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A Tropical Band Antenna with good Receiving characteristics

The EWE in the Garden


by Michael Schnitzer

The EWE antenna is fascinating. If you have it, you will ask yourself, why you didn't happen to think of that simple antenna form earlier. It is very effective for DXing on the tropical bands.

Since some time I tried to find an antenna, which first of all would have its maximum performance on the tropical bands. Secondly the antenna should be directive; thirdly the antenna should reduce the usual substantial noise level on the lower frequencies and should finally fit in a normal garden.

The past favorits, K9AY and Beverage, didn't come into consideration. The K9AY, by the way an advancement of the EWE, is a special MW antenna with moderate performance only on the tropical bands and the Beverage exceeds my property boundaries. The EWE antenna now fulfills very well all criteria specified above.

This type of antenna was described first in the year 1995 by the American radio amateur Floyd Koontz. He developed the EWE particularly for the application on 80m and 160m. In accordance with the specification of Koontz I copied the 80m version. By the way, "Ewe" is the English word for a female sheep (just an information to all non English native speakers), which is pronounced like the letter "U". Koontz obviously used a phonetic similarity as designation and alluded thereby to the form of the antenna.

Construction principle

EWE antenna structure

At first sight the antenna is nothing else as an inverted U of approx. 7,5 m length and with a height of three meters above the soil. These are dimensions, which fit in each average garden. One end is grounded over a resistor, the other end is attached over a core transformer (balun) to commercial coaxial cable RG 58.

The main direction of reception is the end with the balun and the coax connexion. The zero point is towards the terminating resistor. Depending on space conditions one can give preference to different structure versions. Thus e.g. length and height can be changed as well as the position of the feed-in, which can be attached likewise at the upper end of the vertical front element (bottom feed vs. top feed). You can find an illustration and other diagrams in the internet articles mentioned at the end.

Some antenna theory

The EWE resembles a simple vertical antenna system consisting of directive element and a grounded reflector, it's behavior however is completely different. The horizontal wire thereby acts as supply line between the two vertical parts and contributes insignificantly only to the reception. The excellent directivity of the antenna results from three combining phenomena:

1. Due to the different feed (feed element from down and reflector element from above) a phase shift of 180 degrees results between the two elements.
2. In the reflector the antenna current is approx. 65-70% lower than in the feed element. This fact alone however would cause only one foreward/back ratio of max. 8 dB.
3. At the same time the terminating resistor causes a decrease of the wave velocity in the reflector element. The higher the value of the terminating resistor is, the lower becomes the propagation speed in the reflector.

The combination of all three effects leads to the partial extinction of the signal arriving from the back and produces in this way a distinct rear zero point. One could say also, the EWE is "phasing" itself and causes therefore the excellent foreward/back ratio. Theoretically more than 35 dB can be achieved. According to the phenomena described above the EWE belongs to the category of the travelling wave antenna (e.g. the Beverage). In contrary to a simple vertical 2-element-antenna the EWE doesn't produce standing waves, which also explains the broad band behavior.

The terminating resistor

The value of the terminating resistor depends on several variables. The respective ground conductivity represents such an important variable. Bad ground conductivity means a smaller decrease of the wave velocity in the reflector. Therefore the value of the terminating resistor must be increased. Beyond that the resistor depends on whether the bottom feed or the top feed version is prefered. And modifications of the total dimensions of the system exert influence on the value of the terminating resistor, too. There always is to consider however that for each version the respective R-value is to be inferred either from relevant tables or from computer calculations or however must be determined experimentally.

In the last case a rear signal is tuned to maximum suppression with a suitable potentiometer. Concerning the structure version with 7.5 m length and 3 m height John Devoldere recomments the following data on 3.65 MHz: 1600 Ohms for bad conductivity, 975 Ohms with good ground conductivity and 700 Ohms for very good conductivity. If the EWE is bound for higher frequencies, the R-value should be decreased additionally.

According to my estimation an accurate r-value is very theoretical and cannot be fixed exactly. Practically only on medium wave one can find a clear notch in the signal strength of a rear station by the potentiometer approach. Thus I used a rear local medium wave station in order to determine the ideal value of the terminating resistor for max. signal suppression. This value amounts to 922 Ohms.

