Antenna combiner/joiner question
 

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

Antenna combiner/joiner question
 

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 / |
|------------------------------------/-------------------------------------|

Antenna combiner/joiner question
 

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

Antenna combiner/joiner question
 

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

Antenna combiner/joiner question
 

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.

Antenna combiner/joiner question
 

On Jul 25, 10:44 am, DeanO wrote:
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.

The whole point of a diplexer (jointenna) is to filter out individual
channels so that 'phasing' is no longer an issue for combining the
feeds. The actual insertion loss of a jointenna should be aound 1 dB
on a pass through channel

GG