[Elecraft] KSB2 Increased Gain Modification

[Ken Wagner]

Hi Mike:
Yup... that's what I was referring to. I picked this up in the digest mode 
after a week in KP2 and guess I didn't have the complete thread.
As you note, the reduction of IMD that John G. addresses is really only 
needed  when the increased mic gain mod has been made. None of the KSB2s 
that I have built have needed the increased gain to obtain satisfactory 
output.
BTW, I just built 2 KSB2s and configured them at the 2.5 kHz bandwidth. I 
really like it that way.
73,
Ken K3IU
~~~~~~~~~~~~~~~~~~~~~~~~
At 06:50 PM 11/10/03, you wrote:
>G'day,
>
> > I'm pretty sure that you will find that the "IMD mod" *has* been
> > incorporated into the KSB2... a long time ago.
>
>I think you might be referring to the ALC time constant change to improve
>IMD in PSK31 transmissions, this is just a few component changes.  These
>component changes are now standard KSB2 issue.
>
>The other mods from KI6WX are:
>
>1.  Crystal filter bandwidth for which most reports seem to favour 2.5kHz.
>2.  Increased gain of the order of 10dB by circuit changes around U5
>(balanced modulator).  Improves output on 10 metres due to marginal gain in
>the KSB2.
>3.  Reduced IMD by adding a resistor across U5 pins 1 and 2 to reduce
>clipping on its input. Note: this should only be done in conjunction with
>(2.) above otherwise the resulting drop in gain of the order of 6dB will
>make the overall KSB2 gain even more marginal.
>
>It seems that most of the problems with low audio from mic's should be
>overcome by (2.) above, merely adding af gain will drive you into the IMD
>situation (3.)
>
>I see a little mod kit coming on.
>
>Regards,
>
>Mike VP8NO (IOTA SA-002)
>GQRP 10148
>QRP-Canada #57
>K2/100 #1400