Bob The idea of a balun is to provide balanced drive to the transmission line so that it will not radiate, saving that for the antenna. Part of the idea is to reduce TVI etc due to feedline radiation, and part is to preserve the directivity pattern of the antenna. A radiating feedline tends to an omnidirectional pattern, spoiling a good directional antenna pattern.
Out in thw boonies, this is a nonissue, as you want to raidate anywhere you can. Just go out and enjoy. 73, Bob N6WG -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Bob Cunnings Sent: Monday, August 08, 2005 9:30 AM To: Elecraft Subject: Re: [Elecraft] ATU efficiency and the Elecraft T1 So far I've not bothered with a balun when running my KX1 into a dipole fed with balanced line (using the internal tuner to match) and seem to have pretty good results, better than the random wire and counterpoise so far (portable operation over poor ground). My thinking was that since the whole system is floating with respect to ground (I'm usually sitting on a slab of rock), it wouldn't really matter. I find little in the literature about this topic, except older references to "floating" single ended antenna tuners to drive balanced lines. I certainly understand the necessity of the balun when the single ended output is truly ground referenced via a good ground system, etc. Whats the truth? Bob NW8L On 8/8/05, wayne burdick <[EMAIL PROTECTED]> wrote: > Jay wrote: > > > All tuners will eat up some percentage of your RF output power. > > The ones with toroid or smaller inductors may eat up more power. > > Jay, John, etc.: > > The physical size of the inductors would only be a factor if they were > also inefficient (dissipating a lot of heat). In all of our tuners, > including the T1, we use high-Q toroidal inductors with core and wire > sizes appropriate for the intended RF current. In addition, we use > high-Q capacitors (NP0/C0G ceramic or in some cases silver mica). > > In lab tests of the T1, I used loads from 3 to 1000 ohms, calculating > the power into and out of the L-network. The T1's efficiency was on a > par with other tuners of this type, including those with much larger > toroids. For typical matches, losses range from 0.1 to 1 dB. A tuner > using very large air-wound inductors and air-variable capacitors might > cut these values in half, and would have an advantage at very high or > low impedances. But such a unit would also not be very portable, so > it's a tradeoff. > > A much bigger factor in most antenna installations is ground loss, > which usually dwarfs any L-network losses. This is especially true of > portable antennas. If your goal is to radiate the best possible signal, > you can reduce ground losses by using *lots* of radials, or consider a > dipole or inverted V with its feedpoint as high off the ground as > possible. > > When I'm in casual operating mode I simply toss a wire in a tree, lay > out one radial, use no feedline at all, and accept the inevitable > ground loss. If I'm "serious," I string a wire between two trees such > that the center is 20 to 30 feet high, feed it with 300-ohm low-loss > twinlead, and use a low-loss balun between the feedline and the tuner > (the Elecraft BL1 is quite small and works well in this application). > In this cases I use a wire that's at least 1/2-wavelength long on the > lowest band of operation. > > The T1 finds a low-SWR match on most or all HF bands with either > "casual" or "serious" antennas :) > > 73, > Wayne > N6KR _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net 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 _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net 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
