Difference between VHF and UHF base antennas

[rescuer]

OK folks, this is all hypothetical.

Say a water tower currently has 5 antennas installed on it, and due to this and that all the base stations/repeaters at that site were later removed except for one, however all the antennas and associated coax remained. I do know from past use that at least one antenna was connected to an MSR2000 and operated at 155.280. One other was connected to a UHF Med repeater (Med 8 I think). The others I do not know. Is there anyway to tell which coax is going to which antenna other than physically climbing the tower and ohming it out? What would happen if you hooked a VHF repeater (152 TX-157 RX) into one of the coax and hope you got the right one?

I know the licensing requirements/etc. I'm just curious if it would be a suitible/fairly cheap secondary repeater site.

Thanks,

[Tom in D.C.]

You should be able to make a pretty good guess by using a small
transmitter and a wattmetter and/or SWR bridge and checking for
reflected power, or lack of same, on each coax line vis-a-vis the
band of the transmitter you're using for the test.

[kf4sqb]

Check with some local Hams. Chances are, at least one of them has an MFJ SWR analyzer, like the MFJ259. That would be the simplest way to find out. Just hook it to the end of the coax/hardline, and tune it until the SWR bottoms out, then read the resonant frequency.

[tvsjr]

Any decent (likely professional) site installer/maintainer should have an antenna analyzer amidst their toys (Anritsu Sitemaster, Tektronix NetTek, etc.)... this will plot VSWR or return loss over a frequency range. Set it for a wide range and sweep each antenna, see where they are resonant. This will also tell you if you have any antenna/feedline problems (coax shorted, antenna not connected, etc.)

[mike m]

If you can't get your grubby hands on any of the fancy analyzers mentioned above, just take a VHF scanner and set it to receive a very distant Weather service frequency and then connect it to each respective antenna.

Even though the VHF antenna and phasing line may not be optimal at 162.XXX MHz it will still work better than the UHF one, I've done this in a pinch and it worked fine.

Of course if you don't have scanner then your SOL.