First, thank you to those who responded and taught me the difference between these several types of diodes. Now, to share an experience, actually, several. three times in five years have had my radio go awry on transmit, and all three times the cause was the same; directional diodes in the SWR bridge.
Specifics of the symptom vary because, for example, this time in the K2, the FWD diode fried infinitely open in both directions, while the REF diode fried shorted. In the KPA both diodes fried leaving 1.5K in both directions.
Specific details of radio behavior were quite different, but general behavior, loss of the power control on the K2, HI CURR report from the radio trying to run all out (since the bridge is reporting inaccurately what power is going by it), unable to use the auto-tuner, inaccurate SWR and power out reporting.
KAT-2 ... not a recommendation, just a comment. I mount the diodes on the underside of the circuit board. This puts them on the outside of the KAT-2 module which makes it possible to replace them without any disassembly.
KPA ... I haven't yet thought of anything clever for making these diodes more accessible, would be nice.
Kirby, who really does know, suggests putting a 1 uh choke at the input of the directional coupler to protect these diodes. Once that is done, however, one will no longer be able to check the viability of the diodes while in the circuit since this will look like a short to ground to a DVM.
I am sure this problem occurs more or less frequently depending upon where one is located, and what kind of antenna. For example, I have never lost these diodes when using my forty meter full wave loop which puts the antenna at ground potential. Lost them now after putting up a G5RV flat top which seems to have no trouble gathering static even in a clear sky.
The KPA has a 100 uh choke across the antenna jack. That did not protect the diodes in the KPA, dunno why. I am sure it protects the finals.
P.S. Had a friend lose K2 finals to ESD. Is there any reason why one couldn't put that 100 uh choke across the antenna jack on the K2 f???
Thank you, and 73
Fred
kt5x
_______________________________________________
Elecraft mailing list
Post to:
[hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
http://mailman.qth.net/mailman/listinfo/elecraft
Help:
http://mailman.qth.net/subscribers.htmElecraft web page:
http://www.elecraft.com
Locked
