I think oddities in frequency from the encoder are caused by the
encoder. The processor is dependent on their being two outputs from the
encoder that change at different times. The one that leads indicates the
direction of rotation. If, due to dirt or encoder malfunction, the
sequence isn't followed the processor gets mixed up and goes backwards.
I often suspect lint in the decoder but since many are based on moire
patterns between disks with many slots, a little misalignment can cause
that too. If the encoder can be disassembled for cleaning, I'd try that,
then I'd replace it.
I've seen the same problem in an old IC-211 and it was from dirt (open
encoder) and lint and changing sensitivity on one of the optical
channels.
I saw the same problem in a fairly new FT1000MP a couple months ago and
found that it changed when I pushed on the knob. After the owner slid
the rubber ring off the knob then it acted differently. Time for a new
encoder there too, when end thrust on the knob changes its actions.
If a new encoder didn't fix the problem, I'd add a capacitor to each of
the data lines from the encoder. A shunt capacitor to clean up noise. I
used to have to do that to S-100 bus computer boards that weren't well
designed. If TTL levels, up to 1000 pf from signal to ground cleans up a
lot of high speed noise. I called it a "two terminal type D self clocked
storage element." From hand drive on the encoder you don't need 10
nanosecond response time, 300 microsecond response time is fast enough!
But the processor will respond to hundreds of nanosecond long pulses on
those control lines.
73, Jerry, K0CQ
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