RE: [Elecraft] An Antenna for the BL2 Balun
Jim, N2EY wrote: I'm highly skeptical of *any* simple wire antenna that claims multiband performance without a tuner or tuner-like device. And so am I. In this case it's rather like the trick of feeding a 40 meter dipole on 15 meters where it's 3/2 waves long. The SWR is adequately low for use with little or no correction from a tuner. The antenna mentioned sounds like the one developed by Bill Wright, G0FAH who says he came up with a combination of radiator and open wire feed line that will have low reactance (be self resonant) on 40, 20, 15 and 10 meters. However, the impedance at the feed point will be close to 200 ohms on 40, 20 and 10 meters and about 50 ohms on 15 meters. So Bill used a switchable balun that selects 4:1 on 40, 20 and 10 meters and 1:1 at 15 meters. There are three advantages:: 1) The balun is operating at a low SWR to avoid excessive losses and it should behave predictably, 2) No tuner is required for most rigs, and 3) The low SWR on the coax means any length within reason can be used with low losses The dimensions of the antenna are critical! As the original poster said, he changed the length of the open wire line section. That means he simply has an off-center-fed wire. Any advantage provided by Bill's design to provide a low SWR at the balun and on the coax is lost. The dimensions Bill gives for the antenna are as follows: Short leg of the radiator is 23 feet and the long leg is 46 feet. Using 450 ohm ladder line, he recommends either 55 or 111 feet. This dimension is very important as the line acts as an impedance transformer. The balun goes at the end of the ladder line and the coax feeding the balun can be any convenient length as the SWR is (supposed to be) very low on those bands if the balun is switched for a 1:1 impedance transformation on 15 and a 4:1 transformation on 40, 20 and 10 meters. Of course, on 30 meters (or any other band) the antenna simply becomes an off-center-fed doublet in which the whole system, including the balun and coax will see high SWRs and the attendant losses. I believe this antenna first appeared on the "Yankee side of the pond" at least in QST for February 1996 Ron AC7AC ___ 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
Re: [Elecraft] An Antenna for the BL2 Balun
In a message dated 12/2/06 8:58:34 AM Eastern Standard Time, [EMAIL PROTECTED] writes: > a 69-foot antenna with the feedpoint 23 feet from one side and 46 feet > from the other. From the antenna to the balun is either 55 or 111 feet of > 450-ohm line, or, 50 or 110 feet of 300-ohm line. From the balun to the rig > > is any length of 50-ohm coax. > > For 40, 20, and 10 meters, the balun is 4:1. For 15 meters, the balun is > 1:1. According to the article, no tuner is needed. I'm highly skeptical of *any* simple wire antenna that claims multiband performance without a tuner or tuner-like device. Doesn't mean the antenna's no good, just that it probably doesn't present 50+j0 on all the bands it covers. It probably comes close enough that the SWR is under 3:1, which can be matched by many rigs without a tuner and by practically any rig with a tuner - even if the tuner has limited range. Also means the coax won't have much loss. > > Since the BL2 has a switch for 4:1 or 1:1, this may be an application > without an antenna tuner. > > There is no mention of 30m, so that is an unknown. On 30 meters the antenna isn't resonant, and the feedpoint Z will be reactive. This antenna is just a version of an off-center-fed dipole. No better nor worse than any other dipole. What I like is the simplicity, light weight (the balun isn't up in the air) and the fact that if you need a long feedline, much of it can be balanced open-line, with a short piece of coax to come into the shack. It occurs to me that a double-sized version (138 feet long, feedpoint 46/92 from the ends, with feedline 110 or 222 feet long (450 ohm) or 100 or 220 feet long (300 ohm) would cover 80, 40, 30, and 20 meters, with the balun being 4:1 on 30 meters. The dimensions would almost certainly need some fussing with, but I would not be surprised if a set of lengths could be found that would do the job. If I only had the space! 73 de Jim, N2EY ___ 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
Re: [Elecraft] An Antenna for the BL2 Balun
John, I put up one of these for my father N5LK, up 25' in the center and 30' on one end. I dint use the specified length of ladder line, just 450 ohm window line of a convenient length. His K1 tuned it a little roughly on 17m but it works FB there anyway. If I had had more time I would have changed the feedline length. I used a 1:1 balun, the BL1. From his QTH in MS I worked K1ZZ Dave, and then a station near my house in California on 20m. Once I got back, we had no trouble working each other on 40, 30, or 17m. 73, Leigh/WA5ZNU On Sat, 2 Dec 2006 5:58 am, John Meade wrote: I was reading the ARRL's "Wire Antenna Classics" and noticed an interesting antenna (not that all of them aren't interesting hi hi). This was an article by G0FAH called "Four Bands, Off Center" (p 1-13, also from QST, Feb 1996). It is a 69-foot antenna with the feedpoint 23 feet from one side and 46 feet from the other. From the antenna to the balun is either 55 or 111 feet of 450-ohm line, or, 50 or 110 feet of 300-ohm line. From the balun to the rig is any length of 50-ohm coax. For 40, 20, and 10 meters, the balun is 4:1. For 15 meters, the balun is 1:1. According to the article, no tuner is needed. Since the BL2 has a switch for 4:1 or 1:1, this may be an application without an antenna tuner. There is no mention of 30m, so that is an unknown. Another unknown might be the matching with respect to height above ground. By the way, I bought a blank BL2 PC board and switch from Elecraft and made my BL1 into a switchable 4:1 or 1:1 balun. 72, John W2XS K2 #1116 KX1 #15 ___ 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
