You don't move the Invar rods at all- those are the pass adjustments. You first adjust the Invar rods for minimum insertion loss at the pass frequency, then you adjust the side rods to achieve maximum rejection at the notch frequency. Just so we're talking apples and apples, the Invar rod is in the center of the cavity, and it usually has a black knob on it.
The notch adjustment usually tracks the pass adjustment fairly well, so the quick and dirty way to get the duplexer in the ballpark is to move the center (Invar) rod in or out to achieve maximum quieting of a distant transmitter on the receive frequency. Then do the reverse to move the center rod on the transmit side, using a handheld to generate the signal. Do not use the repeater transmitter for this adjustment. Since you have eliminated the original tuning with experimentation, perhaps it would be a good idea to properly tune the duplexer with the appropriate test equipment. The tuning info is here: <www.repeater-builder.com/wacom/wp6xx-vhf-tuning-instructions.pdf> 73, Eric Lemmon WB6FLY -----Original Message----- From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of hbbcara Sent: Saturday, July 18, 2009 5:48 PM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] wp-639 -- How far should I expect to move the invar rods? Hi all, In tuning the reject for a wp-639, how far should I expect to move the invar rods to find the notch? In tuning mine (the poor man's way - system on the air receiving a weak station) I didn't find a definite place I"d call a null. There was more noise on the signal with the rod pushed most of the way in and less noise with the rod most of the way out, but it was a gradual change. I expected to find it noisy with the rod mostly in, noisy with the rod mostly out and at some point in between a quieter spot. SO my question is, should I hear a definite "noisy-quiet-noisy" pattern as I move the rods and if so, over how much motion of the rods is it likely to fall? An inch? Half-inch? Three inches? Or would that pattern only be noticeable with "the right equipment." (Some background - the duplexer is from an uncertain origin, but it has a factory sticker saying 146.97 - 146.37 with the ports marked "high input" and "low input." I'm using it on 146.88/28 so it shouldn't be an "upside-down" issue.) Thanks for any info! rj
