We have chased an intermittent anomaly in the SR-400 and SR-2000 for some time and finally got a snapshot. When aligning the radio we would occasionally see a significant high level overtone at about 280MHz throughout the radio. Originally thought it was from outside. Put a spectrum analyzer to work and found it to be 280MHz pulses at 1KHz intervals. We had seen this in several radio's and traced it to component placement.
Look in the schematic for C198 and C208. You will find them back to back on a terminal strip --- simply separate them 1/4 inch and the problem will not occur. They cause a feed back loop in V19 the mike amp. Below are snapshot's from the scope and spectrum analyzer.
Kindest regards Jim K9AXN
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This page last updated 25 Jan 2017