OK thanks - I'm trusting then also that I can do the same on UHF, order high-side injection crystals for my KXN1024A UHF Receiver channel element and leave the discriminator diodes as they are.
Thanks again, Larry -----Original Message----- >From: Eric Lemmon <[EMAIL PROTECTED]> >Sent: Jan 1, 2007 8:30 PM >To: Repeater-Builder@yahoogroups.com >Subject: RE: [Repeater-Builder] Question re: Crystal Ordering for UHF MICOR >Receiver > >Larry, > >I don't think the diode polarity matters, unless you are using channel >elements with built-in AFC controls. I've converted a few high-band VHF >MICORs without touching the diodes, and they work just fine. > >73, Eric Lemmon WB6FLY > > >-----Original Message----- >From: Repeater-Builder@yahoogroups.com >[mailto:[EMAIL PROTECTED] On Behalf Of >[EMAIL PROTECTED] >Sent: Monday, January 01, 2007 4:22 PM >To: Repeater-Builder@yahoogroups.com >Subject: [Repeater-Builder] Question re: Crystal Ordering for UHF MICOR >Receiver > >I've been following the recent thread about using high-side injection >crystals in the GE Receivers. I've tried that on both VHF and UHF MASTR II, >MVP, EXEC II, etc., and that always worked out well. > >I have several 2-Meter and UHF Motorola MICOR Repeaters locally, and they've >been in operation for so many years that I never gave a thought about >ordering high-side injection crystals for any of the receivers. They always >seemed to work very well just sending them in to ICM and having them rebuilt >for the new frequencies using the standard crystal formulas. Some of the >Repeaters I inherited with the channel elements already re-crystalled, and >none of the receivers' elements had been ordered with high-side injection. > >I'm just getting ready to send in another pair of UHF MICOR elements to ICM, >and am wondering if I will gain anything by requesting that the Receiver >element be recrystalled with a high-side injection crystal? Someone recently >mentioned that I'd need to reverse the diodes in the discriminator if I do >that, so that the AFC will work properly. > >In a VHF MICOR Receiver, there are just two diodes that need to be reversed, >when moving a high-split Receiver down to the 136-150 MHz range. Looking at >the UHF MICOR Receiver schematic, I see that there are four diodes. Which >ones get reversed, if you're changing the injection to high-side? The two >"output" diodes, or all four? The Motorola service manual part numbers for >the diodes (in both the VHF and UHF Receivers) are listed as P/N # >48D84616A01 - "Diode, Planar hot carrier". > >I know these diodes are rather small and quite fragile. They're difficult to >unsolder and then resolder after reversing polarity without breaking them, >as careful as I've tried to be. I did that on several of the 2-Meter MICOR >Receivers that I completely rebuilt with 136-150 MHz factory parts. >Sometimes the diodes broke, sometimes not. Someone on the list recently >mentioned this diode fragility problem, and recommended that the user plan >for replacement as part of the Receiver frequency change project, rather >than trying to reuse the original diodes. > >If there's any advantage at all to going with high-side injection on this >latest UHF MICOR Receiver, I'll go ahead and order some new diodes from >Motorola, just to be ready for any that I break. But how many, and which >ones get reversed? > >LJ > >
