[Elecraft] An idea for the K2

[John Magliacane]

--- 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.)

Add some gain (accomplished through the active filtering stated above), and
provide a mic gain control (on the board).

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.

Good luck with the project!


73, de John, KD2BD


=====
Visit John on the Web at:

	http://www.qsl.net/kd2bd/


	
		
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