Motorola MICOR High Band to 222 MHz Conversion
Modification Courtesy of SEITS
Original Concept and Images by David A. Cooley N5XMT

Step 1: Remove Exciter PCB and change the following components to the new values shown:

C430 = 68 pf 5% Silver-Mica
C447 = 10 pf NP0 Disk
C433 = 150 pf 5% Silver-Mica
C448 = 15 pf NP0 Disk
C434 = 120 pf 5% Silver-Mica
C451 = 4.7 pf NP0 Disk
C437 = 22 pf 5% Silver-Mica
C452 = 7.5 pf NP0 Disk
C439 = 22 pf 5% Silver-Mica
C455 = 3.9 pf NP0 Disk
C440 = 47 pf 5% Silver-Mica
C456 = 4.7 pf NP0 Disk
C443 = 15 pf 5% Silver-Mica
C458 = 1.5 pf NP0 Disk
C444 = 12 pf 5% Silver-Mica
C460 = 75 pf 5% Silver-Mica
R429 = 49 - 180 ohm 1/2 watt *see below for more information*

MICOR® Exciter Board Layout

Step 2: Reinstall Exciter PCB and tune in accordance with Motorola manual.
Exciter should produce approximately 100 mW.  If something other than 100 mW is needed for driving an outboard amplifier, simply change the value of R429 to obtain the desired drive level.  Don't go below the original value for R429.  Usually something around 49 to 75 ohms is needed to produce 200 mW which is needed to drive the Toshiba SAV-15 properly.

The crystal formula is the same as the original highband formula.  The crystal is just higher in fundamental and is not multiplied differently from the highband method.  The formula of F/12 is still used, where F is the operating frequency in megahertz.  The range of the crystal for an operating frequency of between 222 and 225 will be between 18.5 and 18.75 MHz respectively.

Example:  224.500 divided by 12 is 18.708333 MHz.

Page recreated by: Kevin K. Custer W3KKC
Copyright 1998 SEITS, N5XMT and W3KKC.

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