wrote in message
...
Dear John,

Stacking 2 HD6065P antennas in the same direction for gain you would mount
them 72" apart vertically from boom to boom. The phasing line will be 52"
long each +/- 1/8" of each other in length. The phasing lines will feed a
CC-7870 coupler to combine the signals. Your single output is now you
signal.

Cordially,
Hans Rabong
Tech. Service Manager.
Winegard Company

Unless I am missing something, seems like a waste of antenna and money.

I looked for the coupler and found this:

"You have the CC-7870 hooked up properly. However this coupler is just like
a 2-way splitter hooked up in reverse; in that it will reduce the signal
from each antenna by about 30%. "

If it is just a 2 way splitter in reverse, there is usually a 3 db loss and
all you get with 2 antennas is a gain of 3 db, so you gain nothing over a
single antenna with this coupler.

To get close to 3 db of gain you need to have a combiner of near zero loss.
This is often done by using an odd number of wavelenghts of feedline of a
differant impedance and hooking them in parallel to keep the impedance the
same. I doubt it would work very well over the while FM band,but may for a
small portion of it.

I don't know how big the antenna is, but you would be beter off with a
single larger antenna, or possiably an amplifier.
Maybe an even beter feedline.



---
This email is free from viruses and malware because avast! Antivirus protection is active.
http://www.avast.com

On Sat, 4 Jan 2014 11:14:23 -0500, "Ralph Mowery"
wrote:


Unless I am missing something, seems like a waste of antenna and money.

Nope. Stacking antennas works.

Analysis of the HD-6066P antenna.
http://www.ham-radio.com/k6sti/hd6065p.htm

"You have the CC-7870 hooked up properly. However this coupler is just like
a 2-way splitter hooked up in reverse; in that it will reduce the signal
from each antenna by about 30%. "

Since when do we measure signal levels in percent? Decibels would be
nice.
http://www.solidsignal.com/pview.asp?p=cc7870&d=winegard-cc-7870-2-way-tv-antenna-joiner-coupler-(cc7870)

If it is just a 2 way splitter in reverse, there is usually a 3 db loss and
all you get with 2 antennas is a gain of 3 db, so you gain nothing over a
single antenna with this coupler.

Nope. Let's pretend for a moment that there's no loss in the
splitter/coupler. If you feed a signal into the common (output) port,
the RF power is split equally between the other two (input) ports for
a -3dB loss per port.

However, if you feed a signal into either ONE of the two (input)
ports, all of the signal will appear on the common (output) port.
That's because there's about 20dB of isolation between the two (input)
ports so that no RF is lost going out the other (input) port.

If you have the same signal (in phase) going into both the two (input)
ports, they add, producing a combined signal 3dB higher.

However, reality requires that the combiner has some loss. Usually,
that's about -0.5dB per (input) port for a total loss of 1dB. So,
instead of 3dB gain with the stacking arrangement, you will see about
2dB gain. The -0.5dB loss varies across the band and tends to be
higher at the extreme frequencies, and less in the middle.

To get close to 3 db of gain you need to have a combiner of near zero loss.
This is often done by using an odd number of wavelenghts of feedline of a
differant impedance and hooking them in parallel to keep the impedance the
same. I doubt it would work very well over the while FM band,but may for a
small portion of it.

Yep. That's the problem. The splitter/combiner is a broadband
device, that will work over the entire TV band. 5-1000 MHz is common.
Not so if you remove the splitter/combiner and simply parallel the
phasing lines. That's a narrow band device that works over a narrow
frequency range determined by the length of the phasing lines. That's
not what you would want with a TV antenna.

However, the HD-6065P is a FM band only Yagi, which might work without
the splitter combiner, but as you mention, probably will not work over
the entire FM band.

I don't know how big the antenna is, but you would be beter off with a
single larger antenna, or possiably an amplifier.
Maybe an even beter feedline.

If you use a Yagi antenna, you would need to approximately double the
length of the boom in order to obtain an additional 3dB of gain. The
boom on the HD-6065P is 128 inches long. I would hate to see a
similar antenna with a boom twice as long.

Yagi antennas also tend to be more narrow band than Gray Hoverman
antennas for TV use. For FM band only, gain is more important, so a
Yagi is probably best. For TV, I prefer a Gray Hoverman.

