"Scott Dorsey" wrote in message
...
gareth wrote:
"Peter Able" stuck@home wrote in message
IMHO, Peter's reply is the correct opening statement of a response to
your
rather unstructured question. If you cannot then use this statement to
seed and to refine your own thought process, it might be more helpful if
you elaborated the point that you think he is missing.

Thanks. but the subject matter seems to have WHOOSHED over your head.

Mine too, I don't really understand what you're asking. The crystal
filter
is a bandpass filter. The phasing control affects the symmetry of the
filter somewhat (but not really all that much).

A single crystal-plus-phasing-control is NOT a bandpass filter. It is
a SINGLE crystal that has a series-resonant peak and a parallel-resonant
notch, and it is most certainly not a symmetrical response curve.

The phasing control affects the frequency of the parallel-resonant notch.

The reason for my query is that googling threw up the instructions for
a Hallicrafters (SX42, I think) that suggested that the BFO could be
adjusted
AFTER the setting of the phasing control, when it seemed to me that such
action
would move the position of the notch AWAY from the audio image and thus
lost the single-signal facility.

But thanks for your contribution.

A single crystal-plus-phasing-control is NOT a bandpass filter. It is
a SINGLE crystal that has a series-resonant peak and a parallel-resonant
notch, and it is most certainly not a symmetrical response curve.

The phasing control affects the frequency of the parallel-resonant notch.

The reason for my query is that googling threw up the instructions for
a Hallicrafters (SX42, I think) that suggested that the BFO could be
adjusted
AFTER the setting of the phasing control, when it seemed to me that such
action
would move the position of the notch AWAY from the audio image and thus
lost the single-signal facility.

But thanks for your contribution.



Gareth,

The answer is quite simple; unless you move the VFO there will be no
need to change the BFO setting. Adjusting the phasing control is akin to
an IF shift control on a modern radio with the addition of a notch to
the side of the passband which you can move with the phasing control.
Adjusting it will have no effect on the frequency of the received signal
merely the range of frequencies in the passband or the notch.


The only reason that the BFO might need adjusting is pulling of the VFO
which was quite common on early receivers due to poor supply regulation
and the like.

73
Jeff