[ARC5] Way OT -- SX-28

[Kenneth G. Gordon]

On 6 Aug 2021 at 17:57, MICHAEL BITTNER wrote:

> As I understand it Oswald G. Villard's "Select-O-Ject" and a
> Q-Multiplier are entirely different animals.  The Select-O-Ject uses a
> series of RC phase shifters to select a frequency for boosting or
> rejection.  There are no inductors in the circuit.  The Q-Multiplier
> is essentially an LC oscillator operating at the IF that can enhance
> or notch out a selected frequency within the IF passband.  Both use
> phase inversion for the reject or notch function.  Of course there is
> much more on how these two critters work but the above is my attempt
> at describing the essential difference between them.  BTW (name
> dropping here) O.G. Villard was my EE Lab instructor at Stanford. 
> Mike, W6MAB

Essentially correct. "Q-multipliers" work at the IF frequency of the receiver to which they are 
attached.

Normally, the input/output (it is both) of the device is connected either to the output of the 1st 
receiver mixer, or to the output of the 1st IF. Usually, they work better when connected to the 
output of the 1st receiver mixer.

And, when properly aligned, set up, and tuned, they CAN give a single-signal result to some 
of those receivers which don't have enough selectivity alone to do that.

I routinely buy Heathkit QF-1s to add to any of the better receivers which have a 455 kHz IF.

I restore receivers such as the National NC-57, NC-125, and others like that, add a 
Q-multiplier and give the combo to newbies.

One must be extra careful to align the Q-multiplier. Getting it right takes patience and real 
care.

The addition of the Q-multiplier very seriously enhances the selectivity characteristic of the 
receivers I have added one to.

Besides Heathkit, Drake, CE (Multiphase), Hallicrafters, B&W, and several other companies 
made them. Although the Drake model is often considered to be the best one, I have had 
very, very good luck with the Heathkit QF-1. But, as I mentioned, properly aligning it, 
especially the null function, can be somewhat tricky.

The Heathkit QF-1 and its later models exist in far greater numbers than those of any other 
maker.

Apparently, O. G. VIllard also designed the Q-multiplier.

https://www.robkalmeijer.nl/techniek/electronica/radiotechniek/hambladen/qst/1957/04/page2
5/index.html

Ken W7EKB