If two close frequency transmitters are only 45 KHz 
You could use a hybrid tx combiner, but it has 3dB power 
loss per transmitter.  Sometimes you don't have the option
of two antennas at some repeater sites. One antenna with 
both radios would work but two antennas would be the more 
practical method. 

Dual antennas would allow you to pipe a single tx output to 
each...  If you were crafty, you'd use the highest antennae 
for both receivers.

Java time...!   (decafe actually) 

> At 4/5/2006 07:27, you wrote:
> >How close, frequency spacing wise, can a couple of VHF 
> >(2 meter) repeaters in the same equipment room on the 
> >same short tower be made to work well without much 
> >trouble or extra expense? How does 45 Kc. with same 600 Kc. 
> >offset sound? What will work this close and what won't?
> If the offset is the same, closer is actually better since 
> the duplexer of each repeater will protect each RX from 
> both TXs, both in RX notching of TX & TX noise suppression 
> at the RX freq.  However, isolators on both TXs are a MUST, 
> otherwise you will 2A-B mix in both TXs & end up TXing 45 kHz 
> above & below your two outputs. Try to keep the two antennas 
> as far apart as possible.  If you can't separate the antennas 
> much, you might need dual isolators on both TXs. I've seen 
> two TXs 20 kHz apart at the same site mix strong enough to be 
> heard 10 miles away, even though both systems had 
> single isolators.
> When dealing with close-freq. TX spacing, equipment shielding 
> seems to be more important for some reason.  Stay away from 
> converted mobiles as repeaters, or plan on using a separate 
> RX in an RF-tight box with EMI  feedthroughs.
> Bob NO6B

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