On 3/11/2015 5:02 PM, Tom W3TDH wrote:
I am looking for recommendations for a dual band antenna that will
serve two 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 will be hard for SWMBO; as in Rumpole's
spouse, She Who Must Be Obeyed; to tolerate the use of both our
home's gable ends and the chimney being used to support antennas. I
am planning to replace my Diamond X-30 with a triband vertical 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
meter / Seventy Centimeter dual band vertical that I am asking for
help in selecting.

One radio will be a two meter packet node which will be used as a
Winlink Radio Message Server. The other radio will be a UHF D-STAR
hotspot. I am willing to pay what is needed to to get the best
antenna for this application but I don't want to waste money
ineffectively. So the two meter radio will 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 hotspot is
not supposed to be a terribly wide area installation I would imagine
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 Radio 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 have yet to master antenna modeling
but I would imagine; given all the warnings 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
encouragement to do something that will be ineffective. Thank you in
advance for any help you may be willing to offer.

-- Tom Horne W3TDH


Hi, Tom -

I did some quick, crude modelling of a vertically-polarized half-wave
(J-Pole) and it seems to have a pattern about as good on 70cm as on 2M.
There is a bit more energy radiated about 50 degrees above the horizon
on 70cm, but there seems to be plenty left at about 1.5 degrees (about
6.5dBi). I assumed an antenna height of 20 feet.

If it were me, I would try the J-Pole. However, you need to consider how
much time and effort it would take to change to a different antenna if
you are not happy.

73, John N1JLS