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
Re: [Repeater-Builder] Question re: Crystal Ordering for UHF MICOR Receiver
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
[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
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
RE: [Repeater-Builder] Question re: Crystal Ordering for UHF MICOR Receiver
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
