![]() Just mentioning this it shouldn't have an effect on your AFC Lock problem. I get the feeling that Harris outsourced the PA. However there is a separate schematic for that. The full technical manual on Harris' site is incomplete it doesn't have the power amplifier module. Harris Micromax FM Exciter Operation REV1 SECTION 3 Operation Introduction This section of the manual contains information on how to operate the exciter and covers the following topics: Turning on the transmitter (3.2) Adjusting RF power output (3.3). Many will send the audio to both the VCO and the reference oscillator, modulating both, so the output signal has the proper deviation, but since both inputs to the PLL are being driven by the same low-frequency signal, the PLL doesn't see the low-frequency transitions as loss of lock. At normal audio freqs, the AFC circuit's low-pass filters never see a problem.Ī lot of two-way radios use similar PLL circuitry, but they need to get low-frequencies through without losing lock. Eventually it gets to be too great and you lose lock. The composite input is almost (if not truly) DC-coupled, so any DC or real low-freq AC here can cause the VCO to be modulated to an extent that the PLL/AFC thinks it's going off frequency (effectively, it is), and it can only correct so much error.
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