Rockwell wrote a 4-part series on station design for long distance
(DX) communications that covered antenna selection and siting
I), economics and construction(Part
II), station configuration and receiver topics
III), and propagation quirks and operating tips
IV). This first part goes into some of the gory detail
of surrounding terrain considerations and necessary antenna launch
angles, complete with equations. Most of the work is based on multi-element
horizontal Yagi antennas. The term "forezone," of which a formal
definition is not locatable in a Google search (no reference to
it at all), is used throughout the series, and refers to the radiation
area in the forward direction.
September 1966 QST
Wax nostalgic about and learn from the history of early electronics. See articles
QST, published December 1915 - present. All copyrights hereby acknowledged.
Station Design for DX - Part I
Part I - Antenna Topics and Siting
BY Paul D. Rockwell,
Most of what has been written on the subject of optimum station
design for DX has been on one aspect at a time. This article assembles
various aspects, in the system-approach sense, and is specifically
addressed to optimum design for c.w. DX. However, most of the ideas
apply also to 'phone operation. Antennas and propagation will be
discussed in respects believed to be not generally appreciated.
Most of the topics are already familiar to top DXers, but one or
more should be useful or interesting to nearly any serious DX operator.
Antenna at K2HLB.
The writer expresses his appreciation for many helpful comments
and suggestions in voluminous correspondence with top DXers. It
was heart-warming to receive so much cheerful encouragement, advice
and many contributions. Only one sharp criticism was received: that
DX is 90% operator, 10% equipment. Maybe so - but look at Table
1. The successful DX-contest performers who bring up this point
usually have several of the following: (a) a full gallon; (b) a
tower over 65-feet high; (c) a boom over 30-feet long; (d) a quiet
location; (e) a hilltop site.
Firstly, horizontal is by far the preferable polarization.
The problem with vertical polarization is primarily with ground
losses. Broadcast stations customarily use 120 buried radials to
overcome these losses. Such an installation is impractical for amateurs.
Radiation efficiency is probably les than 20% for an installation
employing say, four radials. G.H. Brown, in PIRE, June, 1937 says
that for quarter-wave antennas with 0.4λ radials, efficiencies
the vertical radiation pattern is characterized in practical locations
by a null at the low angles. The low-angle radiation of a ground-mounted
vertical quarter-wave, often shown for perfect earth as being good
right down to 0° elevation, actually has a null there.
1,2. Vertically polarized antennas are more susceptible to
QRNN (man-made electrical noise) than horizontally polarized.
With horizontal polarization, the antenna is balanced with
respect to ground, and ground losses are customarily only a few
percent. Under certain circumstances, a vertical ground-plane can
be advantageous, i.e. (a) for a saltwater reflection-zone, (b) for
its set-up convenience on DXpeditions,3 or (c) for constructional
and economic advantages on bands lower in frequency than 14 Mc.4
Even in such cases, the vertical loses important advantages of (1)
gain, receive and transmit, and (2) receiving effective S/N, including
rejection of QRM from undesired directions.
which deserves mention is the question of gain quotations on Yagi
antennas. Manufacturers have stated these gains in ways which may
be confusing. One manufacturer, for example, chooses to relate the
gain of a horizontally-polarized antenna-array at optimum height
above ground, to a half-wave dipole in free space. In this way he
gives himself 6 db of ground-reflection gain. His quotation should
be correspondingly discounted. The practical basis of comparison
is to a half-wave dipole, same height and foreground. Almost all
manufacturers, when they do not state that the gain is related to
a half-wave dipole, are relating their gains to an isotropic radiator.
This raises the gain by 2.2 db as compared to gain over a half-wave
dipole. If the manufacturer has assumed that the reference isotropic
radiator is in free space, whereas his array is at optimum height
above a perfectly reflecting ground, then his quotation should be
discounted by 8.2 db.
The most helpful relation in evaluating
gain in a Yagi antenna is the formula:
where L is length of the boom in the same units as the operating
wavelength, λ. Here the gain is that of the Yagi over a half-wave
dipole, broadside, at the same height and foreground, expressed
as a factor.5,6. In db,
This rule is good for optimized designs with element spacings
up to approximately 0.2λ maximum. It says some designs are
carrying more elements than they need, and may be delivering less-than-optimum
performance on that account.
The rule becomes less accurate as the boom length goes below a half
wavelength. Fig. 1 is a useful guide. It is taken, and somewhat
shaded, from another reference.6
Fig. 1 - Boom Length (λ) vs. Gain (dB)
For quads, use
Fig. 1 plus 2 db, but only at the quad's optimum-design boom-length.
