Just what I needed - thanks Kevin! Larry
-----Original Message----- >From: Kevin Custer <[EMAIL PROTECTED]> >Sent: Jan 2, 2007 5:29 AM >To: Repeater-Builder@yahoogroups.com >Subject: Re: [Repeater-Builder] Question re: Crystal Ordering for UHF MICOR >Receiver > >All, > >On a UHF Micor, AFC is not an option, it's a standard feature. UNLESS >you are going to disable the AFC functionality of your UHF Micor >receiver, you'll need to flip the diode polarity - all four, when going >to the opposite injection. There are four diodes in the UHF Micor >receiver as the discriminator rectifiers operate as (I believe) a >voltage doubler; increasing the output voltage available from the >discriminator. I believe this was done for one simple reason; to >eliminate the need of a voltage amplifier to run the AFC varactor in the >channel element. In UHF, because of higher multiplication factor, the >channel element fundamental needs less change to keep the receiver >centered; as compared to a VHF LO. So, in UHF, a Micor discriminator >built with a voltage doubler supplies enough voltage to the channel >element varactor without the need for a AFC amplifier. > >Eric is correct where the VHF Micor receiver conversion is concerned, >unless you are using the K1006 and companion AFC amplifier option, >swapping the diode polarity is not a necessity; UNLESS you are using the >receiver for something like digital communications or in a simulcast >repeater system where audio polarity to the voter is (can be) important. > >A way to remove and swap the polarity of these fragile diodes is to snip >them out with a sharp pair of dikes, instead of de-soldering them. >Then, simply tack solder them back in, after reversing polarity; of course. > >On your 2 meter Micor receivers with Low Side Injection, likely the >capacitors in the LO weren't changed from their original 150.8 to 162 >MHz. values. When converting a 150.8 to 162 split Micor VHF receiver to >the 142 - 150.8 split, you have a choice; change the caps and use HSI, >or leave the caps alone and use LSI. We at Repeater Builder change the >caps and order HSI crystals. > >On a UHF Micor receiver that was built for the 450 - 470 split, ham band >sensitivity can be somewhat less than expected - wanted. Here is an >article that can help with that: ><http://www.repeater-builder.com/rbtip/uhfsensitronRX.html> > >Hope this helps... >Kevin Custer > > >[EMAIL PROTECTED] wrote: >> 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 >> >> >> >> >> >>> 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
