Antenna separation

[JamesBrox]

I was listening to a conversation about the distance needed for separation between two antennas for RX and TX on a repeater without a duplexer. The conversation was on a GMRS channel. So, let's say for an example there's a 650 repeater..... what's the proper separation between the 467.650 and the 462.650 antennas or a calculator page I can go to? Thanks

James WRXU693

 

[ecps92]

You need to add to your thoughts, not only just your repeater, but what other Transmitters are at the site.
You would be best to look into a Duplexer

Usually 2-3 Feet of Vertical separation, but other factors can come into play.
How good is the repeaters RX and how it handles overload.

 

[WA0CBW]

According to the Motorola Technical data sheets using half-wave dipole antennas you need about 25 feet vertical and 500 feet horizontal separation to get 70 db of isolation. The Decibel Products Engineering notes have the same chart.
Bill

 

[prcguy]

You would generally need a band pass cavity on the transmitter and receiver even with vertical antenna separation. Many transmitters spew out some broad band noise that lands on the receive frequency, especially in a budget setup using cheap radios. Many years ago I played with split antennas and no band pass cavities on a repeater and it just never worked out, there was always some desense.