[ARC5] Way OT -- SX-28

[Richard Knoppow]

    Thanks for giving me his name. Villard wrote a lot of 
interesting articles and you are lucky to have had him as an 
instructor.
    I probably am confusing two different circuits. A sharp 
filter working at the IF frequency would be considerably more 
useful than one working at audio but I am sure there was an audio 
version.

On 8/6/2021 2:57 PM, 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
>
>
>> 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

-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL