Elecraft KSB2 User Manual

Page 22

Power Control and ALC

Tracking ALC: SSB transceivers use Automatic Level Control (ALC) to reduce transmit drive if output
exceeds a desired level. Many transceivers require that you adjust the mic gain manually until the ALC
indication is in a certain range. The K2's ALC is different: the drive level is automatically adjusted, over
time, to keep ALC close to the optimal level. This tracking ALC (TALC) eliminates the need to adjust mic
gain in most cases. You can set the POWER control, mic gain, or speech compression to any level, and the
ALC level will average between 1 and 3 bars (in ALC meter mode) as you talk.

POWER control: This control is used to set the desired SSB peak power output. The maximum is about
10 to 15 watts PEP, depending on the band, antenna impedance, and power supply voltage.

The minimum

power output in SSB modes is about 1 watt, even if you set the POWER control below this level. (If you set
the POWER level near maximum, the ALC indication will typically be between 0 and 2 bars. Low power
settings (3 watts or less) will result in about 3 bars on average.) Other POWER considerations:

1. Don't set the POWER control any higher than the transmitter is capable of. For example, if you

hold TUNE and find that you can only get to 9 watts on 10 meters even with the POWER control all
the way up, you should use POWER settings of 9 watts or less on 10 meters, in all modes.

2. Use lower power when using a battery. Don't use > 10 watts unless you're running from 13-15V.
3. Set CAL CUR to no more than 3.5 amps. This will allow the K2 to remind you when the PA

transistors are drawing too much current, so you can reduce power before they get too warm. If you
see a HI CUR warning message, reduce power until the warning goes away.

4. If you get a mic burn or a report that your signal is distorted: This is usually an indication that you

have high RF voltage on the K2 chassis due to the use of an end-fed or poorly-matched antenna. The
problem can be solved by using an RF Isolator, available from Elecraft and other manufactures.

5. Use 5 watts or less for digital data modes, since the duty cycle for digital modes can approach 100%.

Use 1:1 or 2:1 speech compression for minimum data distortion (SSB C 1-1 or 2-1 ).

SSB Transmit BFO Optimization (Important)

When you transmit using SSB mode, the fixed filter on the SSB adapter is always used (OP1). The way
your voice sounds to other stations depends on the BFO settings for this filter (i.e., BF1 in CAL FIL).
Table 3 provides BF1 values for LSB and USB based on the measured crystal filter frequency (from page
10). However, you may have to experiment with these settings, adjusting them slightly to obtain best voice
quality. You can use another ham-band receiver, or ask a nearby station listen to your signal as you vary
BF1. Use CAL FIL, moving the BFO as much as +/- 200 Hz from the frequencies shown in Table 3. Start
with lower sideband, then upper. Moving the BFO too close to the filter will worsen carrier rejection, so be
sure to re-check carrier amplitude whenever you change the BFO setting.

Note: The BFO settings for LSB and USB are swapped on 15, 12 and 10 meters due to the K2's frequency
mixing scheme. If you use 17 m or below for making BFO changes, the following rules apply:
LSB: moving the LSB BFO lower in frequency will raise the voice pitch and improve carrier rejection.
USB: moving the USB BFO higher in frequency will raise the voice pitch and improve carrier rejection.

Operation above 10 watts PEP output may result in a small increase in transmit IMD.