I am looking for recommendations for a dual band antenna that will serve tw
o separate radios. The reason that I want to use a single antenna is that
I have a limited number of mounting points for antennas. At present it wil
l be hard for SWMBO; as in Rumpole's spouse, She Who Must Be Obeyed; to tol
erate the use of both our home's gable ends and the chimney being used to s
upport antennas. I am planning to replace my Diamond X-30 with a triband v
ertical for Six, Two, and .7 Meters. The chimney will then support a rotor
aimed Two and .7 Meter beam. The second gable end will support the Two me
ter / Seventy Centimeter dual band vertical that I am asking for help in se
lecting.

One radio will be a two meter packet node which will be used as a Winlink R
adio Message Server. The other radio will be a UHF D-STAR hotspot. I am w
illing to pay what is needed to to get the best antenna for this applicatio
n but I don't want to waste money ineffectively. So the two meter radio wi
ll be in the 144 MHz portion of the band and I don't yet actually know were
the D-STAR hotspot will be run. I have a DCI filter and diplexer to keep
the two radios from actually knowing of each others existence. Since a hot
spot is not supposed to be a terribly wide area installation I would imagin
e that I do not want an extremely high gain antenna but I am perfectly open
to be reeducated on that. The difficulty is that I would guess that the R
adio Message Server / Packet would benefit from as much horizontal gain as
can be achieved. I have a home brewed collinear two meter J-Pole that has
been a good performer on two meters and presents a low SWR on 440 MHz. I h
ave yet to master antenna modeling but I would imagine; given all the warni
ngs I have read on line; that it has poor radiation pattern on UHF. Is it
likely to be too poor a performer for a hot spot on UHF?

I really am asking because I want to know. I am not looking for encouragem
ent to do something that will be ineffective. Thank you in advance for any
help you may be willing to offer.

--
Tom Horne W3TDH

On Sat, 14 Mar 2015 10:12:20 EDT, Tom Horne wrote:

I am looking for recommendations for a dual band antenna that will serve tw
o separate radios. The reason that I want to use a single antenna is that
I have a limited number of mounting points for antennas.

Many years ago I had a similar problem on a commercial tower. I was
paying for tower space essentially by the antenna. My boss at the
time did not want to pay for two antennas. I had to devise a scheme
that would share a single mount point. I asked if two coax cables
were acceptable, to which he agreed. So, I built a dual 5/8 wave VHF
antenna, with one antenna mounted above the mounting arm, and the
other mounted below the arm, pointing downward. Getting the isolation
right and camouflaging the fact that it was really two antennas, was
tricky. I wish I had antenna modeling software, but resorted to
optimizing by cut-n-try. Sorry, no NEC antenna models, but I may have
some photos buried somewhere.

One useful trick was to make the two coax cables the same length. The
leakage between antennas was about 1/2 wave apart, resulting in
cancellation in the respective receivers. As I vaguely recall, I had
about 12-15 dB isolation, which I consider to be quite good for such a
derangement. I don't know how dual band will work, but I suspect it
will be usable. If you have a line stretcher (or huge collection of
barrel connectors), you can test the effects of coax line length
differences.

Also, be advised that commercial antennas are designed to drain water
only in their normal mounting position. After filling the lower
antenna with water in a garden hose spray test, I had to drill a hole
in the end of the antenna to provide an exit path.

Of course, I was generating considerable intermod if both transmitters
were on at the same time, but I didn't know much about intermod at the
time making it a non-problem.

Within a few months, some of my competitors on the same mountain top
discovered my trick and cloned it (with varying degrees of success).
That worked for a few years, until the tower/building owner figured
out what was happening and began to charge by the coax cable. After
that, common receive antennas with multicouplers became the cost
saving method of choice.

Good luck and remember that with antennas, the uglier it looks, the
better it works.


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

On Sat, 14 Mar 2015 10:12:20 EDT, Tom Horne wrote:

I am looking for recommendations for a dual band antenna that will serve tw
o separate radios. The reason that I want to use a single antenna is that
I have a limited number of mounting points for antennas.

One radio will be a two meter packet node which will be used as a Winlink R
adio Message Server. The other radio will be a UHF D-STAR hotspot. I am w

At the hospital we use a tri-band (144, 222, 440) Comet vertical
antenna fed with a single coax cable, and at the radio end a three-way
splitter and a set of Polyphaser bandpass filters for each radio. That
is necessary because of the high rf environment. Has worked well for
over 10 years.

The dual-band (2m/440) equivalents are available off-the-shelf from
your favorite ham radio supplier (store or on-line).

It sure beats messing around with any of the other schemes reported
here.

73 de K2ASP - Phil Kane

Member, Washington County, OR
Emergency Communications Team
for ARES/RACES and HEARTNET

Station Co-manager - W7PSV / K7PSV
Providence St. Vincent Medical Center
Disaster Communication Team

On Sunday, March 15, 2015 at 3:59:22 PM UTC-4, Phil Kane wrote:
On Sat, 14 Mar 2015 10:12:20 EDT, Tom Horne wrote:

I am looking for recommendations for a dual band antenna that will serve
tw
o separate radios. The reason that I want to use a single antenna is th
at
I have a limited number of mounting points for antennas.

One radio will be a two meter packet node which will be used as a Winlin
k R
adio Message Server. The other radio will be a UHF D-STAR hotspot. I a
m w

At the hospital we use a tri-band (144, 222, 440) Comet vertical
antenna fed with a single coax cable, and at the radio end a three-way
splitter and a set of Polyphaser bandpass filters for each radio. That
is necessary because of the high rf environment. Has worked well for
over 10 years.

The dual-band (2m/440) equivalents are available off-the-shelf from
your favorite ham radio supplier (store or on-line).

It sure beats messing around with any of the other schemes reported
here.

73 de K2ASP - Phil Kane

Member, Washington County, OR
Emergency Communications Team
for ARES/RACES and HEARTNET

Station Co-manager - W7PSV / K7PSV
Providence St. Vincent Medical Center
Disaster Communication Team

Phil

How does the use of Polyphaser band pass filters instead of Digital Communi
cations Incorporated band pass filters make your situation different from w
hat I have been asking about here. What would be a tremendous help is for
you to provide the model numbers for the filters you are using there. That
would give us a different manufacturer to turn to for band pass filters co
upled with the knowledge that the models you are using are already working
in a very similar application.

The only difference that is obvious to me is that you appear to only need o
ne transceiver to be able to operate on each of those bands at one time wer
e on two of them I will have a need for two transmitters at the same time.
Between the vertical separation of the two multi-band antennas and the two
MHz separation of the co band operating frequencies I am hoping to make it
work.

--
Tom Horne W3TDH