Maximizing battery life of Elecraft KX3 QRP

Battery life can be improved by minimizing the KX3’s receive and
transmit current drain.


The KX3 already has far lower receive-mode current drain than most all-
band/all-mode transceivers, but you can further reduce it in several

– use headphones (10-100 mA saved depending on volume level)
– turn off the LCD backlight (25 mA)
– turn off the RX I/Q port when not needed (10 mA; see MENU:RX I/Q)
– turn off the preamp (5 mA saved for the 20 dB preamp,
10-15 mA for the 10-dB preamp)
– turn off the RX isolation amp (10-15 mA; see MENU:RX ISO)

Using all of the above techniques, receive-mode current drain can be
as low as 150 mA, varying a bit per-band.


In transmit mode, current drain varies with power level, supply
voltage, band, and load impedance. An antenna tuner (such as the
internal KXAT3 option) can help ensure the transmitter sees a good

There are some thresholds where the transmit current drain is
automatically reduced by switching in a higher-impedance PA output
transformer winding. In this case a decimal point is added to the
right of the power display when you adjust it (e.g., “3.0 W.”). Here
are the conditions under which TX current is reduced:

1.  5.0 W or less in CW, FSK-D, and FM modes when key-down supply
voltage is 11 V or higher

TX current in this case is typically 1 amp — about 50% lower than
what you’ll see if you move power just a bit above 5.0 W. This is
especially useful for QRP Field Day outings (etc.) where the rig is
powered from an external 12 to 14 V battery.

2.  3.0 W or less in all modes, regardless of supply voltage

This is the generally recommended power level when operating from an
internal NiMH battery pack. If you’re more interested in power output
than operating time, you can run up to 5 watts from the internal