End Fed 9:1 Magic Wire Lengths

The end fed longwire has become a very popular antenna for field and portable use. I wouldn’t use one for my base station as the dipoles and verticals are the preferred way to go. If i have antenna restrictions then this antenna can help you get on the air and make contacts.

Due to the nature of wavelength and impedance at various frequencies there is a magic wire length to use for this type of balun. Remember, the 9:1 balun is doing a conversion of impedance from about 450-700 ohms down to 50 ohms. The antenna cannot be an actual 1/4 wave length on any ham band. Thus 8, 16, 32, 68 lengths are ruled out. For example a 32 foot length is actually a half wave on 20m with an impedance of about 3500 ohms and requires a 50:1 balun.

The magic lengths to use with the End Fed longwire is 29, 35.5, 41, 58, 71 and 84 feet

I use a 29 foot wire with my PackTenna 9:1 balun for 40m-10m and then add a 28 foot length for better coverage on 80m when needed.

5 comments

  1. Anthony · March 22, 2020

    Thanks for the consice info. As a newbie, it is easy to be overwhelmed.

    Like

  2. Seymour · December 29

    tnx ve3ips my call sign is zl2sy name Seymour. I like what you have written, precise and too the point, KISS (keep it simple Simon)

    Like

  3. Justin · April 1

    I built a 9:1 on a small FT50-61 and 28g magnet Wite. I put a 1K Ohm and an 820 Ohm resister in parallel to make 450 Ohms and attached it to the 2 terminal legs on the 450 Ohm side of the balun and connected the other 2 terminal legs of the 50 Ohm side to a coax and onto my Rig Expert and got a perfect 49 Ohm reading and flat SWR sweep from 1MHz to 55MHz. Then with the same material, I made a 1:1 common mode I3 choke. I ran a trace signal sweep through it from 1MHz to 55MHz and read 25bd of attenuation at 40 meters and the attenuation increased as you went up in frequency. The attenuation was not enough at 80m and 160m, not even close to the 20bd standard min.

    So there are 4 terminal legs on my 9:1 balun, 2 for the 450 Ohm side and 2 for the 50 Ohm side. I’ve never built an end fed, and I have no idea how to wire up the connection from the 9:1 balun, to the wire.

    Like

    • ve3ips · April 1

      Justin, I am sending a build article that will help you. The FT50 is probably too small and not one I have seen for this type of antenna but then the use case can be for QRP. I have seen some with the 80 size core but some builders said the efficiency was not that great. So far I have been using T130-6, T106-2 and T200 all red. Recent testing with this type of design is shwoing the 29 ft antenna to be best. I tried the longer 51-53 and the SWR on 40m was like 12 to 1. The 41 ft length also is very usable. Of course a tuner may be needed

      Like

  4. Steve K9NUD · July 11

    Thanks for sharing. I use a 29′ 18ga. vertical with a 31′ Jackite telescoping fiberglass pole. My unun is the classic T130-2 design mounted to a plastic winder. I also use a 16′ counterpoise and a 1:1 current balun at the feed point. I never fail to complete a QRP CW POTA activation with this antenna on 20, 30, and 40. It is my easiest one to deploy and it never lets me down. I found your site while researching optimum lengths, as I’d like to try 80 and maybe 160 in the future.

    Like

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s