In message , Michael Black
writes
"M. J. Powell" ) writes:
In message ,
Frank Dresser writes

"bobinphx" wrote in message
news:L6KCc.1254$Ph.98@fed1read06...
To All,
I just purchased a Lafayette kt-200 and research on the net says it has a
jack for a Q multiplier. Further research on a Q multiplier shows that is
some how acts like crystal filter, only variable and it appears that it
can
also boost poor signals??? Can someone give me a readers digest, not
overly
technical explanation of "how do it work" ?????

I scanned this, not from the Reader's Digest, but from the 1964 ARRL
handbook:


The "Q Multiplier" is a stable regenerative stage that is connected in
parallel with one of the i.f. stages of a receiver. In one condition it
narrows the bandwidth and in the other condition it produces a sharp "null"
or rejection notch. A "tuning" adjustment controls the frequency of the peak
or null, moving it across the normal pass band of the receiver i.f.
amplifier.

The shape of the peak or null is always that of as single tuned circuit
(Fig. 2-50) but the effective Q is adjustable over a wide range. A Q
Multiplier is most effective at an i.f. of 500 kc. or less; at higher
frequencies the rejection notch becomes wide enough (measured in cycles per
second) to reject a major portion of a phone signal. Within its useful
range, however, the Q Multiplier will reject an interfering carrier without
degrading the quality of the desired signal.

In the "peak" condition the Q Multiplier can be made to oscillate by
advancing the "peak" (regeneration) control far enough, and in this
condition it can be made to serve as a beat frequency oscillator. However,
it cannot be made to serve as a selective element and as a b.f.o. at the
same time.


and how well does it
work????

They work well, within their limitations. The peak bandwidth can be very
sharp, but off the peak the curve slopes down more gently and doesn't
provide a dramatic difference in adjacent channel rejection. The sharp
bandwidth of the peak makes the adjustment very sensitive to drift.

Q multipliers don't produce a null and peak as a single crystal filter does.



In addition any suggestions as to which model, of the many that heathkit
sold, would be, arguably, the best for this application.....

If you can get some B+ and heater power from the receiver, the Heathkit
QF-1 works well. There are other models with internal power supplies.

These things are sensitive to power supply hum. It may help to decouple the
Q multiplier power through a series resistor and another electrolytic cap.

The OP may care to look up the 'Select-o-Ject' which was a modified
'Q-Multiplier' which could produce a notch.

Mike

I thought the "Select-o-ject" was an audio filter. From Villard, if I'm
remembering properly.

I can't say I've ever seen any attribution for the origins of the
Q-multiplier. Obviously, it's a step away from the regenerative receiver,
but I've never seen anything about who first connected it to the plate of
the mixer in a receiver for this purpose.

You may well be right! Please erase my comments from your respective
memories.

Mike