A different approach that is often very effective is to use a separate on-ground antenna for receiving! QRN is greatly attenuated at ground level, much more than signals arriving from overhead. So, while the overall signal levels are much lower at ground level, the signal to noise ratio is greatly improved!
Such antennas are terrible radiators, so you need a rig that can provide an independent antenna input for receiving. The K3 and K3 provide for separate receiving antennas. On-ground antennas typically show 15 to 20 db lower signal levels than in-air antennas. That's over 3 S-units, but it's easily made up for by the low-noise preamplifiers in the Elecraft rigs. One common form for such an on-ground antenna is to use some 50-ohm coaxial line. Put it on the ground (or bury it, but if you do that it's smart to put it inside a plastic pipe to keep rocks in the soil from pushing on the coax until they break through the jacket). The coax can be any length but, as you might guess, longer is better. (Extreme lengths of several wavelengths laid out in a straight line will show directivity, just like a long-wire in the air). You can either short the far end of the coax or you can terminate the far end with a 50-ohm resistor. If you short the far end you need to make sure the coax is *not* electrically a 1/2 wave (or multiple thereof) long. That's because a half-wave line repeats the impedance at the far end at the rig. If you have far end of an electrically half-wave line is shorted, you'll see a "short" at the rig! That's not a concern with a 50-ohm termination at the far end. Doug DeMaw, W1FB (SK) made a cheaper version from two-conductor "speaker" wire that he said worked very well. Probably any weatherproof "zip" cord would work. He found a terminating resistor of about 210 Ohms worked nicely and he used a balun at the rig end to remove common-mode signals flowing along the two conductors. A length of coax connected the balun to his rig. Ron AC7AC _______________________________________________ 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
