Service Note 2990 AFS issued 21. 2. 2011
Users reported that units from first production lot show more or less a “frequency jitter” effect during strong SSB modulation. The problem occurs as frequency shift of about 100-200 Hz especially if users produce whistle tones into the microphone during the first 10..20 milliseconds of the tone duration. Distant stations report that the tone is not constant and becomes ok later.Reducing the MIC Gain setting can eliminate the problem. The effect becomes as well better after some time of operation of the radio.
Cause: A negative feedback from rising output power with SSB modulation can cause a short time frequency shift reaction of the VCO. The PLL and phase comparator circuits then try to compensate the VCO Varicap voltage.