http://elecraft.85.s1.nabble.com/Prevent-Snow-Dirt-Static-damage-to-KPA100-after-upgrade-tp5666395p5666447.html
On Sat, 23 Oct 2010 16:07:41 -0500, "Kenneth A. Christiansen"
Thanks for that information Kenneth. I'll bet it works on Texas
>40 years ago we had a windy dust storm in Bismarck ND and I lost the RF
>amplifier in my new solid state Heathkit receiver three times that day
>before I realized the dirt and high winds were putting a static charge
>on my antenna. I found there was a capacitor between the antenna and the
>RF amp and the static would arc across the capacitor and burn out the
>RF amp. Of course tube type receivers did not have this problem. I found
>out a 100K resistor from the antenna to ground would prevent this and
>not load down the antenna.
>
>Several years ago my friend I each bought a new IC-746PRO. The first
>time we had a blizzard with 50 MPH winds and snow my friend and I both
>burned out our new rigs with snow static trying to check into the ND
>Weather Net. The K2 survived just fine. The IC-746PROs were both fixed
>under warranty but it still cost both of us shipping. I found out the
>IC-746PROs did not have any path to discharge the antenna charge from
>the snow static.
>
>I recently installed the KPA100 Upgrade and one of the steps was to
>remove R10 the 100uh choke between the antenna jack and ground. There is
>no other path to ground and I have read on the reflector about people
>having their SWR and Power measuring diodes go bad and it was easy to
>see why. I plan to use this rig to check into the ND Weather net this
>winter so knew I needed to fix the problem.
>
>MFJ on my remote tuner uses a 40 K resistor to protect their circuit.
>That is less than the 100 K I have used over the years so it should
>protect even better.
>
>I put in the following change to fix my problem. I bought four 10K half
>watt resistors in a package from Radio Shack for $1.99. I soldered them
>in series and soldered one end to the center pint of the antenna jack J2
>and the other end to ground. I calculate that the resistors would
>withstand a 16 to 1 VSWR and I do not think the KPA100 would be able to
>put out 100 watts to a 16 to 1 VSWR so the resistors should be safe. 40K
>should protect the diodes from any problem and under normal conditions
>should dissipate 0.2 watts.
>
>There is an easy way to protect the amplifier without making a
>modification to the amplifier it self. Buy a PL259 T adapter and a PL259
>plug. Solder one end of the 40 K series resistor to the center of the
>PL259 and the other end to the shell. The resistors can be covered by
>tape to prevent an accidental RF burn. Screw the PL259 /40K assembly to
>one side of the T adapter. Put the other two ports of the T adapter in
>series with the coax to the antenna or the coax to the 50 ohm side of a
>tuner.
>
>The one remaining precaution is to touch both sides of the antenna lead
>to ground just before hooking them up to discharge any static
>electricity on the antenna. This fix will not protect the equipment from
>a lightning strike but it does allow me to use my rig to check into the
>ND Weather net during a blizzard.
>
>I hope this can save someone else from having rig trouble after a high
>wind snow or dust storm.
>
>73 for now
>
>Ken W0CZ
>
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