IIRC the Bird manual had a chart in the back for making up 1/2 wavelength coax lines (Bird + coax = 1/2 wl). If this combination is inserted on the input side of the duplexer then the measurement should be fairly correct. Other lengths "could" give other readings.
My guess would be a cable problem. Milt N3LTQ ----- Original Message ----- From: "Eric Lemmon" <[EMAIL PROTECTED]> To: <Repeater-Builder@yahoogroups.com> Sent: Saturday, August 25, 2007 1:38 AM Subject: RE: [Repeater-Builder] Duplexers > 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: Repeater-Builder@yahoogroups.com > [mailto:[EMAIL PROTECTED] On Behalf Of Jeff DePolo > Sent: Friday, August 24, 2007 9:30 PM > To: Repeater-Builder@yahoogroups.com > 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 > > > > > > > > Yahoo! Groups Links > > >
