[Elecraft] To PLL mod or not

[Mike Harris]

Hi,

> "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."
> ----------
> I believe what Mike meant to say is, "VCO drift will also alter the
pitch
> of the received signal."  Sidetone frequency can only be changed by
the
> ST P menu.

I agree, my reference to side tone was the "pitch" of the received
signal which I accept is not the same thing.  Apologies for the
confusion.

> "We are dealing with two separate issues here, hence the need for two
> cures.
>
> 1.  To remove the necessity of retuning [the VFO knob] to keep the
signal
> within a narrow filter."
> ----------
> True if only VFO drift is the problem.  Not true if BFO drift is the
> problem.
> ==========

Which leads on to point (2).

> "2.  To remove the problem of BFO drift causing a change in side tone
[pitch]
> frequency whilst keeping a signal within a narrow filter."
> ----------
> BFO drift does not cause a change in sidetone frequency.  It causes
the
> filter passband to drift away from the sidetone frequency.  The result
of

It causes a divergence from the circumstance where the "pitch" and the
"side tone" are the same and at the same time coincidental with the
received signal being within the pass band.

> this is that, when the signal is tuned in for max strength (max
reading
> on the S-meter), it is not within the filter passband and therefore
> cannot be heard or is heard very weakly, just like any other signal
> outside of the passband.

I'm not sure you mean to say that.  If the signal is tuned for max
reading on the S-meter surely it's within the pass band.

But if you retune to put the signal back in the pass band of the filter,
the pitch of the signal will have changed and as Ron AC7AC pointed out
it will no longer be zero beat with the internally generated "side tone"
which I assume it's not derived from the BFO (check circuit).  Now,
without the benefit of having the circuit in front of me I have a
feeling that keeping the signal within the pass band of the filter,
despite the changing received "pitch" the transmit signal will remain
more or less on "net", so to speak, as much as it ever was in the first
place.  If this is the case using "split" will enable compensation for
drift on receive but at the same time let the transmit diverge from
"net" causing the other station to have to retune.

I'm beginning to think we are going around in circles here.  The whole
object of the mod's are to reduce two known sources of drift and
indications so far are that they do significantly.

As a mater of interest who uses the "spot" function, me, almost never.
However, I did this morning on the 28MHz birdie and much improved it was
too after adding the 47k ohm resistor mod on the control board, but
that's another story.

Regards,

Mike VP8NO
#1400



> ==========
>
> "It has to be looked at both ways, whatever effects receive will also
> effect transmit, that is the transmit signal will also drift."
> ----------
> True for VFO drift, but not true for BFO drift.
>
> 73, de Earl, K6SE