The measurements below are for building a Double Extended Zepp . The wire size can range from 16 AWG to 12 AWG . The lower the wire number the wider the bandwidth . For example 12AWG will have a lower swr ( Standing Wave Ratio ) over a greater frequency range than 16 AWG .
The measurments below are in feet and inches . I have rounded off some of the measurments so it will be easier to measure them .
You should install a 4:1 current balun on the end of the 450 ohm latter line stub and the balun needs to be at least twice the operating wattage to prevent the balun from burning up from the swr mismatch on frequencies other than what the antenna was designed for . Don’t be cheap , you will not save money if you have to keep replacing the balun .
Remember the longer the antenna is the lower in the band it will operate , you can tune a long antenna with an antenna runer but you cannot tune a short antenna . Best suggestion is to make the antenna for the lowest operating frequency so that you can operate the entire band you desire .
| Operating Frequency |
Double Extended Zepp 1/2 Antenna Length A= This measurement |
450 Ohm Latter Line Stub Length B=This measurement |
| 1.8 Mhz. | 333′ 4′ | 57′ 2 5/8″ |
| 1.9 Mhz. | 315′ 9 1/2″ | 54′ 2 1/2″ |
| 2 Mhz. | 300′ | 51′ 6″ |
| 3.5 Mhz. | 171′ 5 1/4″ | 29′ 5 1/4″ |
| 3.6 Mhz. | 166′ 8″ | 28′ 7 3/8″ |
| 3.7 Mhz. | 162′ 2″ | 27′ 10″ |
| 3.8 Mhz. | 157′ 10 3/4″ | 27′ 1 1/4″ |
| 3.9 Mhz. | 153′ 10 1/4″ | 26′ 9″ |
| 4 Mhz. | 150′ | 25′ 9″ |
| 5.4 Mhz. | 111′ 1 3/8″ | 19′ 7/8″ |
| 7 Mhz. | 85′ 8 1/2″ | 14′ 8 1/2″ |
| 7.1 Mhz. | 84′ 6″ | 14′ 6″ |
| 7.2 Mhz. | 83′ 4″ | 14′ 3 5/8″ |
| 7.3 Mhz. | 82′ 2 1/4″ | 14′ 1 3/8″ |
| 10.1 Mhz. | 59′ 4 7/8″ | 10′ 2 3/8″ |
| 10.15 Mhz. | 59′ 1 3/8″ | 10′ 1 3/4″ |
| 14 Mhz. | 42′ 10 1/4″ | 7′ 4 1/4″ |
| 14.1 Mhz. | 42′ 6 5/8″ | 7′ 3 5/8″ |
| 14.2 Mhz. | 42′ 3″ | 7′ 3″ |
| 14.3 Mhz. | 41′ 11 1/2″ | 7′ 2 3/8″ |
| 18.068 Mhz. | 33′ 2 1/2″ | 5′ 8 3/8″ |
| 18.130 Mhz. | 33′ 1 1/8″ | 5′ 7 1/8″ |
| 21 Mhz. | 28′ 6 7/8″ | 4′ 10 7/8″ |
| 21.1 Mhz. | 28′ 5 1/4″ | 4′ 10 1/2″ |
| 21.2 Mhz. | 28′ 3 5/8″ | 4′ 10 1/4″ |
| 21.3 Mhz. | 28′ 2″ | 4′ 10″ |
| 24.890 Mhz. | 24′ 1 1/4″ | 4′ 1 5/8″ |
| 24.950 Mhz. | 24′ 1/2″ | 4′ 1 1/2″ |
| 28 Mhz. | 21′ 5 1/8″ | 3′ 8 1/8″ |
| 28.5 Mhz. | 21′ 5/8″ | 3′ 7 3/8″ |
| 29 Mhz. | 20′ 8 1/4″ | 3′ 6 5/8″ |
| 29.5 Mhz. | 20′ 4″ | 3′ 5 7/8″ |
Article by N8ITF originally available at http://home.comcast.net/~n8itf/doubzepp.htm
Hello Simone,
I hope this finds you well.
I came across your nice article, “Building a Double Extended Zepp Antenna”.(http://www.iw5edi.com/technical-articles/building-a-double-extended-zepp-antenna)
You provide a table with recommended antenna length and 450 Ohm ladder line length. For example for 14.2 MHz each leg should be 42? 3? and the ladder line stub 7? 3? (12.8m and 2.13m).
Will these lengths make the antenna resonant (SWR 1:1) on this particular frequency?
Using your recommended lengths for 14.2 MHz and a 4:1 balun, I got 2.5 SWR at 15.8 MHz.
Should it have been SWR 1:1at 14,2 MHz? Do we achieve 1:1 resonance with your recommended measurements at the desired frequency or how else can I check my antenna works as you intended by the lengths you recommend? Any pointers perhaps please?
Many thanks
Tim