Incidentally, for TV, you can compare the characteristics between both
types for real antennas at:
http://www.hdtvprimer.com/ANTENNAS/types.html
http://www.hdtvprimer.com/ANTENNAS/comparing.html
http://www.hdtvprimer.com/antennas/temporarypage.html


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

"Jeff Liebermann" wrote in message
...
On Sat, 4 Jan 2014 11:14:23 -0500, "Ralph Mowery"
wrote:


Unless I am missing something, seems like a waste of antenna and money.

Nope. Stacking antennas works.

Analysis of the HD-6066P antenna.
http://www.ham-radio.com/k6sti/hd6065p.htm

"You have the CC-7870 hooked up properly. However this coupler is just
like
a 2-way splitter hooked up in reverse; in that it will reduce the signal
from each antenna by about 30%. "

Since when do we measure signal levels in percent? Decibels would be
nice.
http://www.solidsignal.com/pview.asp?p=cc7870&d=winegard-cc-7870-2-way-tv-antenna-joiner-coupler-(cc7870)


I agree that stacking antennas works, the problem I have is the type of
combiner that is used.

The 30% was from another web site and I assume it was from someone at the
Winegard factory. Not sure why he would say 30% instead of db. Even so 30
% is nowhere near the 3.5 db listed in the ad. From the url you gave, the
spec is for 3.5 db which is around what I would think it could be if simple
resistors were used.

That combiner seems to be made not for stacking antennas for more gain, but
to combine several antennas either pointed at differant directions or so a
single feedline could be used for a TV and FM antenna or where you hae
seperate antennas on the same mast for UHF and VHF.

As the specs is for a 3.5 db loss, I assume that is if you hook up two
antennas to it, the antennas will have a gain of 3 db at the most, then you
go to the combiner and loose 3.5 db for an overall loss of .5 db.

That is where I don't see stacking two antennas and using that combiner for
more signal strength.


I do agree that to get 3 db of gain from the antenna it would need to be
about twice as long. I did not look up to antenna to see that it was about
10 feet long already. A 20 foot long antenna would be large, but so would
two antennas 10 feet long and seperated by around 5 feet.

Maybe not too bad as I have several antennas on booms that are close to 15
feet long stacked about 5 feet apart. Not the best, but it was what I could
do for what I had to work with. You can see them on my QRZ.com page under
KU4PT.




---
This email is free from viruses and malware because avast! Antivirus protection is active.
http://www.avast.com

On 1/4/2014 5:40 PM, Ralph Mowery wrote:


snip

As the specs is for a 3.5 db loss, I assume that is if you hook up two
antennas to it, the antennas will have a gain of 3 db at the most, then you
go to the combiner and loose 3.5 db for an overall loss of .5 db.

That is where I don't see stacking two antennas and using that combiner for
more signal strength.


Jeff is correct. Your error is believing the combiner has 3.5db loss.

When splitting a signal, you do have about a 3.5db loss per output,
because the signal is halved plus a bit of additional loss. However,
when combining the signals, the signal is NOT halved, so you don't have
the 3db loss there. You only have about 0.5db loss (more or less,
depending on the quality of the combiner and other factors).

Let's take an example. Since a combiner is just a splitter turned
around, we'll start with the splitter end.

Let's feed 2mw to the input of the splitter. This means each output
gets 1mw (3db loss) (we could use voltage also, but since power is
E^2/R, it's not so straightforward).

So now each leg has 1mw on it.

Now let's turn the splitter around and make it a combiner and feed two
signals, 1mw ea., same frequency, to the inputs to the combiner. Since
this is a totally passive device, the effects are reversible. If the
signals are 180 degrees out of phase, of course the output is 0.
However, if the two signals are in phase with each other, the putout is 2mw.

Note there is no 3db loss in the combiner. But of course this assumed a
"perfect" combiner, with no losses. In reality, the combiner will have
a bit of loss (typically 0.5db as noted above), so the output from the
splitter will be slightly less than 1mw and the output from the combiner
will be slightly less than 2mw.

Does this help clarify things?

And yes, phasing harnesses work the same way. The can be either
splitters or combiners, depending on how they are used. The advantage
is they have less loss; the disadvantage, as noted, is they have a much
narrower effective bandwidth.

--
==================
Remove the "x" from my email address
Jerry, AI0K

==================

"Jerry Stuckle" wrote in message
...

Jeff is correct. Your error is believing the combiner has 3.5db loss.

