[Elecraft] To PLL mod or not

[Mike Harris]

Hi,


> A drift in local oscillator frequency is the same as changing the main
> tuning dial. It won't change the relationship of the signal to the
> filter bandpass.

Altering the main tuning, either by intent or VCO drift, will move a
signal within the passband of the filter, it has to, how could one move
on to another signal otherwise.

> Changing the BFO should be the only way to change the position of the
> signal in the filter passband, if I understand how the thing works
that
> is...

With respect to zero beat or your desired sidetone.  VCO drift will also
alter the side tone frequency, as in normal tuning, but not the
relationship between the BFO and the filter.

We are dealing with two separate issues here, hence the need for two
cures.

1.  To remove the necessity of retuning to keep the signal within a
narrow filter.
2.  To remove the problem of BFO drift causing a change in side tone
frequency whilst keeping a signal within a narrow filter.

It has to be looked at both ways, whatever effects receive with also
effect transmit, that is the transmit signal will also drift.

This morning at switch on I tuned onto a birdie just above 28MHz (150Hz
filter), probably 7th harmonic of the KPA100 bus clock.  After 45
minutes I had to retune up 210Hz.  Interesting but useless 'cos it
introduced a third variable.

Regards,

Mike VP8NO
#1400