Paul, There are many useful programs available for calculating duplexer isolation and antenna separation. I happen to like CommShop for Windows, but I know that it (like all of the other programs) makes some assumptions in the calculations.
I plugged in 25 watts for TX power, 144.000/144.600 for frequencies, and 0.3 uV for RX sensitivity. CommShop determined that the necessary isolation was about 86 dB. It also calculated that this isolation could be achieved with a vertical antenna separation of 183 feet or a horizontal antenna separation of 15,058 feet- about 2.8 miles. Needless to say, a 600 kHz split at 2m does not lend itself to separate antennas! In my area of California, the 2m coordinator (TASMA) has set aside a wide-spaced pair exclusively for portable/mobile repeater operation. The 2.655 MHz split allowed me to assemble a complete repeater in a portable case of about one cubic foot, using a Celwave 5085-1 compact duplexer. The radio is a 10-watt full-duplex Motorola R1225 transceiver, which has an internal controller and Morse ID-er. When I finish converting the prototype into the final product, I'll post some pictures. I strongly suggest that you petition your local two-meter coordinating body to establish a wide-spaced pair for short-term portable and mobile operation. 73, Eric Lemmon WB6FLY -----Original Message----- From: [email protected] [mailto:[EMAIL PROTECTED] On Behalf Of Paul Yonge Sent: Friday, January 20, 2006 9:27 PM To: [email protected] Subject: Re: [Repeater-Builder] Re: Duplexer retune / recoax All this discussion about duplexer tuning and cabling is making me wonder if I should not order a duplexer for the TKR-750 and just use separate TX and RX antennas. Most repeaters, of course, operate on a specific frequency pair but, since mine will be mobile and could be set up anywhere, I'll be selecting whichever frequency pair throughout the 2-meter band that's reserved for repeater use and won't cause any interference with a coordinated repeater wherever I stop. I'll have to be careful about being co-channel with anyone within 120 miles and avoid adjacent frequencies unless I can get the proper separation with the adjacent repeater. By using non-ground plane antennas with magnetic mounts atop the spacious roof of the Sprinter van, there's some flexibility on the spacing between the TX and RX antennas. Is there some rule of thumb for spacing these two antennas (that will be at the same height above ground)? Paul Yonge KC2PBD WQDY219 MIDLAKES REPEATER Yahoo! Groups Links Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
