[Elecraft] [KX3] JT65-HF KX3 PA Temp Testing

[Gary Hawkins]

Last night I did some monitoring of the KX3 PA temp.  My setup as 
follows: Barefoot KX3 fitted with VE3FMN heatsink.  PSU 13.8V, 14.076MHz 
operation into dummy load, ambient air temp 21C. Set ALC = 4 occasional 
flicker 5.  WSJT-X S/W and Signalink

The test consisted running 6 CQ cycles of JT65-HF and noting PA temp at 
end of RX and TX segments.  Therefore lowest and hottest points in cycle 
assuming no thermal overshoot.  The TX signal is approx 47 secs long and 
consists essentially of a CW carrier of varying frequency (less than 
200Hz bandwidth).  The RX cycle is one minute and 13 secs long, so one 
complete TX/RX cycle takes exactly 2 mins.

Results as follows:

0.1W TX, min temp 29C, max temp 38C, typical temp variation of PA temp 
in TX cycle 8 - 9C
0.5W TX, min temp 29C, max temp 40C, typical temp variation of PA temp 
in TX cycle 8 - 9C
1W TX, min temp 29C, max temp 40C, typical temp variation of PA temp in 
TX cycle 8 - 9C
2W TX, min temp 30C, max temp 41C, typical temp variation of PA temp in 
TX cycle 8 - 9C
3W TX, min temp 29C, max temp 41C, typical temp variation of PA temp in 
TX cycle 8 - 9C
5W TX, min temp 30C, max temp 48C, typical temp variation of PA temp in 
TX cycle 13 - 15C

I also did a long term JT65_HF CQ sequence over 12 cycles at 3W to see 
the where max PA temp stabilized.  It appeared to be 42C, with typical 
min to max temp PA range of 34 to 42C over TX cycle.

I was surprised not to see more degradation on going from 2 to 3W as 
this takes the PA from high to low efficiency mode.  At 5W the KX3 PA is 
showing a considerable increase in thermal stress, sweet spot of my KX3 
appears to be 3W or below.

I'd be interested to hear any comments/thoughts on these findings.

73's Gary K6YOA