The quad may be considered, for estimating gain patterns, as two
vertically-stacked Yagis, The vertical spacing, however, is less
than optimum: so 2 db. is a better approximation than the 3 db which
would apply in principle for phased arrays. Quad power-gain does
not increase linearly with boom length, as is substantially the
case with Yagis. Also, quads are more susceptible to side lobes
of polarization orthogonal to that of the antenna's nominal polarization.
Since h.f. signals arrive with random polarization, this means side
responses may be expected to be, relative to Yagis, a problem.7
Measurements of antenna gain are tricky. Usual complications
are (a) ground reflections, (b) impedance matching, (c) near-field
effects, (d) reflections and absorptions from nearby objects, (e)
calibration of measuring detector and attenuators, and (f) polarization
effects. When scaling is attempted, further complications are incurred.
The subject is treated professionally.8 The same material
is published as IEEE Standards No. 149 (Revision of 48 IRE 2S2).
January, 1965, and is available from IEEE Headquarters, 345 East
47 Street, New York, N. Y. 10017.
has worked 310 countries on 20 c.w. only, in the period 1962-1965,
from a topographical depression beside a 4-lane highway in the middle
of greater Washington, D.C. Looking levelly from. the peak of his
roof, he sees neighbors' basement windows on all sides. This is
not a construction article. Rather, this series will present some
new and stimulating ideas on subjects such as antennas, station
apparatus configuration, most useful apportionment of dollar expenditures
on various station components; etc.
From the foregoing,
one might infer that Yagis and quads are all a ham should use. Because
they can be rotated, this is not far from correct for 10 through
40 meters, where most DX is worked. Log-periodics are unattractive
for hamming because of their low gain, high cost, and structural
complications. For really high gain, up to, say 16 db., a rhombic
can be a good dollar's worth, real-estate considerations permitting.
Rhombics call be nested - that is, several can be stacked, with
azimuths in various directions, on the same tract. Inter-couplings
are less than commonly supposed.9 Sloping Vs are of course
The matter of good siting has been appreciated
by amateurs for many years. Recent work11 has made the
criteria more clear. For the long hauls, the higher the antenna,
the better. Try for a radiation angle ("take-off" angle) main lobe
at 1° elevation. It is especially effective to locate an antenna
of modest height on a cone-shaped hill on which the ground slopes
downward in all directions for a thousand feet or so at an angle
of, say, 20°. If you have such a fortunate fore zone, 50 feet
is a good height for your 20-meter antenna.
for angle of maximum radiation (horizontal antennas, flat terrain)
where h is height (in same units as for wavelength, λ)
of the antenna relative to the ground-reflection zone in the foreground.
Required height for a given take-off angle is
For 1° at 20 meters, flat terrain, this is about 1000 feet!12
Hence, just figure the higher the better.
(Fresnel) zone extends as an approximately elliptical area on the
antenna forezone. The geometric ground-reflection point in this
zone is at a distance
from the antenna.
For 1° take-off angle, flat terrain,
at 20 meters, this is about ten miles.
The near-end distance
of the ground-reflection elliptical area13 is given by
and the far edge by
or about 1.7 and 58 miles, respectively, for 1° take-off.
Ground reflections have been the subject of published material complete
Fig.2 - Terrain Profiles
Profile Toward Australia (W.) from W6AM
(The ray tangent
is at 51 Miles. Effective height: 1290 feet.)
Table I - Antennas at DX Contest-Oriented Stations (20 meters)
A consideration for sloping
sites, in addition to the marked reduction of optimum antenna height
as mentioned above, is the reduction in size of the ground-reflection
area. For a 20° sloping forezone, the reflection area is about
the size required for 20° take-off angle on flat terrain, or
a maximum far edge of about 1/6 mile.
losses at h.f. for the grazing angles of interest, say 10° take-off
angle, are almost never serious for horizontal polarization and
are of the order of a few percent. Ideas of h.f.-site impairment
by magnetic masses, etc., under the ground surface are superstitions.
Some conspicuous examples of well-sited stations are W3CRA,
W4KFC, and W6AM. These stations have (in some directions) radio
horizons at distances of 20-50 miles. Radio profiles are presented
in Figure 2. Vertical angles are not significant on charts like
The advantage of a good site and/or a high antenna
can be of the order of 10-20 db11 compared with modest
suburban-neighborhood installations. It leads to situations where
the" mortals down below" can't even hear traces of the other end
of comfortably solid DX QSOs being conducted from the best sites.
Incidentally, in progressive antenna changes at W3AFM, increments
of only 2 db. in antenna gain have opened up, in each case, a new
layer of workable central-Asian DX.
