Allan, Several years ago, I corresponded with the designer of the CommShop for Windows program, and I posed the same question. His answer was that the calculations were based upon an average of typical commercial receivers. I suspect that the extensive research by General Electric Company in developing the "Duplex Operation Curves" (available on the GE Master LBI Index) was considered.
My personal experience is that CommShop and similar programs are likely to err on the generous side, and that more isolation will be required than predicted in order to achieve zero desense in duplex operation. 73, Eric Lemmon WB6FLY -----Original Message----- From: [email protected] [mailto:[EMAIL PROTECTED] On Behalf Of allan crites Sent: Friday, March 23, 2007 9:37 PM To: [email protected] Subject: RE: [Repeater-Builder] TX & RC antenna seperation Eric, Just what kind of receiver did you use in your ballpark estimate example? Allan Crites WA9ZZU Eric Lemmon <[EMAIL PROTECTED]> wrote: Sam, Just to give you a ballpark estimate, I used CommShop for Windows to generate a solution for a 50 watt transmitter that is separated by 600 kHz from a receiver with 0.25 uV sensitivity in the 2m Amateur band. CommShop reported that a minimum of 90.14 dB of isolation is required, which can be met with a vertical antenna separation of 240 feet- assuming that the antennas are identical and are exactly in line with each other vertically. The required horizontal separation to achieve the same isolation is about five miles, which is obviously impractical without a link radio. If you use a transmitter with greater power, or use a receiver with greater sensitivity, the required isolation and the separation will increase. It makes no difference if your machine is used once a year or continuously; the isolation requirements are firm. 73, Eric Lemmon WB6FLY -----Original Message----- From: [email protected] <mailto:Repeater-Builder%40yahoogroups.com> [mailto:[email protected] <mailto:Repeater-Builder%40yahoogroups.com> ] On Behalf Of Sam Sent: Friday, March 23, 2007 9:27 AM To: [email protected] <mailto:Repeater-Builder%40yahoogroups.com> Subject: [Repeater-Builder] TX & RC antenna seperation What would be the guidelines to use for antenna separation on a 2 meter machine w/o a duplexer. Horizontal and vertical, this will be a limited use machine, so there will not be a lot of traffic. Sam KE5MID
