[Elecraft] Shutdown on 50MHz CW

[Paul G4LNA]

My first reaction is it sounds like RF getting in somewhere, as a matter of
interest does it happen when you run it into a dummy load?

73 Paul


GM3SEK wrote:
> 
> Ian J Maude wrote:
>>Having used the radio for a while I am now starting to come up with 
>>some questions.  The first one comes from using RTTY in contests.  I 
>>generally have the display showing me the PA temp and I stated to 
>>wonder, what *is* the optimum temperature for the PA?  Also, I can see 
>>it is rising but I have no idea when it should get critical :)
>>Any clues please?
> 
> No answers, but maybe a related question...
> 
> The rig is a K3 with KPA100 and KAT3.
> 
> Having just started to use the K3 intensively on 6m, there is a problem 
> with the PA shutting down, especially on CW. After 10-20 seconds of 
> operating, the RF power disappears. Many of the symptoms are 
> intermittent, showing no clear pattern - except that it only happens on 
> 50MHz.
> 
> Moments before the power dies, there are one or two warning clicks of a 
> relay. There may also be a "HIGH SWR" warning, but not always - 
> sometimes that warning flashes and it's still possible to carry on for 
> 10-20 seconds. (The SWR is actually OK - tested at 100W using another 
> rig, and on a dummy load.) The problem is the same on both ANT1 and ANT2 
> outputs of the KAT3, and either with or without the auto-ATU.
> 
> The problem cannot be cleared by cycling TX/RX; but it can always be 
> cleared (at least temporarily) by cycling ANT1/ANT2. That brings the 
> power back, making it possible to limp through a short QSO.
> 
> However, there *may* be some relationship to the PA temperature. 50MHz 
> is the only band on which the PA temperature indication is being 
> affected by RF - on CW, it bounces upward by anything up to 5degC on 
> every key closure, and I'm wondering if these  transients are triggering 
> a PA shutdown.
> 
> There is no problem on any other band. On 28MHz, I ran off a string of 
> CW QSOs in the contest, and then tested the KPA100 for about 5 minutes 
> at 120W continuous carrier. There were no RF-related effects, and the PA 
> temperature levelled out at about 60degC. It seemed quite happy at this 
> temperature.
> 
> Back on 50MHz, continuous carrier caused the same kind of instant jump 
> in the indicated PA temperature. The TX did eventually shut down, but 
> the transient changes seem to have more effect than the actual PA 
> temperature. There is no problem with SSB, but the PA temperature 
> genuinely is lower on that mode. CW seems to be the worst mode because 
> the duty cycle is higher and it also creates lots of transients.
> 
> 
> It's all a confusing mess of symptoms... and I may not even be on the 
> right track with the PA temperature. However, I feel pretty sure that 
> the problem *is* being caused by internal stray RF.
> 
> 
> Since it's Memorial Day, it won't be reasonable to expect a response 
> from support at elecraft.com for at least another 30-40 hours. In the 
> meantime, I'd be grateful for any thoughts and suggestions from the 
> group.
> 
> 
> -- 
> 
> 73 from Ian GM3SEK
> http://www.ifwtech.co.uk/g3sek
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