The U01 Emergency communications Antenna – NVIS linked EFHW for 80/60/40/20/17/15/10m

Pocket EFHW (40/20/15/10m EFHW)

Linked Dipole for 80/60/40/30/20m

At this Point in time, my „Antennas“ Page is mainly circeling around the Endfed-Halfwave. It is easy to build and once you have understood the principle, you will realize it´s always the same pattern, regardless of your execution.

The EFHW has some unique properties, that are really interesting for portable use:

  • Easy to build (Only Transformer + Wire)
  • Easy to elevate
  • Easy to feed from the end
  • Resonant on fundamental and all harmonics !!!
  • So it is by nature a Multiband Antenna

Disadvantage is: We´re losing between 15-25% of Energy in the Broadband Transformer.


Everyting starts with a Broadband Transfomer with Impedance Transformation ratio of 1:49. In my case, the Transformers are ALWAYS wound on -43 Material.

See this Video for detailled explaination of theory and winding pattern:

The Winding Pattern is determined by Core Size, and the Core Size is determined by the maximum Power, you are planning to run over the Antenna:

Core SizeWinding Ratioavailable PCBsMax Power CW / SSBMax Power FT8
FT140-432T:14TU01 HASP100W50W

As visible in the Table above, there are several PCB´s that help you in various ways.

Here´s a short Video on how to use the provided Files to order some PCBs

The smaller ones (DG1JAN / DL2MAN) at least provide a space for the Transformer to mount, the compensation capacitor, the Antenna connector and have mounting holes to attach Antenna wire and tensioning rope.
The more advanced ones (DL2MAN HASP / U01) even provide hasp functionality, so you can wind your antenna wire and rope on it. For those advanced PCBs, there are also covers to 3D Print available (FT114 / FT140) , so Transformer and Capacitor can be weather proofed. So everything is one compact package and ready for transport or setup.

Antenna Wire

Depending on what you want to use your Antenna for, you simply add the needed amount of wire to the Transformer and you have an Endfed Half Wave.

You can use almost anything, that conducts electricity

  • magnet wire (light, almost invisible, but not very durable)
  • loudspeaker cable (cheap, everyone has some amount lying around but it stretches under load)
  • Antenna wire (more expensive, but very durable)

For most of my portable Antennas I went over to using DX-Wire UL, as this is very lightweight (4g/meter), small (1,6mm Diameter), very flexible and has very high tensile strength (60kg of pull force before break). It has internal Kevlar Fibre, that creates its unique properties.

For most of my stationary Antennas I´m using DX-Wire FL. It´s a little bigger and heavier, but has no twisted wires inside, so it does not lengthen under load. It has better conductivity, more cross section and is made from hardened copper. All DX-Wire products are UV resistant and will last forever.

By the way: I´m not getting paid or discount from DX Wire. I´m a regular customer. It´s just, that I appreciate good material and I´m recommending, what I´m convienced of. Using good material will save you some frustration.

Wire Lengths

By adding a wire with the length of 1/2 Lambda to the Transformer, the story could be over. Basically that´s it, but wait, theres more 😉

In practice, the required wire length depends on elevation height. In theory the Impedance of an endfed half wave should be infiniately high (at feeding point and endpoint), as it´s the end of the wire, and no current should flow past the end of a wire. In practice, we get away with transforming our Impedance to 2450 Ohms (+/-) at the feeding point. Did you ever ask yourself whay that is ?

The answer is simple: There is current flowing, otherwise we could not transfer energy into the Antenna, and the Impedance as well as the amount of current flowing, is dependent of the elevation above ground. The Antenna interacts with the Ground, which is a capacitive effect. There are more clever and skilled people, that you can ask about the physical and electrical details. I will try to limit my advise to practical values. Rule of thumb: The lower the Antenna, the lower the feeding impedance. The higher the Antenna, the higher the feeding impedance.

This has also influence on the wire length, that makes the Antenna resonant on your desired frequency.

Starting Point is:

λ = c/f (Wavelength = Speed of Light / Frequency)

For ease of use: Lambda (in m) = 300 / Frequency in MHz

Half of that length is our Antenna wire length. If you start with that, you´ll always have enough wire to shorten it until it is resonant.

The following table shows wire lengths, that were found to work, when using the Antenna in elevation heights between 1m above ground up to 8m above ground (regardless of elevation pattern) Probably that´s the range we will be facing in any portable setup / use:

FundamentalResonator LengthAdditional Length (Feeding / Insulator Loop)Total Wire Length (Cutting Length)Covered Bands
80m39,2m0,15m Feeding +0,1m Insulator39,45m80/40/20/15/10m
60m26,4m0,15m Feeding +0,1m Insulator26,65m60m/(30m)
40m19,77m0,15m Feeding +0,1m Insulator20,02m40/20/15/10m
Wire Lengths for Lower elevation heights, as common for portable use

Addional Requirements

Use at least 0,05 Lambda length of coax cable to feed it !

For 80m Band, this would be 4m of coax cable, so we recommend to use at least 5m of coax cable to feed any EFHW. This not only acts as counterpoise. When lying the feeding line on the ground, the coax cable also reduces common mode currents.

Special Variants

DJ5REs U01 Antenna – A linked EFHW for NVIS use, that covers more bands by „connecting“ or „disconnecting“ wire length.

Support Material

This is a collection of 3D Print Files, that help you, building any EFHW:

3D Printable HASP. You can scale it up or down, to fit your personal needs. I´ve used it at 130% for the Pocket EFHW. I´ve used it at 100% to organize the guy lines of my Poles. Credits to oxyge65 for designing and sharing.

Center Triangle + Rope Tensioner for 1mm Rope / Thin wire

Center Insulator and Rope Tensioners for 2mm Rope and UL Wire (recommended)

Transformer Cover for U01 Hasp PCB

Transformer Cover for (small) DL2MAN Hasp PCB

Stuff for the Poles I´m using:

DX-Wire Mini (10m) – Top 4 Elements removed:

DX Wire Mini Guy line mount

DX Wire Mini Tip to attach Antenna

Spider Beams Mini 10m – Top 4 Elements removed:

Spiderbeams Mini Guy line mount

Spiderbeams Mini Tip to attach Antenna

If you find that information helpful, I´d appreciate if you donate me a coffee or beer: