+++++++++++++++++++++++++++++++++ See also "Balun_Notes" in this directory +++++++++++++++++++++++++++++++++ Date: Tue, 17 Jul 2001 14:27:22 -0400 From: "Steve Lawrence" Subject: RE: [Elecraft] Balun for KAT1 Because of the issues associated with a transformer based balun, I decided upon using a W2DU style choke type balun for my portable operation. While typically available at only a 1:1 ratio, I reasoned the main purpose was to keep stray RF out of the tuner and off of the K2 chassis -- let the tuner provide the match to the load not a transforming balun. I built the balun from a kit from "the wireman" (www.thewireman.com) and purchased at the Dayton Hamventon. The kit consists of about 1 ft. of Teflon insulated coax (RG303U), and 50 ferrite beads -- an over design for QRP as it will handle 1KW. I mounted the ferrite bead covered coax in a box and fitted a BNC input and banana jack output (to a ladder line fed dipole). The balun went between KAT2 tuner and antenna feedline. While tested satisfactorily in portable operation, I have no way of measuring losses or effectiveness. I made a dozen SSB contacts into Europe on my K2 during the weekend on the 40M dipole up about 20 ft. It's not the smallest/lightest solution, but ultimate portability wasn't the goal (it is smaller than the typical 1KW toroidal based balun however). If I could come up with a smaller/lighter design better suited for QRP power levels, so much the better. Better still... a multi-band antenna design that doesn't require a balun. But those experiments remain to be done here... sometime... 73, Steve aa8af K2 #2033 +++++++++++++++++++++++++++++++++++ "Ron D' Eau Claire" Sent by: owner-elecraft at qth.net 07/16/2001 02:16 PM Please respond to "Ron D' Eau Claire" To: cc: Subject: RE: [Elecraft] Balun for KAT1 Greg, KI8AF asked: >Does anyone have a really simple plan for a > balun. > Presently have the 40 and 20 band filter but plan to expand to maybe > 30 > and 17 in the futrue. Would be nice to have a very small, portable > balun > to cover these bands. Asking to much?? It's no trick to build a balun that will cover 1.8 to 30 MHz and work well. Baluns are quite broadband when used properly. What they do NOT do well is handle extreme impedances. Virtually every balun you will encounter from normal sources is designed to look into a 50 ohm non-reactive load on one side, and either 50 or 300 ohms non-reactive on the other side. That means they are used in a feeder with a very low (1:1 ideally) SWR on it. "Non-resonant" antennas with so-called 'tuned' feeders tend to present extreme impedances to the balun on one band or another, depending upon their size. You can get away with using a balun with higher SWR's. It depends upon how high the SWR gets. At some point the balun starts acting more like a dummy load than a balun, and your rig will seem to be happily feeding power into the antenna, when it is actually feeding power into the balun-dummy load. That said, many operators, including me, have done it and gotten away with it. It's a bit hard to predict just what will happen at higher SWR's and it's not easy to know how efficiently the balun is working. If the balun starts arcing or if it has a torodial core and that gets hot or breaks, you can be sure the balun is being misused. Unfortunately, you can throw away virtually all of 5 watts in a balun and never know it. That's not normally enough to make them arc or fracture a core. Probably the best practice is to use the most robust balun you can lay your hands on. A big core will handle larger magnetic fields produced by high currents in the windings better, and the bigger spacing of turns and better insulation will help avoid leakage losses when the voltages are high. Amidon makes a nice balun "kit" that sells for less than $10. See http://www.bytemark.com/amidon/kit_bal1.htm for more info. You will notice that it is rated for a kilowatt. That's assuming it is used in a FLAT feedline (1:1 SWR). It probably represents a good investment in capacity if you are going to use it with an ATU feeding some sort of tuned feedline. The kit consists of a toroidal core about 2 inches in diameter, some heavy duty magnet wire to wrap on it and instructions. Personally, I'd avoid a balun in the field if I could. Use an end fed wire against a 1/4 wave 'counterpoise' connected to the case or a simple dipole. Since the K1 is a two-band rig, two dipoles, one for each band, connected to the same feedline would probably be my first choice. While that works 'best' if the bands are harmonically-related (say 40 and 20 meters) you can still use that trick on just about any set of bands you choose. You can even make the radiator out of a half wave of twin lead, cutting the second wire short to make a 1/2 wave for the higher-frequency antenna. That way you only have to string up one 'radiator'. The SWR on the feedline will be significant, but if you use good feedline (no tiny RG-174) the losses in a reasonable length won't be great and the K1's ATU should be able to tune it easily. You can even go to four bands that way, if you are willing to deal with two lengths of twin lead each containing two radiators, or you might have two antennas matching the band pairs you choose. Ron AC7AC K2 # 1289 ++++++++++++++++++++++++++++++++ Date: Thu, 19 Jul 2001 12:03:16 -0500 From: "benlightnd1" Subject: [Elecraft] A neat little balun For those of you who are questioning what you will use as an antenna in the field and think you may need a balun, check out Jameco's catalog ( page 61 ) or go to their home page and type "balun" or 72637 into their search engine. This is a small balun that converts BNC connectors to ladder line with a 100 ohm termination. weight is 0.1 lbs. Might be just what you need!! The only problem with this one???? You didn't get to build it!! Hee Hee 73 to all Jerry N0JRN ++++++++++++++++++++++++++