Jeff, I'll be the first to admit that reality often contradicts theory. However, both EMR and TX-RX have published application notes which support my statement.
Some time ago, I tried to tune up a Sinclair Q-202G BpBr duplexer for a Ham, which simply involved moving from one 2m pair to another pair only 120 kHz away. The label on the duplexer showed that it was originally made for a 600 kHz split in the 2m band, but I was unable to get the insertion loss below 3.0 dB, even though each cavity had the correct 0.8 dB insertion loss. The combined notch attenuation was about 87 dB, but the pass loss was far too high. After studying the duplexer for a while, I wondered why the cable harness seemed to be pretty decrepit for a fairly-new duplexer. On a hunch, I dug out the harness info I got from Sinclair and discovered that the previous owner had put a high-split harness on this duplexer before selling it to the Ham, keeping the original low split harness for himself. Once a new low-split harness was purchased directly from Sinclair (about $125, as I recall) and installed, the duplexer tuned up with the expected pass loss of about 1.6 dB. The notch attenuation was within a dB of the previous value, using the incorrect harness. As I recall, the low-split Sinclair harness had jumpers that were about 2" longer than the high-split jumpers. Even though theory may dictate otherwise, this particular incident with this duplexer proved to me that incorrect jumper lengths between cans may have a profound effect upon pass attenuation, and almost no effect upon notch depth. YMMV. 73, Eric Lemmon WB6FLY -----Original Message----- From: [email protected] [mailto:[EMAIL PROTECTED] On Behalf Of Jeff DePolo Sent: Saturday, January 21, 2006 9:16 AM To: [email protected] Subject: RE: [Repeater-Builder] Re: Duplexer retune / recoax > The length of the jumper cables between the cans has a profound > effect upon the insertion loss at the pass frequency, and relatively > little effect upon the isolation at the notch frequency. > > 73, Eric Lemmon WB6FLY Eric, I'm curious why you say this, as it contradicts what I would believe to be the case in theory... <The remainder of Jeff's scholarly letter is snipped for brevity> 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/
