[ARC5] Way OT -- SX-28

[Michael Hanz]

I was wondering the same thing, Tom.  But here is a brief circuit 
description from http://emmittsfixitshop.com/Projects_HRO_SOJ.html :

/"The name Select-O-Ject is derived from "frequency selective amplifier, 
oscillator and rejection filter." The circuitry consists of two constant 
output audio amplifiers. One can be switched for either zero or 180 
degree phase inversion. The other shifts the phase 180 degrees at a 
specific frequency set by the "pitch" control. Combine the outputs of 
these amplifiers and the resulting signal, at a set frequency, is either 
"rejected" if the two outputs are out of phase, or "boosted" if the two 
are in phase. The circuit uses regenerative feedback, controlled by the 
"boost" pot. This control can be advanced to the point of oscillation. A 
terminal on the back, marked "key" allows keying the oscillator, turning 
the unit into a code practice oscillator. However, the key terminals 
must be shorted in order to use the unit as a filter."

/- Mike  KC4TOS/
/
On 8/6/2021 5:48 PM, Tom Lee wrote:
> 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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-- 
Michael Hanz - KC4TOS

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