Joe
You just happen to have one of the series of duplexers that does not make it all the way down into the bottom of the ham band at 440.xxx Mhz. If it truly is the Motorola duplexer out of the MSR2000 series repeaters, they - in fact - do not tune down to the bottom of the band. The original T-1500 series duplexers make it fine, but the mechanics of the tuning in these specific cavities "bottom out" before making it to the lowest part of the 440 - 450 MHz. band. What you are experiencing is normal. Trying tuning it up in the 444.9 / 449.9 range, and you will see it works fine. Maybe you can trade it with one that you know will be going on a higher frequency. Interesting timing on your post. I just became aware of this myself a couple of months ago. Bill - W6CBS _____ From: [email protected] [mailto:[EMAIL PROTECTED] On Behalf Of Joe Burkleo Sent: Tuesday, December 02, 2008 11:24 PM To: [email protected] Subject: [Repeater-Builder] Motorola Duplexer Info Needed Hello, I have a Motorola 4 can duplexer out of a UHF MSR2000 series radio that is the pass/notch style. I am pretty sure Motorola also used this same duplexer on the MSF5000 series of radios. I can not find any info on this unit and I am having a problem with the notch on the low pass side. I can not seem to adjust the notch past 4.5 MHz spacing. It will adjust down to 3 MHz spacing just fine. The notch on the high pass side adjusts just fine and will actually go a little beyond the 5 MHz spacing. The pass adjusts properly on both sections of the duplexer. It was originally on 464/469 and I retuned it to 440.8/445.8. The notch problem was there on the original frequency as well. I am using a IFR A-7550 analyzer/tracking generator for alignment. the duplexer has very good insertion loss and the notches are -100 db, so it is meeting specs very well, other than the one notch being off. Has anyone ran across this before or have any ideas. I though I would ask the group, before I started drilling out pop rivets to disassemble the cans from the mounting bracket. Thanks, Joe
