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.
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.
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 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
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.
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 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.
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?
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
1413 kHz: BBC Oman on the east-EWE
with O=4-5. Long wire and DX One produced noise
1458 kHz: Here one could choose
between Radio Tirana and Sunrise Radio by switching
the two EWE-antennas.
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
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.
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
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.
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
John Devoldere, ON4UN: "Low-Band DXing",
Floyd Koontz, WA2WVL: "Is this EWE for You?",
QST Volume 79, 1995
The article of F. Koontz in the
Internet (for ARRL members only):
|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
Written in November
2000, published on DXing.info on May 15th 2002