OK a bit of explanation is in order. The K2 (and K3 as well as the K1) control power based on measuring the actual output power and adjusting the drive to provide the requested power level. That means a device capable of measuring the RF output is necessary. Well, that is the wattmeter in the KPA100 - it uses Schotky 1N5711 diodes because those have been chosen to provide the best response with respect to frequency and power level.
Yes, those diodes are a bit "tender" with respect to static. Those diodes live right at the antenna terminals and are quite susceptible to static charges. The K2 (K3) power control system will give you the most consistent power control (because it is a closed loop), but to operate, it must be able to measure the output power. and the diodes that do that task are susceptible to static discharges. Yes, go out and find yourself some resistors between 22k and 100k and connect them across your feedlines. Note that I do not care about the path to (earth) ground - while that may be nice, IMHO it will not help with the equipment damage from antenna induced static charges. Yes, the station should be connected to earth ground, but for purposes of lightning protection rather than static discharges from antennas. There are 3 grounds in a ham station - AC safety ground (see NEC requirements), Lightning safety grounding (see Ron Block's papers at Polyphaser,.com) and RF ground. The RF ground is the most elusive, because it does not include any hard connection to mother earth. "Ground" in this sense is a point of commonality, or a point where the RF voltage is zero. That condition occurs at the feedpoint of a balanced antenna - the zero voltage point directly between the feedpoint terminals. OK, I am mixing a bit of the theoretical and the practical, but take to heart, it is not hard. When the wavefront moves from the feedline into the antenna, the conditions change from conduction (obeying Kirchoff's laws) to radiation (obeying Maxwell's wave equations). Where the transition point occurs is indeed a mystery. That has nothing to do with the "ground question".. Everything needs to have a return path, and I believe that is valid for RF as well as for DC conditions. This is the Kirchoff stance,, but there are those who argue than the Maxwellian equations offer a better explanation. That may be true, but there is little difference. My goal is not to "solve" this inconsistency, but just to add a bit more information (OK, to justify my conclusions be they right or wrong). 73, Don W3FPR On 9/8/2012 10:07 PM, stan levandowski wrote: > Thanks, Don. I have a homebrew doublet with a gas discharge center > insulator and I have been under the (apparently incorrect) assumption > that I've been well protected from static buildup. I've also got a > coaxial switch which is dialed into the dummy load when not in use. > > Guess, I better go out and buy a 22K resistor now and fnish the job ;) > > Appreciate the tip. > > 73, Stan WB2LQF > > > On Sat, Sep 8, 2012 at 9:17 PM, Don Wilhelm wrote: > > >> >> The Gas discharge tubes are effective against large charges - the >> ones I have will squelch a voltage in excess of 600 volts, but below >> that level, they will do nothing. That 600 volt surge is enough to >> take out the diodes in the K2 KPA100. The K3 has more protection. >> but still should not be trusted when it comes to static charges. >> > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
