Antony, For a rough approximation, one must know the following information: Transmitter frequency in MHz, Transmitter power in Watts, Receiver frequency in MHz, and Receiver sensitivity in microvolts or dBm.
As an example, let's assume that your repeater transmits at 147.300 MHz with 50 watts, and receives at 147.900 MHz with 0.3 microvolts of sensitivity. My CommShop software program estimates that about 89 dB of isolation between TX and RX is needed, and this isolation can be met with separate antennas 220 feet apart vertically or 21,782 feet apart horizontally. Obviously, horizontal separation of more than four miles is impractical unless a link radio is used. The vertical arrangement is assumed to be in line, with one antenna exactly above the other. Although vertical separation is practical when a tall tower is available, the use of Heliax or similar hardline with 100% shielding is mandatory. Keep in mind that programs such as CommShop make some assumptions about your radios that may be erroneous. YMMV... 73, Eric Lemmon WB6FLY -----Original Message----- From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of antony Sent: Sunday, August 29, 2010 2:35 AM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] ariels using two radios as a repeator with two ariels. how far appart would the ariels be best. thanks antony
