reception so I have nothing to add to what you have
done.
I do submit to you that the high quality splitter/combiner isnt likely to
provide you with any improvement in TV reception.
When you connect two seperate antennas to one output terminal, like with
a splitter, you then have One Antenna that has two feed points. Mount
the two antennas "back to back", and dont spend too much money on high
quality splitters.

Good luck
Jerry