Are you keeping your antennas grounded when they are not in use? It does not take low humidity or wind or rain or snow to put an electric charge on your antenna if it's well insulated. The action of the earth's atmosphere maintains a huge charge between the ionosphere and the ground - almost 400,000 volts - in spite of a constant leakage current through the atmosphere from the ionosphere to ground of over 1,500 amperes. Near the ground the voltage gradient is close to 100 volts per yard of altitude. Given some time, depending upon the number of free ions in the air, an insulated antenna will lose electrons until is develops the voltage associated with its height above ground. And then, "pow" when you connect the antenna to a piece of equipment and electrons from the earth rush in. The amount of current is proportional to the mass of the insulated antenna.
Nowadays any metal high above the ground in buildings is connected to an earth ground, but in the past that was not always so, and workers were occasionally shocked when they touched metal even on a dead calm day. At least one Ham, troubled by almost constant high-level popping QRN, finally traced the source to a large copper cupola roof on his home that was not grounded. At night, he could see occasional flashes of sparks from the roof to nearby grounded metal even though the air was still. Bonding them together fixed it. Usually these currents are so small that you are not aware of them, but the voltages can be enough to puncture sensitive semiconductor gates and junctions. The most sensitive areas in most rigs are in the diodes used in the SWR bridge at the antenna jack or in diodes used in T/R switches. Other semiconductors in a typical rig may be more sensitive to damage, but they are well protected by the intervening circuits between them and the antenna connector that provide a d-c path to ground. If an antenna has been left floating, connect it to an earth ground for a moment before you connect it to the rig. Good quality antenna switches provide a d-c path to bleed off the charge as it accumulates. The KAT500, for example, provides such a d-c ground path whenever it is turned off and for any antennas connected that are not in use. 73, Ron AC7AC -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of John K3TN Sent: Friday, February 22, 2013 5:45 AM To: [email protected] Subject: [Elecraft] K3, KPA500 - PIN Diode Failure in KPA When K3 Subrx Turned on During Xmit? Here's the set up: K3 to KPA500 to KAT500, all Aux bus connections. Began to have high attenuation on receive when the KPA500 was turned from STBY to OPER. Determined by Elecraft to be a blown PIN diode, which makes sense. But why did the PIN diode blow? Could be that it just failed, could be I mistakenly QSYed and transmitted with KPA at high power before KAT was tuned for new band. But I also remember this scenario happening a few times before I noticed the RX attentuation: Running N1MM software in a CW contest. I was transmitting some N1MM message and while transmitting went to hit the ESC key to do something and instead hit the ` key, which in N1MM turns on the sub-RX in the K3. In the heat of a contest exchange, hard to remember exactly what happened but I think that did cause a hard fault with the KPA. Not long after that the PIN diode was blown. Craig, the guy who repaired my KPA, said he didn't see how an inbound SUBRX ON command to the K3 while transmitting cause lead to a condition where the K3 is transmitting into the KPA while the KPA is in RX mode, but I'd figured I'd cast a wider net to see if it triggers any possible thoughts. I'm also cross-posting to the N1MM reflector. John K3TN ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
