[ARC5] Way OT -- SX-28

[MICHAEL BITTNER]

Yes, I was very lucky to have Villard as my EE Lab instructor.  He gave me an A in that course, mostly for building a transistor amplifier for a medical device for counting blood corpuscles.  This is back in the days when the 2N404 was replacing the 12AU7 in computer flip-flops.

In my previous post, I should have written "The Select-O-Ject uses a series of RC phase shifters to select an AUDIO frequency ----".  I left out the word AUDIO.

RC phase shifters have also been used at RF for noise rejection in devices inserted between antenna and receiver.  Some homebrew ones are described by Mike Murphy, WU2D in the Feb 2014 issue of Electric Radio magazine.  However, to obtain the oppositely phased signals needed to drive the RC phase shifters, he uses tapped inductors rather then the tube-type phase inverters used by Villard. Mike, W6MAB



> On August 6, 2021 at 6:54 PM Tom Lee <tomlee at ee.stanford.edu> wrote:



> 
> 
> Very cool to hear that you knew Villard!
> 
> — Cheers,
> Tom
> 
> Sent from my iThing, so please forgive typos and brevity.
> 
> > On Aug 6, 2021, at 2:57 PM, MICHAEL BITTNER <mmab at cox.net> 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
> > 
> > 
> >> On August 6, 2021 at 4:12 PM Richard Knoppow <1oldlens1 at ix.netcom.com> wrote:
> >> 
> >> 
> >>    Q-Multipliers work at audio. While they can be of 
> >> considerable help they do not eliminate beat images (the beat at 
> >> the other side of a CW signal) or specific QRM, i.e. a single 
> >> signal, like another station adjacent to the one you want. They 
> >> really do not improve the selectivity.
> >>    The original Q-Multiplier was designed by a fellow at 
> >> Stanford U. I am unable to remember his name. The circuit and 
> >> theory was published in QST and a commercial version was made by 
> >> National under the name Select-O-Ject. Heathkit also made a 
> >> version. They operated at audio frequencies so could be used on 
> >> any receiver and did help with very low cost receivers with 
> >> minimal selectivity.
> >>    Of course, the principle works at RF too and some receivers 
> >> were built with RF selector or notch filters. These, like a 
> >> crystal filter, do null out a specific signal and will eliminate 
> >> CW images but the fact that a  Q-multiplier could be used without 
> >> any modification to the receiver made them very popular.
> >> 
> >>> On 8/6/2021 12:50 PM, Hubert Miller wrote:
> >>> You folk remember that ARRL article on the Q-multiplier outboard unit for
> >>> the SX-28 ? It was published, I think, in some edition of the Handbook or
> >>> maybe in QST. Would that addition be for more variable SSB selectivity
> >>> or the notch feature, or actually both ?
> >>> -Hue Miller
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