[ARC5] Way OT -- SX-28

[Richard Knoppow]

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