"Lynn" wrote in message
...
circuit theory. The trick is finding one which is not
overly mathematical.
Richard Knoppow
Yes, I must agree with Richard's well written
explanation of
the effects of overcoupling (more than critical coupling).
However
I do not believe that in the instance of the 453's 85kc IF
cans that
with the rods pushed all the way in that they became
overcoupled.
With resultant double peaked bandpass.
This is of course is just my observation with a bit of
practical measurment
using relatively crude methods. It would seem then,to me,
that the double peaked
curve encountered with overcoupling (more than critical
coupling)
is, in this instance, not the condition that results in a
narrower bandpass
when the coils are moved further apart.
During the glory days of TV service, IF alignment
with sweep generators and
oscilloscopes, it was quite fascinating to see theoretical
bandpass tuning in the
real world. Overcoupling was often (always?) used to
achieve the necessary wide
bandwith for a TV channel. While transformer coupling was
not normally
adjustable, the peaks and skirts of the quite wide
bandpass could be moved
around with the adjustments available, and measured with
fairly simple equipment.
But I digress (a lot, sorry)
Old Chief Lynn
A lot TV sets and other equipment with wide band IF's
used stagger tuning. This works fine but is a PITA to align.
As you say a sweep generator, markers, and a scope are the
only way. Actually, I've found sweeep alignment of standard
plain vanilla IF's is often helpful especially if you want
to get the peak symmetrical.
I've tried to find a schematic or other info on the
BC-453 but have not so far been able to. Evidently the IF is
different from other command sets. There is plenty of info
on the other receivers and transmitters but somehow this one
seems to have fallen through the cracks.


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Richard Knoppow
Los Angeles, CA, USA