August 1940 QST
Table of Contents
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 are hereby acknowledged.
On a fairly regular occasion someone will
write to one of the QST magazine columnists or post on a forum asking about
information on a particular antenna configuration he recalled seeing printed many
moons ago, but can no longer find anything on it. Fortunately, the columnists are
guys who have been in the Ham game for a many decades and not only remember what
the writer references, but knows where to dig out the original info. Even with the
plethora of resources available on the Web, some things still cannot be found because
nobody yet has posted it. That is one of my prime motivations for doing what I do
- that is to help make useful data available. That is the reason I also scan and
post schematics and service pages for vintage radios.
The Fixed "Rotary" Beam Antenna
Fig. 1 - The fundamental" pitchfork" antenna system, such
as is used at W2USA, is shown at A. Two pitchfork antennas can be combined, as at
B, to give coverage in directions along two lines at right angles to each other.
The elements are vertical in both cases.
Variable Directivity With Fixed Antennas
By Arthur H. Lynch* W2DKJ
Although the antenna systems described in this story are not exactly brand new,
many of the ideas regarding installation and operation are, and you're bound to
garner food for thought from these pages. The amateur with a lack of roof space
will find it particularly to his liking.
It all came about in the following manner. Our good friend, W2BKX, bought himself
a house in Garden City, L. I., and restrictions regarding antennas are just a little
bit tough in that town. George, who had been doing some excellent work with low
power on 10 meters from his location on the roof of a lofty apartment in New York
City, wanted to duplicate the performance in his new home. Lacking the height of
his old location, we knew it would be necessary to go to some form of beam. The
usual "hay rack," suitable for a three- or four-element horizontal rotary, was out
of the question.
Whenever occasions like this arise we can't avoid remembering the shock we all
got from the performance of the vertical 20-meter "pitch-fork" antenna that was
used at W2USA for so long, before the full-wave vertical rotary was erected. The
former, which was the same as the antenna of Fig. 1A, was set right on the
roof of the building. The roof was made of metallized roofing paper, and it furnished
a very effective counterpoise. The beam, made of Premax aluminum units, was set
up along an east-west line, and it gave us a grand signal in those directions, but
we were surprised to find that the beam was not too sharp and that we were getting
out in nearly all directions except at exactly right angles to a line through the
That experience, coupled with the reports of others who have tried the three-vertical
system1 for securing transmission in all directions, led us to the conclusion
that more might be accomplished with the method than had been considered previously.
Instead of confining the beam to single-band operation we decided, in George's case,
to try the same arrangement on all the bands which he would desire to work. Since
the lowest-frequency band he uses is 28 Mc., the 10-meter band was used as the starting
point for calculations. The use of tuned lines was dictated by the multi-band operation,
but this has the advantage that the system can even be used on the next lower frequency
band with, of course, some compromise in performance. However, it should be remembered
that we are attempting to get the most out of the least and, while it is recognized
that it is possible to design an antenna with the same number of elements which
will do a better job in anyone direction and on anyone band, we believe that the
many uses to which this system can be put warrants its consideration by anyone with
limited antenna space.
Fig. 2 - If room is available, two pitchfork antennas can
provide good coverage by separating them on the house-top, as shown at A. Suggested
construction of the feed line is illustrated at B, and the antenna coupling detail
is shown at C.
Fig. 3 - Plan view of the supporting framework of the 14
Mc. pitchfork antenna at W2USA. The members are made of 3-inch by 10-inch stock;
A is 10 feet long, B is 4 feet long, and C is 5 inches long. For 28 Mc., the members
can be 2-inch by 4-inch stock, with A 6 feet long, B 2 feet long, and C 4 inches
long. In either case, the supports are held fast by sandbags laid on them.
The pitchfork antenna has, of course, a null along the line at right angles to
the plane of the elements. This null can be overcome by using a third element as
shown in Fig. 1B. By selecting the proper pair of elements, the signal can
be radiated most effectively in any desired direction while still retaining the
gain of the system. Naturally, either pair of elements can be used with equal effectiveness
along a line making an angle of 45° with the line of the plane of the elements,
but in any other direction a particular pair will be more effective.
