[Elecraft] KX2 improvement: up to 2x more operating time at 10 W from internal battery

[Wayne Burdick]

Those who operate the KX2 at a full 10 W from its internal battery pack may have noticed that power automatically drops to 5 W after a certain amount of time.

A few months ago, Rich (AC7MA) pointed out that this was occurring when the battery still had 60-65% of charge remaining. So we definitely weren't getting as much 10 W operating time as we could. That extra 3 dB (1/2 S-unit) can be the difference between being heard -- or not. 

We have a new field-test firmware release that provides approximately twice as much operating time at 10 W. This was accomplished by changing the supply voltage required for 10 watts from 10.0 V down to 9.0 V. 

Note that this change only applies to CW mode. Voice and data modes still require 10 V minimum in order to ensure acceptable transmit IMD levels given the FET PA devices. But since a large percentage of SOTA and general field QRP activity is in CW mode, many users should benefit.

In lab tests, a KX2 with the new firmware transmitted a continuous CW message (no gaps) at 10 watts for 90 minutes before dropping to 5 W. It then ran for another 20 minutes at 5 W before shutting down. Calculations show this amounts to about 78% utilization of the internal battery at 10 W, then another 15% utilization at 5 W. This is a much better tradeoff. 

Actual transceive time at 10 W TX will of course vary with duty cycle. Typical CW SOTA operation has a very high duty cycle, as much as 50% transmit time. That 90 minutes would then translate to some 180 minutes (3 hours) of rapid-fire SOTA CW time at 10 W on a single battery charge. Other QRP activity, such as hunt-and-pounce contesting or rag-chewing, often has a much lower duty cycle -- averaging perhaps 10-20% transmit time. That would mean some 6 to 12 hours of operation at 10 W.

If you're a CW op and you'd like to give the new firmware a try, please contact me directly. I'll send it to the first 20 or so requesters to make sure we give it a good shake-down before releasing it as beta.

Additional KX-line firmware updates are in progress and will be made available as time permits.

73,
Wayne
N6KR