Station Design for DX - Part II
October 1966 QST Article
I of this article appeared in last month's (September) edition. It introduced
concepts in antenna types and siting. This second part talks about cost
tradeoffs for various aspects of a DX setup. Author Paul Rockwell does
a nice job of providing graphs of cost versus performance increases
for transmitter power, antenna gain, tower height and constructions,
etc. He uses prices typical of the mid 1960s, but even without knowing
the equivalent modern day equipment prices, the shapes of the curves
are good indicators of where the point of diminishing returns exists.
October 1966 QST
of Contents]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.
Paul Rockwell wrote a 4-part series on station design for long distance
(DX) communications that covered antenna selection and siting
I), economics and construction
station configuration and receiver topics (Part
III), and propagation quirks and operating tips
See all available
vintage QST articles.
Station Design for DX - Part II
Part II - Economics of Station Design and Construction
D. Rockwell, W3AFM
In the pursuit of amateur radio, dollar limitations are always present.
What is the most practical allocation of available funds? Let us first
illustrate an analytical - approach to this question from the standpoint
of effective DX-radiated power (DX e.r.p.). Assume 20-meter operation,
flat terrain, no voice modulator, and optimum radiation angle of 1°.
As a frame of reference, 0-db. will be taken for 100 watts c.w. input,
30-foot tower height, and 10-foot Yagi boom-length.
Fig. 3 - Transmitter power costs.
power costs run about as shown on Fig. 3. The costs include driver,
but exclude v.f.o. The curve would have to be shaded upward for first-class
features, and downward for some home constructors. Make your own curve,
if you prefer. What is being shown on this and the following curves
is a design technique - not a universally applicable set of data. What
is important to note, in this example, is that the last db. (from 780
to 1000 watts) costs $100.
Now consider antenna costs. Fig.
4 presents these for Yagis. The db. gain values are relative to a half-wave
dipole, same height and foreground. The next db. beyond 30-foot boom
length costs $200. Stacking two beams, which gives 3-db. gain at the
expense of 40-foot additional tower height is attractive beyond about
30-foot boom length. However, this introduces the problem of rotating
both beams without interfering with guys. The Telrex Big Bertha solves
this by rotating a self-supporting tower. Such a tower, 112 feet high,
equipped with antennas and accessories, costs over $15,000 in place.
Now tower height. Fig. 5 presents costs, based on $10 per foot
for ordinary lattice tower, guys, anchors and foundations. Erection
costs are added, beyond 40-foot height, up to $400 for the 150-foot
height. No allowance is included for rotator, indicator, insurance,
etc. Gains are related to the assumed ideal of 1° takeoff angle
by use of the image-antenna geometric construction. Analysis by the
indicated technique shows that, to a close approximation, DX e.r.p.
at 1° increases as the square of tower height. That is, each time
the tower height is doubled, 6-db. improvement is appreciated. Because
DX signals often arrive (and should be transmitted) at angles considerably
above 1°, this figure must be weighted downward. Fig. 5 has been
constructed on the basis of linear relation between e.r.p. and tower
height - 3-db. improvement for each doubling of height. This agrees
fairly well with Utlaut's results for very high effective heights.
The concept being developed is: Cost per db. for the last db. of improvement
which can be handled economically. Suppose we can afford
Fig. 4 - Antenna costs.
Fig. 5 - Tower Costs.
the last db. By examination of the curves, we see immediately we should
run 1-kw. input, for in this department the last db. costs only $100.
We choose from Figure 4a boom length of 40 feet. Tower height per Figure
5 is 75 feet. Total cost, adding the corresponding ordinates of Figures
3, 4, and 5 is $1980.00.
Perhaps this cost exceeds our means.
Maybe we can afford only $50 for the last db. in each of the three departments
principally affecting DX effective radiated power (DX e.r.p.). On this
basis, we choose 150 watts, 23-foot boom, and 40-foot tower height.
Total cost is $350.00.
Once the concept is understood, curves
may be developed to fit the individual situation, and to take in to
account all sorts of other variables: cable losses, fixed costs for
auxiliaries, commercial increments of sizes, nested-rhombics-plus-real-estate
versus Yagis, etc.
An important consideration, so far excluded
in order to simplify the discussion, is the fact that antenna db. work
both ways: send and receive. Appraisal of antenna and tower costs for
DX e.r.p. should therefore be weighted, so as to allocate a share of
these costs to the receiving advantage. A reasonable factor is one-half.
