Well, one thing for darn sure - those 2 radios sharing the antenna should be
able to hear each other really really good - (till they destroy each other's
front end.)
Given the parameters (sharing some of the same frequencies) - the only way
to share the antenna is by unplugging the coax from one radio and pluggin it
into the other. - Or using a good coax switch - (which could conceivably be
a relay)
But I may be wrong.
My 2¢
w4pmj
Hal


"Big Nose" wrote in message
oups.com...
Currently I am looking into the problem of using a common antenna for
two VHF transceivers. One operates 30 - 90 MHz and the other from 30 -
512 MHz. They would both be tuned into seperate frequencies and need
to share a common broadband, omni directional, vertical monopole.

I think I am getting myself a bit confused (or should I say more
confused), do I need to used a diplexer? Would a T piece not suffice
as both sets would be tuned to different frequencies and seperation and
harmonics would be considered? Would these factors not mean that the
input impedance to the set tuned into the different frequency would
remain high thus not effect matching?