+++++++++++++++++++ Reply-To: From: "Ron D'Eau Claire" To: "'Lloyd Lachow'" , , Subject: RE: [Elecraft] Twinlead feedline to my K1 Date: Fri, 19 Jul 2002 08:34:54 -0700 I'm cornsiderating upon putting up a NB6Zep antenna ( http://home.teleport.com/~nb6z/nb6zep.htm ), and I'm not sure how to connect the twinlead to my K1, which has an internal autotuner... 73/72/oo, Lloyd, K3ESE As the web site mentions down near the bottom, the easiest way to connect the feeder to an "unbalanced" output like your K1 is by using a "balun" or "balanced to unbalanced" transformer. The NB6Zep is a conventional "doublet" fed at the center with open wire line. Many Hams refer to these antennas as dipoles, although "dipole" usually refers to an antenna that is 1/2 wavelength long. Using a balun at the transmitter will provide balanced" push-pull" currents for each side of the feed line. That will minimize radiation from the feed line, because the r-f fields created by each wire in the feeder will cancel each other out. That means that virtually all of the radiation will take place from the horizontal wire up in the clear. You can buy baluns from many sources and instructions for making your own are in almost any book on ham antennas. On line check out http://www.hard-core-dx.com/nordicdx/antenna/feed/4_1balun.html or http://www.bytemark.com/products/kit_bal1.htm. I got these with a quick peek with an internet search engine. If you search on "balun" you'll be inundated with info! Keep in mind that baluns are used in many places, not just transmitters. You want a "transmitting" balun, not one designed for television or some other small signal use. With this type of antenna, the impedance at the balun will vary widely over the various bands and r-f voltages and currents can be very significant, even at QRP power levels. Be sure to keep the feed line away from objects, especially any metal. A distance of 2 or 3 times the spacing between the feedline wires is usually adequate. Ron AC7AC K2 # 1289 ++++++++++++++++++ Date: Fri, 19 Jul 2002 11:34:37 -0500 From: "George, W5YR" Organization: AT&T WorldNet Service To: rondec at easystreet.com Cc: 'Lloyd Lachow' , fpqrp-l at mpna.com, elecraft at mailman.qth.net Subject: Re: [Elecraft] Twinlead feedline to my K1 Just a tack-on comment since Ron didn't mention this point: In an installation of this sort, a 1:1 current or choke balun will generally prove more successful than a 4:1 current or voltage balun. The input impedance of the twinlead will swing wildly over the different bands and on some bands a 4:1 balun will just make things a lot worse than they already are. Occasionally it can work the other way, but it seldom seems to happen very often. The 1:1 baluns operate independently of the line input Z and frequency whereas the 4:1 transformer action is highly dependent upon frequency, load, etc. The 4:1 voltage balun was once the workhorse but it has fallen from favor as its shortcoming were discovered. The current balun is now to be preferred, and the 1:1 version appears to work best in your application. 73/72/oo, George W5YR - the Yellow Rose of Texas Fairview, TX 30 mi NE of Dallas in Collin county EM13qe Amateur Radio W5YR, in the 56th year and it just keeps getting better! QRP-L 1373 NETXQRP 6 SOC 262 COG 8 FPQRP 404 TEN-X 11771 I-LINK 11735 Icom IC-756PRO #02121 Kachina 505 DSP #91900556 Icom IC-765 #02437 +++++++++++++++++++ To: Lloyd Lachow Cc: Elecraft at mailman.qth.net Subject: Re: [Elecraft] Twinlead feedline to my K1 From: "Steve Lawrence" Date: Fri, 19 Jul 2002 14:11:50 -0400 Lloyd, In the spirit of kit building and home brew, you might check out the high-performance balun kit offered by NJQRP.... http://www.njqrp.org/balun/index.html The balun (short for "balance to unbalanced" where twin-lead, and ladder-line are inheritantly balanced, while coax is unbalanced) will match the unbalanced currents out of the K1 tuner, to the balanced load of the twin-lead fed dipole. There are those that argue a balun is unnecessary, and that an antenna/feed line/tuner system will work well without it. I would try just connecting one lead to the red post and one to the black post of your K1 and see if it tunes up! You may be pleasantly surprised. 73, Steve aa8af ++++++++++++++++++++ Reply-To: From: "Ron D'Eau Claire" To: Subject: RE: [Elecraft] Twinlead feedline to my K1 Date: Fri, 19 Jul 2002 11:44:52 -0700 There are those that argue a balun is unnecessary, and that an antenna/feed line/tuner system will work well without it. I would try just connecting one lead to the red post and one to the black post of your K1 and see if it tunes up! You may be pleasantly surprised. 73, Steve aa8af Yes, that often works and works VERY well! However, parallel wire feeders like twinlead or open wire lines will radiate a great deal unless the currents are balanced. Also, they pick up r-f all along the length of the feeder when they aren't terminated in a balanced load at both ends. Many "windoms" and other off-center fed antennas count on the feeder radiating and picking up signal for part of their performance. If you are going to let the feeder be unbalanced and radiate, treat it just like your end-fed wire. Keep it in the clear, get it up as high as possible and in the clear as quickly as possible, and be aware that everything near it will absorb some r-f. Also, any sources of noise (motors, computers, etc.) near the feeder will add QRN to the signals. Ron AC7AC K2 # 1289 ++++++++++++++++ From: "Sandy, W5TVW" To: "Lloyd Lachow" , , Subject: Re: [Elecraft] Twinlead feedline to my K1 Date: Fri, 19 Jul 2002 09:34:44 -0500 Try connecting it right across the output of your BNC to binding post adapter! The KAT1 will probably tune up fine with it. If not, you may have to go to a 1:1 or 4:1 small toroidal balun to make it tune on all bands. I have a big 80 meter center-fed Zepp I use with it fed with a 120' run of 450 ohm ladderline. It will get a bit flaky on 15 meters from time to time. 40-20 always OK. Gets out just fine! Don't be afriad to experiment with the K1-KAT1 combo! 