When splitting a signal, you do have about a 3.5db loss per output,
because the signal is halved plus a bit of additional loss. However, when
combining the signals, the signal is NOT halved, so you don't have the 3db
loss there. You only have about 0.5db loss (more or less, depending on
the quality of the combiner and other factors).

Let's take an example. Since a combiner is just a splitter turned around,
we'll start with the splitter end.

Let's feed 2mw to the input of the splitter. This means each output gets
1mw (3db loss) (we could use voltage also, but since power is E^2/R, it's
not so straightforward).

So now each leg has 1mw on it.

Now let's turn the splitter around and make it a combiner and feed two
signals, 1mw ea., same frequency, to the inputs to the combiner. Since
this is a totally passive device, the effects are reversible. If the
signals are 180 degrees out of phase, of course the output is 0. However,
if the two signals are in phase with each other, the putout is 2mw.

Note there is no 3db loss in the combiner. But of course this assumed a
"perfect" combiner, with no losses. In reality, the combiner will have a
bit of loss (typically 0.5db as noted above), so the output from the
splitter will be slightly less than 1mw and the output from the combiner
will be slightly less than 2mw.

Does this help clarify things?

And yes, phasing harnesses work the same way. The can be either splitters
or combiners, depending on how they are used. The advantage is they have
less loss; the disadvantage, as noted, is they have a much narrower
effective bandwidth.


What I am having trouble with is the 'perfect' combiner.
The one by Wineguard specs 3.5 db loss and the MiniCircuits I have specs at
3 db plus slightly more depending on frequency. I had forgotten that I
built one years ago out of the ARRL Handbook. They give it a spec of 6 db
of loss per port. The one I built has that not counting minor errors and
loss. Just checked it out.

My problem is where are you going to find a combiner for a broad frequency
that does not have any large (say over 1 db ) of loss ? Are the ones for
the TV frequencies built differant ?

For the splitters, I see the 3 db because the signal is going to two places
(3 db equals half power as we all know). But then the problem I am having
is the extra 3 db that is lossed in the combiner instead of just half of a
db or so.

Has anyone actually put one on accurate test equipment to see about the loss
like I have been trying to do ?

I understand phasing harnesses for antennas. They are almost loseless. Only
a few feet of coax worth. I have used them on antennas before. They are
not usually very broad banded unless the antennas are broad banded and made
so the impedance is not the nominal 50 ohms. That is for comercial 4 or 8
dipole arays for VHF/UHF. Lots of 'tricks' used to do that.




---
This email is free from viruses and malware because avast! Antivirus protection is active.
http://www.avast.com

On 1/4/2014 9:23 PM, Ralph Mowery wrote:

"Jerry Stuckle" wrote in message
...

Jeff is correct. Your error is believing the combiner has 3.5db loss.

When splitting a signal, you do have about a 3.5db loss per output,
because the signal is halved plus a bit of additional loss. However, when
combining the signals, the signal is NOT halved, so you don't have the 3db
loss there. You only have about 0.5db loss (more or less, depending on
the quality of the combiner and other factors).

Let's take an example. Since a combiner is just a splitter turned around,
we'll start with the splitter end.

Let's feed 2mw to the input of the splitter. This means each output gets
1mw (3db loss) (we could use voltage also, but since power is E^2/R, it's
not so straightforward).

So now each leg has 1mw on it.

Now let's turn the splitter around and make it a combiner and feed two
signals, 1mw ea., same frequency, to the inputs to the combiner. Since
this is a totally passive device, the effects are reversible. If the
signals are 180 degrees out of phase, of course the output is 0. However,
if the two signals are in phase with each other, the putout is 2mw.

Note there is no 3db loss in the combiner. But of course this assumed a
"perfect" combiner, with no losses. In reality, the combiner will have a
bit of loss (typically 0.5db as noted above), so the output from the
splitter will be slightly less than 1mw and the output from the combiner
will be slightly less than 2mw.

Does this help clarify things?

And yes, phasing harnesses work the same way. The can be either splitters
or combiners, depending on how they are used. The advantage is they have
less loss; the disadvantage, as noted, is they have a much narrower
effective bandwidth.


What I am having trouble with is the 'perfect' combiner.
The one by Wineguard specs 3.5 db loss and the MiniCircuits I have specs at
3 db plus slightly more depending on frequency. I had forgotten that I
built one years ago out of the ARRL Handbook. They give it a spec of 6 db
of loss per port. The one I built has that not counting minor errors and
loss. Just checked it out.


