W3EDP End Fed Antenna

The W3EDP antenna is a form of end fed wire antenna used for the HF bands that was first described in 1936 by H. J. Siegel, W3EDP .

Long Wire / End Fed Wire Antenna Includes:
End fed / long wire antenna Multiple wavelength long wire End fed half wave antenna W3EDP antenna Random wire antenna

The W3EDP antenna has been available for very many years: the first description of it appeared in the ARRL publication QST March 1936 in the Experimenter section under the title "An Unorthodox Antenna." It was written by Yardley Beers, W3AWH about the experiments that his friend H J Seigel W3EDP had undertaken.

The W3EDP antenna is a development of the early Zeppelin or Zepp antennas that were used before the Second World War. They obtained their name from the fact that end fed wires were required for use on Zeppelin airships.

Today, the W3EDP antenna is still widely used - it is ideal where a straightforward end fed wire is needed for HF multiband ham radio operation.

Obviously the performance depends greatly upon aspects such as the height of the antenna, the location, etc, but overall the users of the W3EDP antenna have confirmed that it operates well, and it is particularly well suited for portable operation because it is very easy to quickly erect.

W3EDP antenna basics

As the understanding of antenna operation was as well understood in 1936 as it is now with software like EZNEC, etc, the W3EDP antenna was designed by trial and error.

W3EDP took a long length of wire, tabulating results and progressively cutting lengths off until the best performance as obtained. A similar process was undertaken for the counterpoise.

The antenna was deigned for the ham radio bands of the day: 160, 80, 40, 20 and 10 metres.

Details for the W3EDP antenna are quite straightforward, and it is basically another version of an end fed wire antenna.

The antenna is fed via coaxial cable and passes through a tuned matching transformer. It was stated in the original QST that a low value of capacitance int he antenna circuit gave by far the best efficiency.

The radiating elements consist of a 84 foot (25.6 metres) and this is fed against a 17 foot (5.2 metre) counterpoise.

Although the 84 foot radiating element remained the same for all bands, W3EDP found that although the 17 foot counterpoise worked well on most bands, on 20 metres, a length of 6 ½ feet "seemed to outshine all the others."

The W3EDP antenna is particularly useful when the station is in a room above ground. Other antennas like a simple end fed wire often called a long wire antenna would need a good earth connection for the antenna to operate correctly. The counterpoise for this antenna enables it to operate effectively without the need for a good ground connected via a short lead.

The original W3EDP antenna was directly coupled to the transmitter tank coil. The counterpoise was connected to the end of the coupling coil nearest the tank coil as shown.

Original set up of the W3EDP end fed antenna — Original set-up for the W3EDP end fed antenna

The topology of the early valve / tube amplifiers required the correct loading of the circuit to obtain the required output. Often the coupling between the two coils was arranged to variable to enable the operating conditions of the valve to be set for the correct loading and hence output power.

Matching / feeding W3EDP today

Today, the way in which final amplifiers are designed requires that a good impedance match is seen by the final amplifier in the transmitter or transceiver. This is often achieved by ensuring that the correct impedance match is provided by the transformer at the base of the radiating element. This normally includes a tuning capacitor as in the original diagrams for the antenna.

It is also possible to feed the antenna using an unun (and RF transformer that transforms the impedance and is unbalanced on the input and output - hence the name unun rather than the more familiar balun which converts from balanced to unbalanced.

Commercially made 4:1 and 9:1 versions are available and these could be used.

When using this antenna, it is most likely that an antenna tuner close to the transmitter will be needed to ensure that the level of SWR seen by the transmitter is sufficiently low, otherwise the PA protection circuits may see a high SWR and reduce the output power.

Results

The results achieved by H J Seigel, W3EDP in his development of the antenna before 1936 were impressive.

Quoting the original article the writer states:

Though this antenna may seem unorthodox to many, the results obtained with it should justify it fully. Using a pair of 46's [vacuum tubes / valves of the day] and 50 watts input to the final PA [this would mean around 33 watts output] W3EDP has consistently received R7-8 [S7 to 8 in today's parlance] on 7 and 14 mc from five continents. He has worked 75 countries in all continents with this little rig from an average DX location, a record not duplicated by many using higher power . . . .

Today many people have used the antenna with good results and have found it a reliable and easy to install antenna.

In the final paragraph of the "Unorthodox Antenna" piece within the Experimenter section of QST describing the W3EDP antenna, the writer says:

This antenna is not offered to the reader as a cure-all for his antenna troubles. To discover its true value it will have to be tested at more locations of different characteristics. The dimensions may have to be altered slightly in some locations for maximum efficiency. It is the writer's belief that the design of this antenna perhaps may be the basis of further antenna experiments.

Despite the initial concern over the operation of the antenna, it has been in use, and proved to work well as an easy to construct and install antenna. It has remained virtually unchanged since it was first publicised all those years ago in QST, and is a very popular form of antenna for many ham radio operators, especially those who are operating portable, for example those who operate for the Summits on the Air, SOTA operating.