[Elecraft] Shutdown on 50MHz CW

[Ian White GM3SEK]

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