A perfect combiner (like anything else "perfect") doesn't exist. But it
is a very common (and handy) way of specifying how things work. It's
used all over the place in EE degree programs, for instance.

So you start with the perfect item, then add losses, phase shifts, etc.
as they occur to get a "real" part.

My problem is where are you going to find a combiner for a broad frequency
that does not have any large (say over 1 db ) of loss ? Are the ones for
the TV frequencies built differant ?


There are good combiners and bad combiners. The commercial grade ones
we use typically have 1db loss from 50Mhz to 2Ghz. Note that these
are basically splitters which are reversed to form combiners, when
necessary.

For the splitters, I see the 3 db because the signal is going to two places
(3 db equals half power as we all know). But then the problem I am having
is the extra 3 db that is lossed in the combiner instead of just half of a
db or so.


In a good quality combiner, there is no extra 3db of loss.

Has anyone actually put one on accurate test equipment to see about the loss
like I have been trying to do ?


I haven't actually measured it myself, but I do use commercial grade
splitters/combiners (not as much any more because a lot of video has
gone digital). Typical loss as a combiner is around 0.5 - 0.7 db from
50Mhz to 2Ghz.

But you also won't find these at Radio Shack or Best Buy.

And there are testing labs out there who do test these things; if any of
the ratings were off, the manufacture would quickly lose credibility in
commercial circles.

I understand phasing harnesses for antennas. They are almost loseless. Only
a few feet of coax worth. I have used them on antennas before. They are
not usually very broad banded unless the antennas are broad banded and made
so the impedance is not the nominal 50 ohms. That is for comercial 4 or 8
dipole arays for VHF/UHF. Lots of 'tricks' used to do that.


Phasing harnesses are just another form of splitter/combiner. One way
they combine; turn them around and they split. That's why they work for
both transmitting and receiving.




---
This email is free from viruses and malware because avast! Antivirus protection is active.
http://www.avast.com


--
==================
Remove the "x" from my email address
Jerry, AI0K

==================

"Jerry Stuckle" wrote in message
...
A perfect combiner (like anything else "perfect") doesn't exist. But it
is a very common (and handy) way of specifying how things work. It's used
all over the place in EE degree programs, for instance.

So you start with the perfect item, then add losses, phase shifts, etc. as
they occur to get a "real" part.



I am awear of that 'perfect' vers 'real world'. Took a 2 year asociate
degree in electronics engineering about 40 years ago. Most things are
calculated close and then trimmed to take care of the usual 5 to 10 percent
differance in components.

That is why I was not worried about anything under a DB, but just the parts
close to 3 db.



---
This email is free from viruses and malware because avast! Antivirus protection is active.
http://www.avast.com

On Sat, 4 Jan 2014 21:23:14 -0500, "Ralph Mowery"
wrote:

What I am having trouble with is the 'perfect' combiner.

I feel your pain. Many years ago, I made a similar mistake on the NEC
antenna modeling mailing list. I then processed to make a total fool
of myself and had to be corrected by the experts. Even so, I still
didn't believe it so I built a Wilkinson combiner and bench tested it
for loss. I still have the combiner somewhere as a reminder of my
mistake.

Incidentally, a Wilkinson combiner might be a tolerable solution for
combining two FM antenna. The loss is much less than a bifilar wound
toroid. I'm not sure if it will work over the entire FM band. I can
grind the numbers if anyone is interested.

My problem is where are you going to find a combiner for a broad frequency
that does not have any large (say over 1 db ) of loss ? Are the ones for
the TV frequencies built differant ?

There's only so much you can do with passive only designs. The next
step up is an active combiner:
http://www.rldrake.com/product-ac1686.php
0-3dB gain per port. 54 to 860 MHz.

Has anyone actually put one on accurate test equipment to see about the loss
like I have been trying to do ?

Yep. I have. There's very little loss between the combiner input
ports and the "sum" port. However, in the other direction, there's a
bit over 3dB loss due to the power splitting. See the specs on the
MCL splitter/combiner that you have and try it with a service monitor
or generator. Since it works down to 10 MHz, you might be able to do
the test with a function generator, a few dummy loads, some T
connectors, and an oscilloscope.

