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
