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

[Gary Hawkins]

I did a little additional PA temp testing today, this time focused on 
simulated JT65-HF 10m operation.  Setup the same as below except 
transmitting on 28.076MHz operation into dummy load.  Results as follows:

2W TX, min temp 29C, max temp 43C, typical temp variation of PA temp in 
TX cycle 11 - 12C
3W TX, min temp 29C, max temp 43C, typical temp variation of PA temp in 
TX cycle 14 - 15C
5W TX, min temp 30C, max temp 54C, typical temp variation of PA temp in 
TX cycle 19 - 20C

The KX3 is clearly under more thermal stress operating on 10m rather 
than 20m, and the sweet spot appears to be in the 2 - 3W range.  5W 
operation showing a marked increase in cycle-to-cycle temp variation.

Does anyone know how I can estimate KX3 freq drift before and after temp 
compensation as I don't have an easy way of measuring it? Again, I'd be 
interested to hear any comments/thoughts on these findings.

73's Gary K6YOA


On 5/13/2015 9:09 AM, Gary Hawkins wrote:
> 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