On short wave however this procedure is substantially more difficult. The signals are not so stable, and a clear R-value could not be found in such a way. In practice I could observe rather an interval of R-values. Within the range of 750 up to approximately 950 Ohms I could observe a rear signal suppression from 20 to 25 dB on my EWE version. Due to the fact that my EWE antennas first of all are bound for DXing on the tropical bands I determined the amount of the terminating resistor - half empirically, half theoretically and intuitively - on 820 Ohms.

Structure versions

Devoldere and Koontz describe several structure versions of the EWE. Hanging the horizontal wire on five meters height above the ground instead of three meters the antenna gain will increase 2-4 dB. Likewise the length can be changed. Further combinations result, if two EWEs are connected in parallel or in series, or if there is a cross-shaped arrangement in a quadripartite group with different switching possibilities.

East west combination

By chance I have in my garden three fruit trees exactly in a series, into the prefered DX directions east-west and accurately in the correct distance from each other. On that reason I decided to install two EWE antennas exactly one behind the other. Thus I have now an EWE towards South America (direction 260°) and an EWE towards Asia (direction 80°). I chose the bottom feed version, in order to can leed in the coax cable to the house exclusively in the earth. The length of the horizontal element amounts to 7,5 m and the height is three meters over the ground.

Feedpoint and balun

The antenna feedpoint impedance of the EWE varies between 300 and 700 Ohms. An impedance-matching transformer with turn ratio 3:1 (transformation 9:1) enables an adequate adjustment to the 50 Ohm coaxial cable.

Balun structure

Practical operation and reception results

The signal strengths: Meanwhile I often had the opportunity to compare the two EWEs to my remaining antennas, a 25m long wire and the DX One Professional. At the very beginning of this section I would like to warn all those, who are interested exclusively in strong deflections of the receiver's S-indicator. The signal strengths produced by the EWE basicly are below those of the other antenna types on all frequency ranges. Depending on the reception situation the observed signals are approx. 5-10 dB weaker. Only if the station is situated exactly in the main lobe of the EWE, the signal loss amounts 2-3 dB compared to long wire and DX-One. In practice however these data hardly are of relevant importance and aren't noticeable in average DX-operations. In more difficult cases I can connect a quite useful HF-amplifier, which additionally raises the signal around 7-8 dB and which so adjusts the "losses" compared to long wire and DX-One.

Another comparison should be of some interest. Using the neighbour's garden I temporarily established a 70m Beverage antenna with 1.20m height above the ground. This special kind of short-Beverage was directed to Indonesia, Australia and Papua New Guinea, which enabled the comparison of the Beverage to my Asia-EWE. All relevant tropical band frequencies of this region were tested. The EWE-Beverage comparison supplied a result quite surprising for me: Both regarding the signal strengths and regarding the noise level and the acoustic impression generally these two antenna types were completely identical! Thus the 70m Beverage wire produced no better results than a 7.5m EWE antenna. Who would have thought that?

The directivity

By the installation of two EWE antennas "radiating" in two opposite directions the F/B ratio can be demonstrated quite well. If a station is situated in the antenna main direction e.g. of the east-EWE and one switches then to the west-EWE, the signal strength decreases approx. 20-25 dB. With this arrangement however I could not achieve the value of max. 35 dB signal suppression as postulated in the antenna-theoretical discussions.

The following example may clarify, which practical effects the rear zero point can have. One evening I could receive RRI Jambi on 4925.2 kHz at around 22.15 UTC on the Asia-EWE. Switching over to the South America EWE I could listen to Radio San Miguel from Bolivia audible on same frequency without any interferences caused by RRI Jambi. Such a clear differentiation of two co-channel stations was not possible on the long wire and on the DX-One. Something similar was to observe concerning the Peruvian station Radio Libertad from Junín on 5039.2 kHz. In the late evening there are sometimes disturbances by a Chinese station on 5040 kHz, which can be suppressed almost completely by the application of the LA-EWE.

My domestic satellite TV set so far made absolutely impossible DX on 90m and 120m. Long wire as well as DX-One cannot eliminate the electric noise level. Using the Asia-EWE I succeeded for the first time to listen to ABC Alice Springs on 2310 kHz, despite of TV consuming family.

