Out of interest I've just completed a test run on K2 #1400 with the
K2 > Oak Hills Research 100W load > sampled by a -20dB coupler > Oak
Hills research WM2 QRP wattmeter terminated with a precision load good
Room temp 20C
K2 set to 20W out, 28.5MHz, confirmed by wattmeter.
The mosquito came on after three minutes of 20W tune power. 8A from PSU.
After about 15 minutes of tune the KPA100 heat sink reached 58C measured
by a laboratory thermometer. Hand said the same thing, could only touch
it for about three seconds.
Set CAL tPA to track cool down and compared with the thermometer. Good
The mosquito shut off at 37C indicated by K2 tPA reading.
Seems normal that the mosquito will come on during an extended run of
psk at 20W output. The exact timing will depend upon how well the CAL
tPA has been set, duty cycle and ambient temp.
If you don't like the mosquito then blow the KPA100 heat sink with a
small 12V PC fan. This is what I did during weeks of overnight QRSS
beaconing on 40M for the RSGB propagation committee grey line study.