Examples of high antennas
with long-boom Yagis, terrain essentially flat, are W5VA, W3MSK
and W3PZW. They, too, conduct what seem to be one-sided DX QSOs.
AA quiet location can make a telling difference. W2FZY,
who seems to hear everything with a modest antenna, attributes his
success largely to quietness of site. Some of the new appliances,
notably mixers and bed heater-pads, can ruin DX reception in ordinary
urban areas. Where there are only one or two such nuisances, they
can be tracked down by auto and portable transistor radios. Their
direction can be determined, within about 30°, by beam swinging.
Once located, the problem can be corrected by (a) buying a new appliance
and trading it for the offending one (b) offering an LC filter (such
as Lafayette 99R4005), (c) both the above. W3AFM's worst offenders
have been found within 400 feet. Lesser offenders have been located
and corrected at distances up to 800 feet.
Trees and foliage
are less of a problem in h.f. communications than generally imagined.
The attenuation varies from a small fraction of a db. for horizontal
polarization to 3 db. for vertical polarization. The values apply
to 30 Mc through moderately-thick trees as encountered in temperate
zones. Attenuation through a brick wall is 2 to 5 db at 30 Mc.15,16
For plotting profiles of your site, excellent contour maps,
7 1/2' X 7 1/2', (i.e. 7 1/2 minutes of latitude by 7 1/2 minutes
of longitude) may be had for almost any part of the U. S. A. at
30¢ each. Detail is such that individual houses may often be identified.
For explicit ordering information contact: Map Information Service,
Geological Survey, Washington, D. C. 20242. (Part II of this series
will appear in an early issue.)
1 Jordan, "Electromagnetic
Waves and Radiating Systems," Prentice-Hall, 1950.
2 Anderson, "Antenna Behavior over Real Earth," QST June,
3 With respect to DXpeditioning Gus (W4BPD)
has found it satisfactory to put a 14 AVQ atop the tallest pole
he can find, often 40-50 feet. He uses 4 guys. Two of these are
insulated at 40 meter quarter-wave points, the other two at 20-meter
quarter-wave points. A hole is dug, guy anchors set, and the antenna/pole
"walked" up with the aid of pike poles.
W3BMX, "At W5KZA I had a pair of phased ground-planes on 7 Mc.,
quarter-wave spacing and 90° phasing which could be reversed,
flipping the cardioid pattern 180°. Each GP was 20 feet above ground
at the base and had 12 radials. Front-to-back ratio was consistently
20 db. on the nose and the gain about 3 db. Many fellows thought
I was kidding when I worked JAs, VS1s, VS6s. DUs, etc., at 9-10
A.M. during the winter months. I was quite impressed with the antenna.
It does pick up noise, however; so in a noisy QTH it would not be
worthwhile. Its broad radiation characteristics and flat s.w.r,
(within 1.5:1) over entire 7-Mc. band were useful and nice to operate,"
5 Simon and Biggi." Un Nouveau Type d'Arien,"
L'Onde Electrique, Nov., 19:54.
Ehrenspeck and Poehler, "Maximum Gain from
Yagi Antennas," IRE PGAP, Oct., 1959.
Quad Antennas, Radio Publications, Wilton , Conn. 1959.
8 "IEEE Test Procedures for Antennas," IEEE Transactions
on Antennas and Propagation, Vol. AP-13, No.3, May 1965, pp. 437-466.
9 Viezbicke, Interactions
between Nested Rhombic Antennas," NBS Report 6773, Sept. 12, 1961.
10 King, "Performance of an Inclined Vee Aerial,"
PIRE, Australia, Sept. 1963.
Utlaut, "Effect of Radiation Angles on HF
Radio Signals," Radio Propagation NBS CRPL-D, Mar./Apr., 1961. This
article is highly recommended. Try Supt. of Documents, US GPO, Washington,
D. C. 20402, for" back issue at $1.
12 For an
approximation, double the takeoff angle for each halving of height.
Thus, at 14 Mc., 500 feet give 2°; 250 feet, 4°; 62 feet
16°, etc. To find the effective ground-reflection zone distance
and elevation relative to antenna mast height, plot a profile such
as Fig. 2.
13 Plane earth. For spherical-earth
ray studies, see Norton and Omberg, PIRE, Jan ., 1947.
14 Bailey, Bateman and Kirby. "Radio Transmission in
the Lower Atmosphere," PIRE, October 1955, p. 1226.
15 Bullington, "Radio Propagation
Fundamentals," B.S.T.J., May, 1957.
and Lane, "VHF and UHF Reception, Effects of Trees and Other Obstacles,"
Wireless World, May, 1955.
Posted March 2, 2014