Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!watmath!clyde!bonnie!akgua!sdcsvax!sdcrdcf!hplabs!sri-unix!jhs@Mitre-Bedford From: jhs%Mitre-Bedford@sri-unix.UUCP Newsgroups: net.ham-radio Subject: Re: antenna tuners for receivers. Message-ID: <12425@sri-arpa.UUCP> Date: Thu, 27-Sep-84 10:47:00 EDT Article-I.D.: sri-arpa.12425 Posted: Thu Sep 27 10:47:00 1984 Date-Received: Sun, 30-Sep-84 04:43:57 EDT Lines: 38 An interesting comment, that - it got me thinking! I had always assumed you cannot move the current distribution in an antenna by fiddling with a tuner at the feed point. For antennas terminating out there in an infinite impedance (the insulator at the end), this is indeed true: the current is always zero at the end and always has its maximum a quarter wavelength in from the end. No matter what you may do with a tuner in your shack. Or even a tuner up at the feed point! However, you have educated me to the fact that if you bring the end of the antenna back into the shack, as with a loop antenna, you can indeed hang non-infinite impedances on its end, and can therefore change the standing wave pattern. Certainly you can short the end, getting a current maximum at the shorted point. You can also leave it open, getting a current zero there as with the end fed antenna. Presumably you can hang other (complex) impedances there and put the current maximum anywhere you like. Neat. In particular, I agree that for a large loop (i.e. non-infinitesimal) this should make it possible to place a current maximum near the highest point on the loop. By reciprocity arguments one can see that this should indeed make the receiving loop perform better than it would otherwise. However, I still claim that for the "good ole" receivers at least, and at the lower HF frequencies, tuning the tuner will move the S-meter higher, but with a decent AGC the audio won't sound any different. I guess they don't build AGC circuits like they used to. (Gotta keep this controversy going somehow!) Somewhere between 20 Meters or so and 2 Meters, the SNR limit moves from external noise to front-end noise, and then I agree that the tuner is important. Of course it might be true that with the loop, changes in the directionality of the loop due to current distribution changes of the type conceded above might affect the signal to external noise ratio. Thanks for educating me to a phenomenon I was unaware of! -73, John Sangster, W3IKG