Modify VHF oscillator/multiplier found in a 150.8 to 174 MHz GE MASTR II radio for better performance.
NOTE: These modifications can be avoided by using high-side local oscillator injection. To do this just order your crystal (or specify the ICOM gets made) for high side injection.
The sensitivity of the stock GE MASTR II commercial receiver may be limited by low local oscillator injection when tuned to the amateur 2 meter band. The problem is more apparent as frequency goes down. The following modifications will improve the injection resulting in up to 4 dB extra sensitivity or more. Usually the commercial band receiver provides fairly good sensitivity in the ham band. We like to end up with about -116 dBm or .35 uV for 12 dB SINAD. When it doesn't meet this specification, 9 times out of 10, it's due to low local oscillator injection when using low side injection.
On the later model Osc/Mult boards, (the ones with the trimmer capacitors), there are a few fixed value capacitors that you need to install or increase in value.
C 407 from a 12 to 18 pF
C 412 from a 5 to 8 pF
C 417 from (unknown value/maybe not installed) to a 3 pF
C 421 from (unknown value/maybe not installed) to a 18 pF
Here are images to help identify the locations of these capacitors.
Copyright 2003, Jeff DePolo WN3A
HTML Copyright April 4 2003, Kevin K. Custer W3KKC
All Rights Reserved.