Concerning medium wave DX the two opposite EWEs are a real enrichment. It makes fun to check the entire medium wave scale in the evening hours shifting up and down the two EWE-antennas on certain frequencies. The Asia-EWE opens a great part of the Middle East. Numerous Arab speaking stations become audible, which otherwise perish completely in the overcrowded European MW-powerband. Some examples of the later afternoon and early evening in October and November 2000:

198 kHz: BBC on the west-EWE; using the east-EWE PR 1 Raszyn came through.

738 kHz: RNE Barcelona on the west-EWE, Kol Israel with Arab program on the east-EWE.

1017 kHz: The local SWR as expected on the west-EWE. The east-EWE suppressed completely the SWR and a Turkish station became audible.

1053 kHz: On 80° Romania came in quite well, on 260° a UK station. Separation almost completely.

1413 kHz: BBC Oman on the east-EWE with O=4-5. Long wire and DX One produced noise here only.

1458 kHz: Here one could choose between Radio Tirana and Sunrise Radio by switching the two EWE-antennas.

Frequency range

Contrary to "standing wave antennas" (e.g. dipoles) the EWE enables broad-band reception. The directivity is provable from approx. 150 kHz up to approximately 10 MHz. The EWE therefore can be used without any problems from long-wave band up to the 31m-band. One evening I could observe six Brazilian stations on 31m using the LA-EWE between 21.30 and 22.00 UTC.

The signal level thereby was about 5 dB lower compared to the long wire. The directivity of the system could be demonstrated quite clearly. After switching to the Asia-EWE practically nothing more was to be heard from the Brazilians. Above 10 MHz the signal strengths substantially decrease in comparison to the long wire, and a rear zero point cannot be found any more.

Noise level and other disturbances

The actual highlight of the EWE antenna is the quietude of the signal! As we all know, the main problem of low band DXing is noise on the relevant bands. In particular long wire antennas pick up each electrical disturbance from ionosphere and atmosphere (thunderstorms etc.), or caused by the neighbourhood (computer, TV set etc.). Using the EWE for the first time the DXer learns an absolutely striking new experience: He often can enjoy a clearer and fewer disturbed signal.

Regarding the entire audio impression and cleanness of reception the EWE is unbeatable in many cases. In particular the long wire is beaten concerning this criterion. The EWE does not only reduce a part of the electrical noises, but beyond that it also suppresses all those reception impairments, which are due to rear stations. Annoying interference whistling can disappear only by switching from long wire to EWE, or disturbances caused by a European power station on the adjacent channel are reduced.

Construction tips

Basically no other regularities apply to the construction of an EWE as to other antennas, too. Proximity to metallic articles such as gutters, gutter-pipes etc. has to be avoided. Beyond that the location of the antenna should be far away from the house, as far as the garden size permits.

Balun and terminating resistor can be accommodated comfortably and weather-proofed in small current distribution boxes, which are available in each market for household goods. These boxes can be fastened easily to the ground rods.

Summary

The EWE will not and cannot solve each reception problem. It doesn't replace other antenna forms under any circumstances. Who exclusively prefers listening to international radio stations certainly can use the classical long wire or a magnetic antenna without any problems.

The DXer however usually is hunting local radio stations, far away and with poor transmitting power only. And all these African, Indonesian or South American stations, which are to be found normally on the tropical bands of 60m and 90m, often disappear in the noise of electrical disturbances. Here the EWE can be a certain remedy indeed. If one has several antennas, then one chooses the best one in each case anyway. Concerning all stations coming in from the correct direction, there can be said: The EWE-antenna almost always produces the calmest signal!

Erection and assembling are remarkably simply. All needed structural parts are available for a few money only. The dimensions of the EWE enable the mounting in each average garden. I also can recomment the relevant literature to this topic. It supplies an additional view on the theory of the EWE and on its function principles and gives suggestions for further structure versions. Finally I would like to thank the DXers Thomas Adam and Thomas Berner, who advised me concerning the antenna-theoretical reflections.

Sources:
John Devoldere, ON4UN: "Low-Band DXing", USA, 1999
Floyd Koontz, WA2WVL: "Is this EWE for You?", QST Volume 79, 1995

The article of F. Koontz in the Internet (for ARRL members only):
http://www.arrl.org/tis/info/pdf/9502031.pdf
http://www.arrl.org/tis/info/pdf/9601032.pdf

Would you like to comment on the article or ask a question? You can continue discussion on the article and EWE antennas at the DXing.info Community Forum for antennas.

Written in November 2000, published on DXing.info on May 15th 2002

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