Power output on the KX2, KX3, K3 and K3S can be set as low as 0.1 W directly using the PWR control.
However, you can actually set power output to much lower levels (< 1 milliwatt), with fine control, by turning off ALC in the menu and adjusting the drive level manually.
Here’s the recommended procedure for accurately setting power to levels below 0.1 watt:
1. Connect an external milliwatt meter between the transceiver and the antenna or dummy load. If you don’t have such a meter, you can alternatively connect a dummy load (such as the Elecraft DL2) then use an oscilloscope or an RF voltmeter. (The DL2 includes a rectifier so you can just use a DC voltmeter. The manual for the DL2 provides a translation from DC volts to power level.)
2. For most accurate results, bypass the ATU. This is done in the menu on the KX2 and KX3. The K3/K3S has an ATU switch function on the front panel for this purpose.
3. Start with PWR set to 0.1 W and verify that you hit about this level on the external meter. Hold TUNE to generate a continuous carrier. (This automatically switches to CW mode temporarily, even if you’re using a different mode.) Then exit TUNE by tapping XMIT.
Note: The 0.1-W level is not well-calibrated at the rig’s internal wattmeter, because this only forward-biases the rig’s SWR detector diodes by a small amount. Also, the SWR (shown on VFO A) will appear as “--“, because reflected power will be too low to accurately calculate it.
5. Go into the menu and turn off TX ALC. This is done using the TX GAIN menu entry on the KX2 (page 41 of the manual) or KX3 (page 49). Use the CONFIG:TX ALC menu entry on the K3 or K3S (approx. page 66).
Note: On all of the rigs, the TECH MD menu entry must be set to ON in order to see the TX GAIN or TX ALC menu entries. This is a precaution to make sure such menu settings are not changed unintentionally. On the KX2 and KX3, you also need to UNLOCK the ALC on/off feature as explained in the manual (MENU section).
6. With ALC turned OFF, the PWR control now directly controls the transmit drive level in fine increments. I just tested my lab KX2 and found I could set the power smoothly down to as low as about 1/2 milliwatt.
When you have ALC turned off, the PWR display (on VFO B) will include an asterisk (*) as a reminder. It will not show actual power level for reasons described above. An external metering method will be needed to dial in the desired level.
Wayne
N6KR
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