If room is available for the erection of two separate beams a half wavelength
or more apart and at right angles to each other, it would be well worthwhile, and
the directional pattern would be nearer the pure theoretical one than is possible
with the compromise system using three elements. Many of the houses in the larger
cities have roof space of 25 by 40 feet or more, which is plenty of room for the
use of two pitchfork antennas, as shown in Fig. 2. When less space is available,
it is necessary to go to the system shown in Fig. 1
In W2BKX's case it was necessary to use the compact system using three elements
(Fig. 1B). Since the mechanical arrangement used on that job may be of help
to others, it is given in more than ordinary detail later in this story. At first,
consideration was given to the possibility of using a single antenna coil for each
band and placing the antenna relay at the ends of the four lead-in wires, using
link coupling to the antenna coil from the final tank and tuning the feed line with
two series condensers and a third condenser in parallel. However, the final arrangement
shown in Fig. 2C is very much more effective and easy to control, although
it requires a bit more apparatus. In addition to providing suitable operation on
anyone band it allows the use of both antennas at the same time, for general coverage
use when calling CQ.
For convenience, the two transmission lines are carried by the same separators.
Old-fashioned cage antenna spreaders (which are still available in some radio stores)
can be used, or curtain rings of celluloid, Bakelite or well-varnished wood can
be drilled to take the wires.
Whether the triangular set-up with three vertical elements or the two spaced
pitchfork antennas are used has no bearing on the feed system or the tuning of the
two antennas and, for this reason, the two cases have not been treated separately.
When two separate pitchforks are to be used on only one band, a quarter-wave matching
section and any type of non-resonant line is probably the best method of feed -
the tuned line is described in this case because we were interested in multi-band
Where two elements are to be used in a single pitchfork set-up, which is all
that is required in many locations, it may be well worthwhile to take a page from
the book of construction of W2USA and use the simple framework shown in Fig. 3.
If two separate pairs of verticals are used, two similar frames can be used. This
form of construction makes the use of nails, lag-bolts or other fastening directly
to the roof unnecessary. Sand bags will do very well for anchors. If a coarse bag
is used, it will be found advisable to use coarse sand. In some instances, we have
found it desirable to add a little cement, so that the bags will take the form of
the supports and harden in that shape.
Fig. 4 - Plan view of the supporting platform for a three-element
14-Mc. fixed" rotary" beam set on a flat roof. The frame can be held in place by
Where three verticals are to be used to provide the" rotary" effect and they
are to be set up on a flat roof, the layout shown in Fig. 4 will be found desirable.
Where 20 meters is the" fundamental" frequency of the system, the vertical elements
will be approximately 29 feet high, and the supporting structure should be reasonably
heavy. Planks of warp-free, well-dried, solid wood, 3 inches thick and 10 inches
wide, are suitable for this use. The lengths are indicated in the drawing.
Where 10 meters is to be the lowest fundamental frequency, the vertical elements
will be of lighter material, less than 15 feet high and only 4 feet 4 inches apart.
For that reason regular 2 by 4 stock, half the lengths indicated in Fig. 3,
will do very nicely on 28 Mc. It will be noted that plenty of room has been provided
for the use of sandbags, since their liberal use may be warranted if the array is
going to be subjected to high winds. The blocks at the ends of the small members
are made of the same lumber which is used for the other members and provide equalization
for those portions of the structure which are above roof level.
Where we have a flat roof to deal with, the problem of the fixed "rotary" beam,
except for the manner of running the transmission lines away from the structure,
is relatively easy. However, where we have to set one of the three vertical assemblies
on a peaked roof, we have a horse of another color. In the accompanying drawings,
Figs. 5 and 6, two alternative methods are shown. In the side elevation, it can
be seen how the weight of the assembly is distributed and how the outside ends of
the cross member are supported by the roof.