I understand phasing harnesses for antennas. They are almost loseless. Only
a few feet of coax worth. I have used them on antennas before. They are
not usually very broad banded unless the antennas are broad banded and made
so the impedance is not the nominal 50 ohms. That is for comercial 4 or 8
dipole arays for VHF/UHF. Lots of 'tricks' used to do that.

It's low, but the phasing harness loss for stacked vertical dipoles is
not zero. I've never calculated or measured it, but this might help:
http://www.kg4jjh.com/pdf/2-Meter%20Vertical%20Dipole%20Array.pdf
"The phasing harness loss at 150 MHz is calculated to be 0.67 dB."
Scaled for 100 Mhz, I would guess about 0.5 dB. Might as well use a
combiner/splitter.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

"Jeff Liebermann" wrote in message
...
On Sat, 4 Jan 2014 21:23:14 -0500, "Ralph Mowery"
wrote:

What I am having trouble with is the 'perfect' combiner.

I feel your pain. Many years ago, I made a similar mistake on the NEC
antenna modeling mailing list. I then processed to make a total fool
of myself and had to be corrected by the experts. Even so, I still
didn't believe it so I built a Wilkinson combiner and bench tested it
for loss. I still have the combiner somewhere as a reminder of my
mistake.

Incidentally, a Wilkinson combiner might be a tolerable solution for
combining two FM antenna. The loss is much less than a bifilar wound
toroid. I'm not sure if it will work over the entire FM band. I can
grind the numbers if anyone is interested.

My problem is where are you going to find a combiner for a broad
frequency
that does not have any large (say over 1 db ) of loss ? Are the ones for
the TV frequencies built differant ?

There's only so much you can do with passive only designs. The next
step up is an active combiner:
http://www.rldrake.com/product-ac1686.php
0-3dB gain per port. 54 to 860 MHz.

Has anyone actually put one on accurate test equipment to see about the
loss
like I have been trying to do ?

Yep. I have. There's very little loss between the combiner input
ports and the "sum" port. However, in the other direction, there's a
bit over 3dB loss due to the power splitting. See the specs on the
MCL splitter/combiner that you have and try it with a service monitor
or generator. Since it works down to 10 MHz, you might be able to do
the test with a function generator, a few dummy loads, some T
connectors, and an oscilloscope.

I understand phasing harnesses for antennas. They are almost loseless.
Only
a few feet of coax worth. I have used them on antennas before. They are
not usually very broad banded unless the antennas are broad banded and
made
so the impedance is not the nominal 50 ohms. That is for comercial 4 or 8
dipole arays for VHF/UHF. Lots of 'tricks' used to do that.

It's low, but the phasing harness loss for stacked vertical dipoles is
not zero. I've never calculated or measured it, but this might help:
http://www.kg4jjh.com/pdf/2-Meter%20Vertical%20Dipole%20Array.pdf
"The phasing harness loss at 150 MHz is calculated to be 0.67 dB."
Scaled for 100 Mhz, I would guess about 0.5 dB. Might as well use a
combiner/splitter.

--

I understand the idea of using 'perfect' items in electronics, then going
for more exect calculations if needed. As most electronic items are often a
5 to 10 percent variation anyway. Often you get a close calculation and
build it and trim for the desired results. I did take 2 year course in
electronics engineering about 40 years ago for an associates degree, so know
about perfect vers real components.

The Wilkinson combiner is possiable for relative narrow frequencies. Not
sure if building one out of descrete components or full size transmission
lines would be broad enough for the whole FM band either. Wild guess it
would be about the same if just two pieces of transmission line of the
correct impedance and length were used.

Isn't the Wilkinson combiner just two pieces of transmission line (or
simulated with components) with a resistor across two of the ports to
absorbe the diffeance if the loads/sources are not ballanced ? I know what
they are and have seen equipment with them in it,but never did much of a
study on it.


As the subject is combining, I have not looked into the losses of splitting,
but it would be 6 db for the simple resistor designs not counting the minor
losses. That would be 3 db for the ports and 3 db lost in the resistors.

To combind signals you would get the loss of the resistors of 3 db and a
fraction of other loss.

I am using a HP 8924C for a test set. It has just about everything you can
think of for a service monitor. Calibrated from 30 to 1000 MHz but usuable
uncalibrated to about a half of a mhz.
http://www.amtronix.com/hp8924c60.htm

As mentioned the only combiner I have is a MiniCircuits and they spec it at
3 db plus small losses depending on the frequency. That is what I am
measuring.

