[Elecraft] SSB related problems

Wed Mar 20 22:02:01 2002

Kevin;

#1:  What is the difference in S meter reading?  This could be dependent on
where the carrier is relative to the filter setting.  When you switch
sidebands, the only things that change are the VFO and BFO frequencies.  The
S meter reading is taken before the BFO mixer, so the only difference it
will see is the carrier being moved from one side of the filter to the
other.  If the S meter difference is small, I wouldn't worry about the
change.

#2  The AC input impedance to U5 is 4 K in parallel with 3 pF when the part
is powered up.  When it is off, the bias network is not activated and the
resistance you see will depend on your meter and how it biases the diodes
inside U5.

The carrier leakage is a function of band, and is most prominent on 40
meters at a power level around 1 mW.  You should easily be able to hear it
in a receiver when the K2 is in SSB transmit (use an external key to put it
in transmit mode) but no microphone is connected to the audio input.  You
can then minimize the S meter reading on the other receiver by adjusting R1.

-John
 KI6WX

>
> 1. USB seems more sensitive than LSB
>
> When I was using an AM station (CHU Canada) to align the filters I noticed
> that I get a higher S meter reading on USB than on LSB. This was with the
> same filter, same frequency, just a simple switch of the mode.
>
> The BFO filter settings were adjusted using Spectogram using the 1kHz
> pulses from CHU. Is this a problem with the alignment of L34 on the RF
> board or is it something else? My K2 does have the SSB filter flattening
> mod installed (in case that comes in to play).
>
>
> 2. Adjustment of the SSB carrier balance
>
> I can use an external receiver to find the minimum signal in LSB mode. In
> USB mode, I can't see any signal at all at 5 watts in to the dummy load.
> Should I just bump the power level and see if I can see a carrier then on
> the external receiver? On LSB minimum signal occurs from approximately the
> 11oclock to 1oclock position of R1.
>
> What is the typical in circuit resistance between pins 1 and 2 of U5 on
the
> KSB2? I expected around 1M due to the presence of R1 but only measure
about
> 10k.
>
> Cheers!
>
> Kevin.  (http://www.interlog.com/~kcozens/)
>