Re: long wire


K9NUD-Steve
 
Edited

Mike, there’s a lot of confusion about long wire antennas. Many consider an end-fed half wave (typically using a 49:1 or 64:1 transformer) to be a long wire. That’s technically not true. A long wire is deliberately non-resonant, since resonance on any band would result in an unacceptable high impedance. That’s where the EFHW works best, as the transformer can deliver something closer to 50 ohms to the radio.

A true long wire is typically used with a 9:1 un-un transformer. If the length of the wire is not resonant, the resistance will be closer to 500 ohms. A 9:1 transformer can get that much closer to 50 ohms on several frequencies, leaving a value that your internal tuner has a better chance to match.

9:1 end-fed long wire antennas must be designed to be non-resonant on all the bands you hope to use. The math isn’t too tough, and thankfully others have done it. There are several websites that mention the “magic lengths”, but most arrive at the same conclusion:  “The magic lengths to use with the End Fed longwire is 29, 35.5, 41, 58, 71 and 84 feet”

There are longer lengths as well. I just installed a 105’ inverted L with a 9:1 un-un. It seems to outperform my 6BTV and my EFHW, though the latter is not mounted as high. I’m currently experimenting with the transformer, comparing one with an iron core toroid versus a ferrite core. The ferrite is getting most of the desired bands closer to resonance. It definitely tunes easier, particularly on the low bands. I need to do more testing, and possibly add 19’ to the antenna to get to 124, another oft-mentioned length. 

I have used a 29’ vertical for portable ops with a 9:1 un-un mounted to the winder, along with a 16’ counterpoise. It performs quite nicely on 40M up. I run QRP and routinely work the whole country and plenty of Europeans on 20M. I’m eager to try is on higher bands as conditions improve. I’m also planning to add 25’ and run it as an inverted vee to see if I can use it on 80M.

I would encourage you to go down the 9:1 rabbit hole with gusto. You should also go down the EFHW rabbit hole too. Do yourself a favor and order a bunch of toroids such as the T130-2 for the 9:1 (http://www.earchi.org/92011endfedfiles/Endfed6_40.pdf) and a bunch of FT140-43’s, FT240-43’s for EFHW transformers. You might want to get some FT240-31 toroids too (useful for 1:1 current values). Have fun!

73 de K9NUD

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