James, This is a gray area, where there are no pat answers. That said, my CommShop for Windows program calculated that 95 dB of isolation is needed for zero desense, and that can be achieved with 317 feet of vertical separation. This is a ballpark figure, since many assumptions are made in the program, some of which may skew the results considerably. As always, YMMV...
73, Eric Lemmon WB6FLY -----Original Message----- From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of James Adkins Sent: Friday, March 26, 2010 8:54 PM To: repeater-builder Subject: [Repeater-Builder] Question about antenna seperation We are considering installing a 2-meter repeater, standard 600 kHz spacing, with separate antennas for transmit and receive, looking at phasing together 2 DB-228's for RX and 2 DB-228's for TX and using a high-power transmitter, such as a Motorola Nucleus at 250-300w or other high-power transmitter. Does anyone have a formula or know what formula would need to be used to determine the amount of vertical separation needed to provide the isolation required for such a duplex operation? We are wanting separate TX and RX antennas because of plans to have the repeater on a platform located 1200' in the air, and heliax runs are not practicable. -- James Adkins, KB0NHX
