- Wider bandwidth in SSB filter, so I took it from 2.4 to 2.6 kHz (KI6WX)
- More sensitive VOX (G3RXQ)
- RF-filtering on audio input (G3RXQ)
All of these are modifications to the tighly packed KSB2 board shown above so it took some patience to implement them. The bandwidth modification consists in replacing six ceramic capacitors that were sitting between the crystals. The VOX sensitivity modification is done by adding a pot which can be seen in the image as it sits outside the PCB on the left-hand side. I was lucky to find a mini 5k slider pot in my junk box which fitted in. Finally the RF-filtering was done by adding an inductor of 2.5 mH (right below the 5k pot) and a decoupling capacitor.
All of these modifications can be found in the KSB2 section of the guide to modifications.
The barebone K2 has a limitation with continuous transmission and the manual says:
- Since some RTTY/data mode duty cycles approach 100%, you should reduce power to about 5W or avoid transmitting at 10W for longer than 1-2 minutes at a time. (Power levels above 10 W are not recommended.)
- Duty cycle 5 W, 100%; 10 W, 50%
The 100 W option, the KPA100, is more restricted and the manual says:
- The maximum recommended power for PSK31 mode is 40 W, and for higher duty cycle modes such as MFSK, 25 W.
- Key-down time: At full power (100 W), 10 sec max. recommended
The KPA100 can do FT4 at near 100 W it seems since it only transmits for 4.5 seconds, but not FT8.
Finally, changing the SSB bandwidth meant that the BFO frequencies had to be set up again. It was fun to do this again as I haven't done it for many years now. Using the nice Java program from AB3AP, K2Params, for reading the K2 Control parameters, I was also able to read out out the new values for backup. Some of them follow here. The "RTTY rev" mode is the preferred one for FT4 and FT8.
CW: FL1 1.00C FL2 0.70C FL3 0.40C FL4 0.10C
CW rev: FL1 1.00C FL2 0.70C FL3 0.40C FL4 0.10C
LSB: FL1 OP1L FL2 OP1L FL3 1.80L FL4 OFFL
USB: FL1 OP1U FL2 OP1U FL3 1.80U FL4 OFFU
RTTY: FL1 OP1R FL2 2.00R FL3 1.80R FL4 1.60R
RTTY rev: FL1 OP1R FL2 2.00R FL3 1.80R FL4 1.60R
CW: 04913.33C 04913.31C 04913.22C 04913.14C
CW rev: 04914.46C 04914.44C 04914.25C 04914.20C
LSB: 04913.49L 04913.71L 04913.45L 04913.54L
USB: 04916.66U 04916.45U 04915.62U 04916.10U
RTTY: 04913.55R 04913.59R 04913.59R 04913.59R
RTTY rev: 04916.64R 04915.97R 04915.62R 04915.44R