[Elecraft] K3, KPA500 - PIN Diode Failure in KPA When K3 Subrx Turned on During Xmit?

[hawley, charles j jr]

My antennas are always dc grounded and i lost a pin diode.


Sent from my iPad
Chuck, KE9UW 
(Jack for BMW motorcycles)

On Feb 22, 2013, at 12:12 PM, "Ron D'Eau Claire" <ron at cobi.biz> wrote:

> 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: elecraft-bounces at mailman.qth.net
> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of John K3TN
> Sent: Friday, February 22, 2013 5:45 AM
> To: elecraft at mailman.qth.net
> 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
> 
> 
> 
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