[Elecraft] An idea for the K2

[Stewart Baker]

 On Wed, 2 Mar 2005 08:00:59 -0800 (PST), John Magliacane wrote:
>
>
> --- WA2JJH at aol.com wrote:
>
>> I use my K2 on CW and SSB. I was wondering how K2 Hams would feel about
>> different
>> grades of SSB adapters.
>>
> I would sharpen up the skirts on the audio chain (300 - 2700 Hz) with
> active filters prior to the compressor.  (There is no reason for any energy
> outside this spectrum to be passed along (and influence the operation of)
> the compressor and the balanced modulator, since the crystal filter is too
> narrow to pass it, anyway.)
>>
>> Reducing the values of the coupling capacitors in the audio chain makes a big 
>> difference (what purpose an audio response that goes down to 30Hz ?!)  
>
> Add some gain (accomplished through the active filtering stated above), and
> provide a mic gain control (on the board).
>
>> Get rid of the mic attenuator circuitry (does anyone use it ?) and add an 
>> adjustable mic gain of 10dB (well rf filtered) to the board.

>> Replace the existing compressor IC with a later version that has an
>> adjustable threshold level.

>> Totally revamp the VOX circuitry and add Anti-VOX. Make both hardware
>> adjustable.

> It might be nice to replace the NE602/NE612 with a switching-style
> balanced modulator for the following reasons:
>
> * The BFO (VXO) injection voltage into the NE612 varies with the BFO
> setting and USB/LSB switching.  The NE612, being a linear mixer, is
> sensitive to this.  It's DSB output voltage varies according to the BFO
> injection voltage, as does it's carrier suppression.
>
> * A well-designed switching mixer is inherently self-balanced (assuming
> matched resistors, minimal stray capacitance, and low offset voltage
> OP-AMPs are used), eliminating the need for the carrier balance control
> and one less adjustment for builders.
>
> * More dynamic range (limited only by the output swing of the audio feeding
> the modulator and the supply voltage to the analog switches), leading to
> even less SSB TX distortion (IMD) and carrier suppression than is
> possible now.
>
>> I would like to know more about using a switching mixer for the BM.
>> If the circuitry does not get too complex or introduce problems it would be 
>> worth trying. Please let me have more information.

>> 73
>> Stewart G3RXQ

> Good luck with the project!
>
>
> 73, de John, KD2BD
>
>
> =====
> Visit John on the Web at:
>
> http://www.qsl.net/kd2bd/
>
>
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