Christopher, According to my CommShop program, a 144 MHz repeater with a 50 watt transmitter and a receiver having 0.3 uV sensitivity will require around 90 dB of isolation to avoid desense with a typical receiver. That isolation can be achieved with about 220 feet of vertical separation or about 21,300 feet (four miles!) of horizontal separation. I made the assumption that you're planning a 2m repeater, which has only 600 kHz of TX-RX separation. If the repeater is going to be a 70cm machine, with 5 MHz separation, the numbers are easier to swallow. With the same power level and sensitivity, a vertical separation of 40 feet or a horizontal separation of 975 feet would give the needed 72 dB isolation.
73, Eric Lemmon WB6FLY -----Original Message----- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Christopher Hodgdon Sent: Monday, April 21, 2008 7:00 PM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Antenna Question We are looking at setting up a basic (I know there is no such thing) repeater. What I need to know, if you do not have a duplexer to run your antenna through, but have two antennas, with one on the TX and one on the RX how far apart do they have to be to be able to correctly operate?