73, Sandy W5TVW ++++++++++++++++++ Date: Sat, 20 Jul 2002 08:57:20 -0600 From: "James R. Duffey" To: Cc: Subject: [Elecraft] Balun for K-1 I would sugest using an air wound coax choke balun. THe HAndbook and ANtenna BOok should tell you how to make one. For the 7MHz to 21 MHz range of the 4 module K-1 I would suggest 10 ft of RG-58 wound into 7 turns or so. Connect it like regular coax on the transmitter end, and connect the shield to one side of the feed line, and the center conductor to the other side. - Dr> Megacycle KK6MC/5 -- James R. Duffey KK6MC/5 Cedar Crest, NM DM65 +++++++++++++++++++++ Date: Sat, 20 Jul 2002 11:46:03 -0600 Subject: Re: [Elecraft] Balun for K-1 From: "James R. Duffey" To: Tom Hammond N=?ISO-8859-1?B?2A==?=SS Cc: Tom - I am familar with this work, and have often quoted it in the past. It is a definitive work. I think it is unecessarily complicated for the task at hand. For the use over the short frequency span of interest to a K-1 4 band module user, 7 MHz to 21 MHz, a simple coiled coax choke balun, 6 or 7 turns should provide adequate choking reactance. It is simple, can be made in minutes, and is effective. With it you can be on the air in minutes. The numbers you quote indicate the effectiveness of the simple coiled balun, the balun in column 5, 8 turns sceamble wound into a 6 5/8 in coil, has a peak choking reactance of 8530 ohms and a 200 Ohm choking reactance bandwidth (recommended by deMaw) from 2 MHz to 16 MHz (an 8:1 bandwidth. There are those who think a 200 Ohm reactance bandwidth is inadequate, so the 500 Ohm choking reactance bandwidth is from 3.5 MHz to 10.5 MHz, still a respectable 3:1 ratio. Winding a coiled coax choke balun as I suggested should be adequate for the 4 band K-1, which was the application I was addressing. Other applications may require more care. and a better balun. When improvements are made to the antenna system at a later time, the balun can be upgraded. But to get on the air quickly with a minimum of fuss and acceptable performance, the coiled coax balun is hard to beat. The posting was in keeping with my QRP KISS (Keep it simple stupid) policy. I find the KISS policy keeps me out of trouble and on the air more than pursuing optimum (and oftem more complicated) solutions. Don't get offended, the stupid in KISS is not meant to apply to anybody but me. - Dr. Megacycle KK6MC/5 -- James R. Duffey KK6MC/5 Cedar Crest, NM DM65 +++++++++++++++++++ Date: Sat, 20 Jul 2002 16:07:27 -0500 To: "James R. Duffey" From: Tom Hammond =?iso-8859-1?Q?N=D8SS?= Subject: Re: [Elecraft] Balun for K-1 Cc: Hi Jim: >I think it is unecessarily complicated for the task at hand. For the use >over the short frequency span of interest to a K-1 4 band module user, 7 MHz >to 21 MHz, a simple coiled coax choke balun, 6 or 7 turns should provide >adequate choking reactance. It is simple, can be made in minutes, and is >effective. With it you can be on the air in minutes. The numbers you quote >indicate the effectiveness of the simple coiled balun, the balun in column >5, 8 turns sceamble wound into a 6 5/8 in coil, has a peak choking reactance >of 8530 ohms and a 200 Ohm choking reactance bandwidth (recommended by >deMaw) from 2 MHz to 16 MHz (an 8:1 bandwidth. There are those who think a >200 Ohm reactance bandwidth is inadequate, so the 500 Ohm choking reactance >bandwidth is from 3.5 MHz to 10.5 MHz, still a respectable 3:1 ratio. >Winding a coiled coax choke balun as I suggested should be adequate for the >4 band K-1, which was the application I was addressing. Other applications >may require more care and a better balun. When improvements are made to the >antenna system at a later time, the balun can be upgraded. But to get on the >air quickly with a minimum of fuss and acceptable performance, the coiled >coax balun is hard to beat. I agree completely with your response! I was mainly posting the article for the benefit of all of us on the reflector, rather than directing it at anyone is particular. Of course, MANY (thousands, I'm sure) scramble-wound baluns have been made over the years (my tribander sported one for probably 15-18 years itself). And we never knew the difference between the way it worked and the way it might have performed had it been wound in a solenoidal fashion. Heck... we STILL don't now... But, thanks to the article, I now know that if I want to obtain PEAK performance from my coaxial-cable baluns, I should probably wind them in a single-layer coil, rather than in the manner I'd been using for many years. As you state, in many instances a single-layer coil is not required to obtain more than adequate performance. >The posting was in keeping with my QRP KISS (Keep it simple stupid) policy. >I find the KISS policy keeps me out of trouble and on the air more than >pursuing optimum (and oftem more complicated) solutions. Don't get offended, >the stupid in KISS is not meant to apply to anybody but me. I'm not offended in the least... and I do appreciate your further discussion (above) of the subject. Thanks for taking the time to respond. And, don't worry, MOST CERTAINLY applies to me very well...!! 73, Tom Hammond N0SS +++++++++++++++++