My statement regarding "tuning" did not explicitly refer to the actual tuning of the duplexer, but to the matching of the TX and duplexer in combination. This can be proven if two Birds are used, one between the TX and the duplexer input and the other between the duplexer output and the antenna. In the majority of cases I have witnessed, adding a Bird between the TX and the duplexer will cause the forward power shown on the other Bird to change significantly. To avoid the misunderstanding, perhaps I should have used the term impedance match.
73, Eric Lemmon WB6FLY -----Original Message----- From: [email protected] [mailto:[EMAIL PROTECTED] On Behalf Of Jeff DePolo Sent: Friday, August 24, 2007 9:30 PM To: [email protected] Subject: RE: [Repeater-Builder] Duplexers > When you put the Bird between the TX and the duplexer, you > have changed the > length of the jumper cable, which upset the tuning. Adding a wattmeter or any other length of cable between the transmitter and the duplexer Tx input port has no effect on the tuning of the duplexer. It may change the load Z the transmitter sees, which may make the transmitter happier (or sadder) depending on the resulting Z, but in no way does it alter the tuning of the duplexer itself. Adding or removing cable lengths between the transmitter and duplexer also does not change the VSWR as seen by the transmitter (minimal cable loss effects notwithstanding). --- Jeff
