On 3/11/2015 6:02 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 an
tenna 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.

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Tom Horne W3TDH


Tom,

There are a number of good antennas around. The problem is not going to
be the antenna, though - it will be separating the two radios. If you
transmit on one while both are connected to the antenna, you'll blow the
front end of the other.

You'll need either a coax switch/relay or some kind of filters to ensure
one does not get into the other. And even though we're talking VHF and
UHF, good filers which will provide the separation you need yet not
degrade the signal you want are expensive. If you're only talking one
frequency, maybe a couple of sets of duplexers will work - one set for
each band.

Of course, rf detecting coax switches will work - but you also then need
to ensure that both don't try to transmit at the same time - one or both
will be transmitting into an open circuit (depending on how you wire
them up).

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Jerry, AI0K

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