Most of us are not sufficiently clever with carpenter's tools to make such a
structure without having the joints badly askew. It is really surprising to find
what a great help strap hinges can be in such circumstances. A quarter of an inch
here or there or a badly cut angle on the end of a supporting strut would ordinarily
throw the whole beam out of kilter, while hinges, used as indicated in the top view,
permit us to do the trick quite easily. Before attaching the hinges to the various
members, we should be sure to place them so that they will ride over the centers
of the roof studs, where the weight will be carried without the possibility of punching
a hole through the shingles or other roofing material. Another important advantage
resulting from the use of hinges for this purpose is that it is difficult to make
screws or bolts hold when we put them through one surface into the butt-end of another
member, while using the hinges makes it possible to set the screws into side surfaces
at all times, with better distribution of the stresses and providing greater strength
as well as ease of assembly.
Fig. 5. - Two different methods for mounting the three-element
fixed" rotary" on the peak of a roof. The use of hinges offsets any minor lack of
Fig. 6 - The framework used to support the three-element
29·Mc. antenna at W2BKX' The small side view more clearly shows how the hinges simplify
The assembly which we designed for use at W2BKX's new location is a simple square
made of two by four stock. It wasn't the easiest thing in the world to set it up,
because the house doesn't aim just right to get the proper directions for the beam
without putting the supporting frame at a cock-eyed angle with relation to the roof
lines. Then, too, the roof is slate (and, besides, it's George's new house), so
we couldn't go banging nails here and there, as we have been accused of doing on
other occasions. (The story is much exaggerated and we have not done any such thing.
The bedroom ceiling fell down as the result of what we know was a poor roofing job,
but which we can never prove was not the direct result of our excursions about the
Fig. 6 gives the details of the assembly, and it will be seen that we have
again gone very strongly for the use of hinges. Even a poor carpenter can do a fairly
respectable job of setting up such an assembly by using hinges generously and a
spirit-level frequently. The 6-foot planks of 2 by 6 were first laid side by side
along the peak of the roof, after they had been held together by a couple of hinges.
That gave us the support for most of the weight and the rest was relatively easy.
More hinges, attached to the ends of a pair of 2 by 4's which were in turn attached
to the outside west wall of the house, gave us the bracing for the ends, and other
hinges held the remainder of the framework to the two long planks. The sandbag draped
over the east end of the whole job goes a long way toward holding things under control,
even in a high wind.
In this case, the matter of bringing the transmission lines down has been made
relatively simple because they drop in a straight line to a point outside the radio
room window. Insulators, suitably disposed along the small cross strut give the
lines a good start. The feed line is made up as previously described (Fig. 2-B),
and is run down the side of the house. A bracket outside the window supports the
other end of the line.
Reference has been made to the effectiveness of beams of this nature being improved
when it is possible for us to erect them adjacent to flat metal roofs, where the
roofing acts as a counterpoise. However, very much the same effect can be had, even
when we are located in a frame house having a shingle or other form of non-metallic
roof. If it is possible to get into the attic, it is only necessary to procure some
metallized insulation paper, which carries the trade name "Reynold's Metallation,"
and tack it up on the rafters. It comes in two kinds. One has metal on only one
side and the other type has aluminum foil on both sides. We "got it wholesale" so
nothing was too good and, instead of providing ourselves with the usual size counterpoise,
we covered the whole inside of the attic, using the bi-metal type of paper, of course.
It works very well for what we set out to do with it, and it really does hold the
heat out in summer and in during the winter. It brings another blessing by carrying
any possible leaks in the roof to some portion which is not graced by some form
of antenna support. So, if you think a counterpoise would be of any advantage to
you, it might be a good idea to "sell" the family the idea of insulating the attic.
But be very careful that they don't hook you with the idea of using some form of
non-metallic wall board and then let you have the job of finishing off the attic,
which has been under consideration for so long, leaving you without your counterpoise.
* Managing Director, W2USA Radio Club, World's Fair, New York
1 Lynch, "Feeding Vertical Antennas," QST, Jan., 1939.
Posted June 10, 2021(original