[ARC5] Way OT -- SX-28

[Tom Lee]

I’ve never seen a Q-multiplier hooked up to an audio chain. I can’t think of why it would help there (what would be the Q of an audio amplifier, and why multiply it??) All the ones I’ve seen work at IF, as that Heathkit does.

Cheers
Tom

Sent from my iThing, so please forgive typos and brevity.

> On Aug 6, 2021, at 1:45 PM, radio_man at wbsnet.org wrote:
> 
> I have a National SAF-1-2 Select-O-Ject, it was hooked to an SX-28 which I
> sold a while back. Yes it connected to the audio chain. The National also
> has a terminal to connect a key so you can use it as a code practice
> oscillator I also have a Heathkit QF-1 Q-multiplier, it does not hook to
> the audio circuit, rather connects to the 455Kcs (Khz) IF at the mixer.
> 
> Rod
> K0EQH
> 
> 
>>    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
>> 
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