[Elecraft] KX3 WSPR Thermo Stressing?

[George Pasek]

Thanks for your reply Don.

I read the High Temp Limit is set for 60c so I figure I was not dangerously 
high but just wanted to check if there might be a mechanical preference 
between the shorter duty cycle with the lower temp but larger temp swing 
causing more of a expansion contraction issue over time or the higher duty 
cycle with higher temp but not near as much heating cooling.  I know that on 
some devices the thermo stressing of components due to repeated heating 
cooling cycles is a issue.

This will probably be in continuous use for a while so my concern is the 
long term effects.

I will keep a watch on the temp and maybe add the heatsink as you suggested.

tnx
George
WD0AKZ

-----Original Message----- 
From: Don Wilhelm
Sent: Sunday, September 09, 2018 11:30 AM
To: George Pasek ; elecraft at mailman.qth.net
Subject: Re: [Elecraft] KX3 WSPR Thermo Stressing?

George,

Actually 53 degC is not that hot.  Look at the specs for semiconductors
and you will find that is only a medium temperature.

Actually at 500mW, it is unlikely that the KX3 will be damaged by even a
continuous key-down.

If you are operating it outdoors, you should keep it out of direct sun.

If it concerns you, I would suggest adding one of the aftermarket heatsinks.

73,
Don W3FPR

On 9/9/2018 12:11 PM, George Pasek wrote:
> I am using my KX3 as a WSPR beacon at 500mw with a Arduino based 
> controller which provides GPS time sync, WSPR data, and audio.  Currently 
> I am running mono band at 1 two minute transmit cycle per 10 minute time 
> block.  Now I want to add KX3 band switching to my controller and increase 
> my T/R duty cycle.  Watching the PA.I current I see that my current 2 
> minute ON 8 minute OFF cycle shows a 30c ON – 46c OFF temp range.  Running 
> a 2 minute ON 2 minute OFF cycle shows a stabilized 36c – 49c range after 
> about 5 ON/OFF cycles, and running continuous transmit cycles stabilizes 
> at 48c – 53c after 6 cycles.  So based on these 3 duty cycles I see a 16c, 
> 13c, and a 5c temperature rise.  The 2 on/8 off has the lowest max temp 
> but the widest temp range, the continuous transmit has the highest max 
> temp but the lowest range.  My plan would be to have my controller switch 
> the KX3 through 5 bands transmitting the 1 minute 53 seconds on a band and 
> switching to the next band during the 7 second opening.
>
> I have done extended temperature calibration with the XG50 so frequency 
> stability should not be a issue.
>
> My question is, 53c (127f) is hot, are there any thermo stress issues to 
> the PA or the KX3 in general with running any of these three duty cycles? 
> Obviously I don’t want to damage my KX3. 


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