That is, the dollar values of ordinates of Figs. 4 and 5 can be cut
in half, for economic optimization of design with respect to DX e.r.p.
only. On this basis, Fig. 6 shows optimum combinations as a function
of funds available. The figure is constructed by assuming various dollars-per-last-db.
values, and connecting the resultant values by curves. Of course the
optimization differs somewhat from the $50/db. and 200/db. examples
above, because the receiving components of costs have been broken out
For example, suppose $500 are available for the
relevant parts of the station. Refer to "Total Cost" on Fig. 6 at $500.
Draw a line straight up. Parameters are: Power, 150 watts; Boom, 27
feet; Tower, 50 feet. Gain relative to the reference installation is
If $2000 are available, parameters are: Power, 1 kw.;
Boom, 40 feet; Tower, 75 feet. Gain relative to the reference installation
is 17.2 db.
Fig. 7 presents compatible equipment complements
with regard only for DX e.r.p. - no allowance for concurrent receiving
advantages. This represents a more conventionally accepted approach.
In effect, transmitter power is given greater initial emphasis. These
db. are cheap and more convenient than antenna/tower db., but do not
bring corresponding receiving advantages. After the legal power limit
is reached, optimization proceeds much as on Figure 6. For $500, read
off: Power, 275 watt; Boom, 26 feet; Tower, 44 feet: Relative gain,
7.3 db. For $2000: Power, 1 kw.: Boom, 40 feet; Tower, 75 feet; Relative
gain, 17.2 db.
Economically, c.w. telegraphy gives by far the
most DX per dollar. Not only is this true because more DX stations are
available by c.w., but also because of greater efficiency, expressed
in db. as follows 17:
D.s.b. a.m., order-wire quality... +17 db. required
order-wire quality ........... + 14 db. required
will nearly all aver that the table above should be corrected to read
"11 db." instead of "14 db" for s.s.b.
After reading this, it
is fair to ask: "What does a db. in DX e.r.p. really buy, after all,
in terms of DX capability'?" The answer is that, other things being
equal, it buys a lot. Six db. buy, competitively, a decisive advantage.
So far, system-design trade-offs have been discussed. The matter
of constructional alternatives is also important in station economics.
The remainder of this month's text is on miscellaneous antenna-construction
comments. Antenna mounts are frequently the major item of home built
First, re antenna towers. There are fine products on the market. These
firms also sell the numerous necessary and desirable accessories: brackets,
clamps, clips, anchor, winches, guys, and even gin poles. Only a small
percentage of DXers use these products, because the majority (a) can't
afford them, and/or (b) home and neighborhood consideration won't permit
them. Speaking in generalized terms, short of all-out optimum performance,
a practical and almost universally applicable construction is to use
telescoping pipe sizes, side-supported to the house, with a hand-winch
for running the antenna up and down. This is what is done at W3AFM.
Some particulars follow.
Fig. 6 - Compatible equipment complements (with allowance for
The cheapest and most universally available
mast structural element is water pipe. It comes in 21-foot lengths.
It should be ordered black, unthreaded. Local suppliers usually deliver.
Prices run about $10.00 a length, depending on weight. Figure 12¢
to 20¢ a pound, depending on discounts, location etc. Sizes are
confusing, because they are based on nominal i.d. of the standard weight.
"Extra strong" and "double extra strong" are of the same material, but
smaller i.d. (same o.d., to match fittings) for greater wall thickness,
Some examples are given in the table below, in which "XXH" means "double
Yagis are made to mount on 1 1/2-inch pipe. Speaking in generalities,
and depending on prevalent winds, antenna, etc., 16 feet of unsupported
height (i.e., 16 feet above guy attachment or last bracket) can be good
design, whereas 20 feet can be risky. It is wise, if using water pipe,
to telescope section, in such a way that the top 10 feet are single-wall,
next 10 feet double-wall, next 1 foot triple-wall, etc.
much better than water-pipe iron exists. Chrome-molybdenum electroweld
or seamless AISI 4142, heat-treated to 180 k.p.s.i. looks great - but
costs ten times as much per pound and seems almost impossible to get
in less than mill lot.
A popular mast in the Northeast is Diamond
"E" (1020 cold-drawn steel) 2 inches o.d. by 0.25-inch wall X 20 feet
long, selling for about $60.00. So far as known, one of these has never
Aluminum alloys have a modulus one-third that of steel. This can make
them very willowy, unless kept short, and thick-walled.
