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
September 1966 QST
These articles are scanned and OCRed from old editions of the
ARRL's QST magazine. Here is a list of the
QST articles I have already posted. All copyrights (if any) are hereby acknowledged.
See all available
vintage QST articles.
Station Design for DX - Part I
Part I - Antenna Topics and Siting
BY Paul D. Rockwell, * W3AFM
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 are:
Furthermore, 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
Another topic 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.
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.
W3AFM 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.
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 inferior performers.10
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
The formula for angle of maximum radiation (horizontal
antennas, flat terrain) is
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
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
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.
Incidentally, ground 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 these.
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,
2 Anderson, "Antenna Behavior over Real Earth,"
QST June, 1965.
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.
4 From 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.
7 Orr, Quad Antennas,
Radio Publications, Wilton , Conn. 1959.
Test Procedures for Antennas," IEEE Transactions on Antennas and Propagation,
Vol. AP-13, No.3, May 1965, pp. 437-466.
Viezbicke, Interactions between Nested Rhombic
Antennas," NBS Report 6773, Sept. 12, 1961.
"Performance of an Inclined Vee Aerial," PIRE, Australia, Sept. 1963.
11 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.
Bullington, "Radio Propagation Fundamentals,"
B.S.T.J., May, 1957.
16 Saxton and Lane, "VHF and
UHF Reception, Effects of Trees and Other Obstacles," Wireless World,
Posted March 2, 2014