Just a couple comments on the original question of isolation. Vertical separation is much more effective than horizontal - and with a wide split you might be able to build a simple coaxial notch filter using a T and a length of coax on the receive side to help keep the transmitter out of the receiver. I remember seeing this kind of filter described in older VHF manuals. If interested in finding out more about this, let me know and I'll dig out my old copy and see if it really might be an option to help out the isolation. I've seen a couple set ups described where the transmit antenna and receive antenna were mounted base to base and the ground planes supposedly helped increase isolation - that might not work with J poles since there is no ground plane. Good luck - long term you might look for an old mobile telephone with an internal duplexer or even consider building a helical resonator for the receiver to help improve front end performance of the receiver. They aren't that hard to build and can work pretty good.
73 - Dan --- In [email protected], "Louis" <[EMAIL PROTECTED]> wrote: > > I apologize if this has been addressed previously, or even close! Do > not have a substantial amount of time to complete this research! > > Situation: An event in a remote area, one hill top is well enough > that coverage at around 10 watts VHF for the repeater could cover most > of our Aid Stations, 2 with HT's, the other 3 with Portables at 25 > watts or so, could get into the repeater! > > In the past, we have used crossband UHF in, VHF out, and it worked ok! > Except for issues with a couple of HT's not being able to cut the > input out during transmit! My goal, is to design a lite weight, low > power consumption (i.e. fewest batteries possible, as the hill top is > only assessable by hiking or horseback! > > What I have on hand: > > Single band 2m HT for receive > Single band Yaesu 2M FT2800R for transmit @ 12.5 watts! > Pair of homebrewed 2 m aluminum j-poles > > Need to acquire: > > simple controller - NHRC-2 looks workable! > batteries - based on estimated power consumption of final configuration! > > > Basically the question is: at a 2 mhz seperation (odd split) on VHF > can one get away without using duplexers (cans), utilizing separate > rx/tx antenna's, spaced about 20 ft apart! Without desense or other > issues! > > Being such a remote area, and the nearest 2 meter repeater is well > over 50 miles away, and nowhere near these frequencies - 145.500 > rx/147.500 out using a tone of 179.9, I do not see any interference > issues there! > > Observations, suggestions, and your crazy are appreciated! > > Thank You, > > K1STX >
