Quote:
Originally Posted by Tom W3TDH
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.
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Tom Horne W3TDH
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Tom,
You have too many of the same band antenna's concentrated in one place.
No matter how hard you try, they aren't going to play nice with each other.
I read 14 posts and no one gave an even close right answer to your question.
The answer is that you need to construct a tower, no less than 100', near your house in order to even try to do what you wish to do.
Even then, you will need feet of separation vertically in order to get the antenna's to play nice with each other.
Your SWR is going to be all messed up, because you have too many of the same antenna's in the same proximity.
The only good 6 / 2 / 70 cm antenna that I could recommend would be the Diamond v2000. This is the only antenna that I am aware of that has a decent amount of gain - if you want to call it that, along with being semi resonant on all three bands.
What you are doing is back-feeding everything that you transmit back into the receive of the front ends of all of the radios in your shack when any one radio transmits. Unless it is in your budget to replace all those radios on a semi annual schedule, you will eventually experience that each of those transceivers will eventually become deaf.
I have seen filters promoted in QST that allows two operators on two different bands to share a beam antenna with two transceivers, as long as each transceiver stays on it's band it is ok.
But there is a hell of a difference between 20 meters - 14 MHz - CW and 40 meters Phone.
Even though 70 cm is not a harmonic of 2m, and even though there is a heck of a disparity between 440 MHz and 146 MHZ there is always going to be problems when dealing with FM, and Digital modes.
I have to take your wife's side on this one!
Tell your club to go out and buy an acre of ground and put up a transmitter and a tower and put their packet and their D-Star crap on their tower, and then you can tune to their tower frequency if you so choose. You are killing not only all of your transceivers by what you are trying to do, but you are diminishing the range at which you yourself can operate...
If you can hear other repeaters / more than 20 miles away though all of that RF noise you have created, you will be lucky..
It doesn't matter if the radios are all turned on or off, as long as they are connected to the coax / antenna, they are still going to experience front end overload.