Fig. 7 - Compatible equipment complements (DX e.r.p, optimization).
best installations, the mast or top tubular-section of the antenna-mount,
projects only a few feet above the main steel-lattice tower. The rotator
is then a few feet below the top of this tower. Sometimes, for reasons
previously mentioned, a lattice tower is not practical. In such cases,
the pipe mast is extended down to the ground, and the rotator mounted
near the ground. Such an antenna support is commonly clamped, loosely
so the antenna can be turned, to the side of a house. When this is done,
it is important to spread the stress on the house structure. This is
done by angle-iron, channels, or wooden members, coupled typically by
1/2 inch threaded bolts all the way through, for example, the attic
walls. At W3AFM, a vertical 2 inch X 6 inch X 12 foot plank is bolted
to the side of the house, with 2 inch X 4 inch X 6 foot lateral stress-spreaders
horizontally inside the attic wall. The strongest wood commonly stocked
is oak. Clear white oak, unfinished, and suitably stained, is used.
The vertical plank is attached by four 1/2 inch bolts, and projects
4 feet above the peak of the roof. Three husky electrical clamps attach
the mast to this plank. The second 21 foot pipe section up from the
ground is slotted to fit over a 1/2 inch dowel in the lowermost 21 foot
pipe section; so the antenna may be lowered to a height reachable from
the roof by first raising it a few inches, then lowering the disengaged
part to the ground. Such a load requires work advantage. Boat winches,
available from Sears or Ward's at about $25.00, are well suited to this
purpose. Half-inch polyethylene boat rope is a good value.
can be dangerous and expensive to economize on small hardware fittings:
eyebolts, U-bolts, clamps and the like. Items stocked at Sears, Ward's
and neighborhood urban hardware stores generally go only to 3/8 inch
sizes, and are cheaply made. For example, a 3/8 inch eyebolt, of the
kind having a formed, unwelded eye, if used at the top of the vertical
plank mentioned above, could easily unwind and drop the load on the
ham below at the boat winch. Where does one get better hardware? Try
industrial suppliers, such as McMaster-Carr Supply Co., 2828 North Paulina
Street, P.O. Box 4355, Chicago, Illinois 60680.
An item not
as widely known among amateurs as it should be is the screw anchor.
This is a long rod with eye at one end and an auger plate at the other,
by which it is screwed in to the ground. A common size is the Hubbard
7526 or Chance 6346, 66 inches long, 3/4 inch rod, 6 inch blade, which
sells for about $5.00. Fully screwed into good soil, these withstand
4500-pound pull. Many varieties are made: swamp anchors with blades
15 inches in diameter; rock anchors, etc. A well-stocked supplier is
Graybar, with warehouses in most U. S. cities. Graybar also has excellent
ground-rods - not as cheap as you see in radio stores - but better.
Typical sizes are Hubbard 9348, 5/8 inch in diameter X 8 feet, or Hubbard
9,450, 3/4 inch X 10 feet. They even make one (No. 9697) 1 inch in diameter
X 40 feet long. Graybar also stocks clips, clamps, thimbles, arming
bolts, eyebolts, shackles, etc.
If the terms used above, and
other such as: "gin pole," "tag line," and" come-along" are unfamiliar,
some preliminary reading or talking with persons having experience in
rigging, is desirable prior to undertaking a major antenna project.
Alternatively, there are people who, for a fee, will take the problems
off your hands.
Rescue squads or fire departments which accept
public contributions, can be helpful in raising antennas to the top
of, say 60, foot towers or poles. A local amateur made a $25.00 contribution
(tax deductible?) and found willing and effective cooperation.
Raising a tower with a crane can be dangerous, though it is common
procedure commercially. A 130 foot, 24 inch tower was once being raised
with a 60-foot crane by wiring the tower base to its concrete foundation,
and picking up the tower by attaching the crane hook below the tower
center. The base temporary wires failed. The tower base whipped sidewise
and killed a rigger instantly.
Locally, the most experienced
ham riggers, W3MSK and W3GRF, prefer to assemble towers such as the
AB-105 vertically in place by carrying up pieces, bolting them on, climbing
up to the next level, etc., using a light gin pole and ground helpers
to pull up materials as required.
The reason why self-supported
high towers are rare compared to guyed towers, is that they cost several
times as much. (The next installment will appear in an early issue.)
17 "Median Signal Power
Required for Reception of Radio Transmissions in the Presence of Noise,"
Technical Report 5, U.S. Army Radio Propagation Agency . .June, 1961.
* Costs in parentheses are used
for apportionment purposes in construction of Fig. 6. Total costs in
all cases are taken from the left ordinate.
Posted February 28, 2014