Monthly Archives: October 2017

JOTA 2017

JOTA/JOTI (Jamboree on the Air/Jamboree on the Internet) celebrates the scouting movement on the air and on the internet. This years event happens Oct 20-22. On Saturday October 21, a few of the members of EARS will be attending the event with the Sparta Scouts and Venturers at the Sparta Community Hall and setting up amateur radio stations and attempting to contact other groups with similar setups.

Come on out between 12 and 4 and meet other scouting members and talk to other groups via radio.



More info: QRP-Labs QCX | QCX build video | QCX review video

End Fed Antennas

EARCHI End Fed Matchbox

An end fed antenna consists of a wire fed on its end, the length of that wire is not resonant with any frequency or frequencies you will be using it on. Lengths of a half-wave or multiple must be avoided. The transformer usually used with an end fed wire is a 9:1 transformer. This transformer converts the impedance at the end of the random wire down to about 50 ohms, a value which any modern transmitter can transfer power to and has been designed for.

Notes from W1SFR:
In the case of the end fed random wire, some lengths are better than others because of the harmonic effect of the length of the wire and how that affects the various band on which you wish to operate. Counter to tuning a length of wire like you would with a dipole, with a random wire you don’t want the length to be harmonic on any band. There are ideal lengths that have been mathematically determined to be best for randon wires. Here they are:

29 35 41 58 71 84 107 119 148 203 347 407 423

I have chosen 35′ as the standard length for my antennas, but you can experiment. I have used up to 84′ and the KX3 will still tune all bands but as the wire gets longer so does the resistance so it becomes harder and harder for the tuner to do its job. At 35′ it’s not too short and not too long and works great in every configuration I’ve tried so far.

9:1 unun transformer:

my 9:1 unun using a T130-2 toroid:

End Fed Half Wave Antennas

Facebook Group – EFHW Antennas

Steve Ellington N4LQ started up a group on Facebook called End Fed Half Wave Antennas. The purpose of this group is to explore the use of an end fed half wave antenna. An end fed half wave antenna is one of a specific length depending on the frequency that it is to be used on, for example, an end fed half wave antenna for 80 meters is about 130′ long. The length of a half wave antenna is calculated using the following formula: L (ft) = 468 / f (freq in mhz). The end fed half wave antenna presents a large impedance to your rig, so this impedance must be stepped down to a more useful impedance that is closer to 50 ohms. Most radios today expect to see an antenna with an impedance of 50 ohms at the end of it.

End-fed Half Wave antennas (or EFHWs) cover multiple bands without traps, stubs, or resonators. End-fed wires resonate on their 1/2-wave fundamental frequency plus all odd and even harmonics above. By adding a broad-band matching network, the wire’s high impedance feed point is transformed down to 50 ohms across a wide frequency range and, in most cases, you don’t need a tuner to operate. Note that a single-wire radiator may be installed using only one high center or end support, making it fast and easy to set up at home, on the road, or as a “grab-and-go” emergency antenna.

There are many different ways to transform this impedance to 50 ohms. The one that Steve promotes is to use a 49:1 unun and information about this method follows.

The following is a diagram which explains how to construct a 49:1 transformer.

Wound with #14 enameled wire using FT240-43 toroids:

Steve made a video in which he showed the results of antenna tests using various setups.
Video: EFHW Installation Summary or Is your feed line part of the antenna?

Steve’s best test results were with the transformer grounded close to the ground and fed with enough coax to reach the transmitter also grounded. Details are shown in the next two images:

Steve Ellington’s antenna:
133 ft. inverted L with 51 feet vertical. Transformer grounded, very well. Coax on ground 100+ feet to shack, no chokes. Home brew transformer 2 primary 13 sec. mix 52 three stacked cores. 14 ga wire .. swr acceptable …below 2.5 and much lower

Modification for 75 meters:
Here is how to raise the resonant frequency on your myAntennas EFHW-8010 for 75 meter phone operation without affecting the other bands. Simply cut the antenna at the half way point and insert a capacitor. 500pf will put you at around 3700khz. Lower values i.e. 300pf will raise it even higher. I suggest a ceramic disc capacitor rated for at least several KV just to be safe. I have tested and verified this and it works great.

Videos by Steve Ellington N4LQ related to EFHW Antennas:

myAntennas EFHW-8010-1K

49:1 Transformer Vendors