The diplexer/combiner will have very low loss. I have checked out 2 of them
in the past just to see and the losses were about half a db or so. However
that is for frequencies seperated by a very large percentage. Usually one
port is a low pass and the other is a high pass filter. Not suited for
signals on the same frequency as the origional poster wanted to do.

Yes, phasing harnesses on antennas are not totally loseless, but will be
mainly whatever the loss of the coax is between the elements.

If were the origional poster and there were not too many transmitters near
me, I would try a good preamp first. Mast mounted if possiable as it is for
receive only.









---
This email is free from viruses and malware because avast! Antivirus protection is active.
http://www.avast.com

On Sat, 4 Jan 2014 17:40:20 -0500, "Ralph Mowery"
wrote:

I agree that stacking antennas works, the problem I have is the type of
combiner that is used.

Well, one could always use an active combiner. For just the FM band,
that's quite easy.

The 30% was from another web site and I assume it was from someone at the
Winegard factory. Not sure why he would say 30% instead of db.

This may help explain the problem:
http://www.journalistunits.com
It doesn't include most electronic units of measure, but I think you
see the problem.

Even so 30
% is nowhere near the 3.5 db listed in the ad. From the url you gave, the
spec is for 3.5 db which is around what I would think it could be if simple
resistors were used.

Nope. A resistive combiner/splitter is -6dB.
http://www.microwaves101.com/encyclopedia/resistive_splitters.cfm
"Resistive power dividers are easy to understand, can be made
very compact, and are naturally wideband, working down to
zero frequency (DC). Their down side is that a two-way resistive
splitter suffers 10xlog(1/2) or 3.0103 dB of real resistive loss,
as opposed to a lossless splitter like a hybrid. Accounting for
3.0103 dB real loss and 3.0103 dB power split, the net power
transfer loss you will observe from input to one of two outputs
is 6.0206 dB for a two-way resistive splitter, so they are often
called 6 dB splitters. Dig?"

That combiner seems to be made not for stacking antennas for more gain, but
to combine several antennas either pointed at differant directions or so a
single feedline could be used for a TV and FM antenna or where you hae
seperate antennas on the same mast for UHF and VHF.

When one combines two different band antennas, the usual method is a
diplexer. Since the receiver only sees one antenna on each band, the
impedance is constant. A low pass filter can also be made very low
loss if you don't care much about rolloff and ripple. However, if
we're down to the point where small fractions of a dB produce a
noticeable difference, I suspect that additional gain (tower mounted
pre-amp) or less loss (better coax cable) will be more important.
Something like this:
http://www.solidsignal.com/pview.asp?p=uvsj
0.5 dB insertion loss. Oh well.

As the specs is for a 3.5 db loss, I assume that is if you hook up two
antennas to it, the antennas will have a gain of 3 db at the most, then you
go to the combiner and loose 3.5 db for an overall loss of .5 db.

Please re-read what I wrote. From each of the (input) ports to the
receiver port (output), there is only 0.5dB of loss. If two antennas
provide an additional 3dB of gain, and each port gobbles 0.5dB, then
the combined gain is 2dB.

That is where I don't see stacking two antennas and using that combiner for
more signal strength.

Would you rather make the yagi twice as long? Once we get to very
large antennas, 3dB of additional gain can easily become a mechanical
challenge.

I do agree that to get 3 db of gain from the antenna it would need to be
about twice as long. I did not look up to antenna to see that it was about
10 feet long already. A 20 foot long antenna would be large, but so would
two antennas 10 feet long and seperated by around 5 feet.

Note that FM broadcast stations with directional antennas use various
vertically mounted antennas, not Yagis. They're interested in
survivability as well as gain and pattern. A 20ft long antenna is
possible, but I don't think anyone wants to climb the tower and drop
the antenna to fix a broken element. That's much easier with a side
mounted barbeque grill type antenna, stacked dipoles, crossed dipoles,
horizontal loops, etc.

Maybe not too bad as I have several antennas on booms that are close to 15
feet long stacked about 5 feet apart. Not the best, but it was what I could
do for what I had to work with. You can see them on my QRZ.com page under
KU4PT.

You probably don't have overweight birds sitting on your yagi
elements. Yes, it can be made to work but it's so much easier and
neater to do it with a combiner.



--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558