Antenna combiner/joiner question
 

"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

Antenna combiner/joiner question
 

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

Antenna combiner/joiner question
 

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.

Antenna combiner/joiner question
 

On Jul 23, 10:11 pm, valvejob wrote:
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.

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?

Antenna combiner/joiner question
 

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 article .com szilagyic writes:
On Jul 23, 10:11 pm, valvejob wrote:

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.

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?

Yes, it applies then, too.

You may want to look at the result for frequency cancellation with a good
spectrum analyzer.

Lacking that, and the knowledge of how to understand the results, you
may just have to try things and see how they work.

Alan

Antenna combiner/joiner question
 

In alt.tv.tech.hdtv szilagyic wrote:

| 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.

The simple resistive combiner, which can also be a splitter when wired
in reverse, intentionally loses 3db of signal as part of its simple
circuitry to be sure the impedances are matched. If the impedances are
not matched, things get worse because the joint becomes a point where
signals can be reflected, resulting in a number of signal abberations.
In addition, a combiner should also isolate the branches from each other.
The importance of having this depends on other factors in your design,
such as how well the antenna feedpoints match across the frequencies you
want to receive. You can get away with a mismatch on the source end if
the target end (amplifier) is well matched. But unless the combiner has
very high isolation, the two antennas form "ends" opposing each other on
the wire, and can result in signal reflections between them. A combiner
with 6 db isolation (very simple) will at least reduce those reflections
between antennas somewhat.

The proximity of the antennas to each other may also warp the pattern
they receive in, depending on their design, the exact distance, etc.

Even with a combiner of high isolation, when one antenna is picking up
the signal only the other antenna should (e.g. the "back lobe" in such
a case with antennas almost 180 degrees apart), that can result in two
sources of the same signal being merged. Depending on phase difference,
that can combine or cancel-out. Both can happen at different frequencies
depending on the exact length.

The ideal combiner system involves frequency isolation. That is, channel
filters only allow each channel to come from one or the other antenna.
This is common in well engineered cable headends. But these usually also
involve lots of large single channel antennas.

If one direction were VHF and the other were UHF, this would be easy as
the frequency isolation could be done via a VHF band filter and a UHF band
filter. I take it your case does not involve that.

Losing signal is almost certainly going to be a part of combining two
antennas. Larger antennas can compensate for it. Amplifiers per each
antenna may help as well (especially with reflections along the coax).
If your channels are intermingled, frequency isolation is going to be
very expensive.

Your last resort for full signal is two separate feeds to a switch.
That can be a nearby switch manually operated, or a switch on the mast
that is remotely controlled. But either way, your TV will never see
both sets of signals at the same time, and apparently most modern
digital tuner systems need to see the whole channel lineup at once on
the one RF feed. If an STB is part of your setup, you might consider
a 2nd STB for the 2nd feedline, and switch between them.

--
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
| first name lower case at ipal.net / |
|------------------------------------/-------------------------------------|

Antenna combiner/joiner question
 

"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.
...........................................

Over the past 50 years several antenna manufacturers have come up with
kluged arrangements to do what you propose. None worked, except in a few
special cases where the signals were very strong. What you need is an
antenna rotator, or a second antenna with its own feedline. When you combine
the outputs of two antennas without appropriate filters, not only is there a
chance of signal cancellation, but you will also quite likely have a severe
echo problem.

Tam

Antenna combiner/joiner question
 

Tam/WB2TT wrote:
"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.

..........................................

Over the past 50 years several antenna manufacturers have come up with
kluged arrangements to do what you propose. None worked, except in a few
special cases where the signals were very strong. What you need is an
antenna rotator, or a second antenna with its own feedline. When you combine
the outputs of two antennas without appropriate filters, not only is there a
chance of signal cancellation, but you will also quite likely have a severe
echo problem.

Tam


I wanted the same set up as you did using a Winegard HD8200P (combo) &
HD9095P (UHF). In the end I unhooked the UHF in the HD8200 and get VHF
(from the 8200) from one direction and UHF from another direction. I
could not combine the two and receive a good UHF signal. I will say that
my HD9095P does recieve one channel 180 deg from where it is pointed.
You might want to play with the UHF reflectors (try folding them down
some maybe) to get more 180 deg. signal.

Antenna combiner/joiner question
 

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

I wanted the same set up as you did using a Winegard HD8200P (combo) &
HD9095P (UHF). In the end I unhooked the UHF in the HD8200 and get VHF
(from the 8200) from one direction and UHF from another direction. I
could not combine the two and receive a good UHF signal. I will say that
my HD9095P does recieve one channel 180 deg from where it is pointed.
You might want to play with the UHF reflectors (try folding them down
some maybe) to get more 180 deg. signal.