On Thu, 2 Dec 2004 12:07:06 -0800 (PST), Lee Buller wrote: >I think you have way to much RF in the shack if there is no trouble with the >system when you have a dummy load hooked up.
Yes, I do have a lot of RF in the shack -- note the description of the antenna. It's essentially an end-fed wire that works against "ground," so it MUST put a lot of RF in the shack if it is going to work. In my case, "ground" consists of five driven rods, a dozen radials of various lengths, and a big wrought iron fence (roughly 135 linear feet) that runs around the front of my city lot. All of this is bonded together on a big bus bar a 6" below the operating desk, and bonded to each radio, the amp, and the antenna tuner with 1" wide tinned copper braid. But radio gear should reject that RF if it is built properly. When radio gear has a problem with "RF in the shack," a common cause is what in the pro audio world we call a "pin 1 problem," which is a mis-termination of the shields of input and output cables. A shield SHOULD go straight to the chassis of a radio (like a BNC or SO239 mounted to the chassis). Unfortunately, several decades ago it became standard practice to cut corners by mounting connectors to the printed circuit board and connecting the circuit board to the chassis with mounting screws. This is "the pin 1 problem." Why is this construction a problem? Simple. RF current flows on that cable (you call it a mic cable, but mother nature knows that it's an antenna). That RF current flows along circuit board traces to get to the chassis and to "ground" or whatever completes its return path. Those circuit board traces have inductance, so there will be an IZ drop across it due to the current flow. And that RF will get impressed on various parts of the circuit, depending on where the circuit board layout puts it. The K2 has a pin 1 problem at the mic connector and the headphone connector -- neither of those connector shells touch the chassis if built according to instructions. I suspect that there is also a pin 1 problem at the RS232 connector, but haven't looked at that yet. I've fixed the pin 1 problem at the mic connector. BTW -- lots of ham gear has pin 1 problems, including all the TenTec gear I've looked at. Thanks to those who have responded re: instability in the K2/100 power amp stage. All ideas are appreciated. Jim Brown K9YC _______________________________________________ Elecraft mailing list Post to: [email protected] 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.htm Elecraft web page: http://www.elecraft.com
