Chris, I use a great software package, "CommShop for Windows," which includes a program to calculate rough isolation requirements. Such programs can only provide a ballpark figure, because the results can vary a lot due to broadband noise from the PA or the degree of selectivity in the receiver, among several factors. After plugging in the values of 50 watts at 53.450 MHz for TX and 0.3 uV at 51.750 MHz for RX, I came up with 79.46 dB of isolation required. This can be met with two antennas separated 306 feet vertically, or separated 22,307 feet horizontally. You did not specify the receiver sensitivity, so I simply assumed 0.3 uV. If you're willing to accept some desense, you can get by with less isolation. I consider 80 dB of duplexer isolation to be a minimum, and prefer to achieve 95 dB or more for most repeaters.
73, Eric Lemmon WB6FLY -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of phrijjid Sent: Friday, April 03, 2009 7:41 AM To: [email protected] Subject: [Repeater-Builder] Isolation Curves I thought I "ran across" a page with isolation curves on it, i.e., isolation needed at given separation and given frequencies. Maybe just my imagination. I'm interested in isolation needed for 50 watt tx output @ 53.45 with rx @ 1.7 MHz split Thanks Chris kb0wlf
