[Elecraft] Bad start to FD - smoked a K3!!!!

[Tom W8JI]

> We had one guy get on 75 with a KW with another on 40.  Guy on 40 didn't
> know.  He got the RFI warning, the K3 locked up and he smelled smoke.  Now
> his K3 has no RX at all.  I thought there was a high power protection
> circuit?  We have other rigs to use but any input as to what needs to be
> done with the smoked K3 would be appreciated before he sends it back to
> Aptos.

Bill,

I'm sure this will generate a flurry of responses without asking important 
questions. :-)

How far apart were the antennas, and how well were the antennas constructed 
and installed?

The how far apart thing is easy. The more complicated and important thing is 
the installation. If they didn't suppress common mode from the antennas, you 
could have direct RF excitation coming through wiring to a common generator. 
If the antennas were next to each other, then you could have direct 
coupling. Even feedline lengths, because it affects current and voltage on 
bands where the feedline is mismatched, can have a huge impact.

Also, some antennas respond much better to out-of-band signals than other 
antennas do.

To give you an example of how immune the K3 is to problems, I have several 
antennas within 1/2 wave of each other and have no issues at all with the K3 
on one and 1500 watts on the other antennas. But.......these are planned 
antennas that have reasonable band-selectivity. I don't do anything foolish.

At field day, I have never operated without a bandpass filter on my rigs. 
As a matter of fact I keep two or three old Johnson KW matchboxes around for 
just such occasions.

I made some measurements in my K3 and antennas because I had an unexplained 
failure in the post mixer amplifier. (This had NOTHING to do with RF levels, 
it was a new operation failure when I first connected the K3 by itself.) 
Current can get pretty high in that device when input level goes over 10-20 
dBm. The mixer is tough and just passes the input signal right through!

I'm not sure what the most common failure is, but when I looked at mine the 
device following the mixer seemed to be the thing that got hottest fastest. 
Of course with a very high quick spike, damage could be almost anything near 
the front end.

Bottom line is if an extra 10 dB from an amp caused the K3 to fail, the 
system was not planned very well. You should have a hell of a lot more 
headroom than 10 dB below catastrophic failure in a good installation, so it 
might have ate the K3 up anyway over time at 100 watts!

73 Tom