Practical Amateur Aerial Design
July 1934 Radio News and the Short-Wave Article
of the nice things about antenna design articles is that regardless of when they were written, all that is needed
to make them entirely contemporary is to substitute a transistor schematic symbol for a vacuum tube and substitute
the units "kHz" and "MHz" for "kc" and "mc," respectively. If the article delves into detailed circuit design, a
substitution of "μF" for "mf" might also be required and depending on the frequency range, "pF" for "mmf" or
"μμF." Some readers might feel the urge to replace SAE units with metric units, but even a hundred years ago there
were people who needed to do that. "Aerial" and "antenna" are still interchangeable in modern radio parlance. With
that in mind, please enjoy this 1934 article on basic antenna design.
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Practical Amateur Aerial Design
The one big job for an antenna is to "soak up juice" from the transmitter and radiate as much energy as possible
into space. An antenna must be resonant and should be properly coupled to the power source
A. H. Lynch (W2DKS)
E. Glaser (W2BRB)
The type of antenna system to be used for amateur short-wave work is of secondary importance and depends largely
upon the individual location and the frequency bands to be covered in regular operation. Some types are easily adapted
for multi-band work while others are suited to only a single frequency band. In general, the latter types are somewhat
more efficient but not obviously so. The object of this article is to bring together some practical information
to help in choosing the most suitable antenna system for particular cases.
Better efficiency usually results
in using a Hertz antenna (1/2-wave wire in free space) than when using the 1/4-wave Marconi type which must have
a good ground system or a large counterpoise. (In this latter type every inch of wire in the system radiates energy,
so that a rather small percentage is radiated by the uppermost parts of the antenna which do the business.) The
horizontal Hertz, on the other hand, is entirely up-in-the-air so it becomes obvious why the efficiency is better.
And, of course, this applies equally well to signals coming in. Antenna systems for single-waveband operation will
be first considered.
This simple half-wave antenna diagrammed in Figure 1 is a split doublet, each side
being one quarter wavelength long. The length of each half equals 0.78 times the wavelength or 468 / (2 x frequency
It is ideal for portable work at any frequency and does a first class job for both transmitting and
receiving. The transmission line used to couple this doublet to the transmitter or receiver need not be tuned and
can be of any length provided its impedance is correct. Forms of rubber-covered, twisted lamp cord provide a suitable
"Giant Killer" feeder wire is intended especially for this purpose. Its impedance is slightly
higher than that at the center of the antenna (about 75 ohms) so that it should be fanned somewhat when connecting
to either side of the center insulator to be theoretically correct. This type of antenna is suited only to the waveband
(fundamental) for which it is cut or any odd harmonic thereof. On even harmonics a voltage (and impedance) maximum
appears at the center and cannot be matched to (is virtually short-circuited by) a 75-ohm line. When used for receiving,
the line will have no pickup and, therefore, a maximum signal-to-noise ratio will result. The line is magnetically
coupled to the receiver by means of a small primary coil; to the transmitter across a few turns of the last plate-tank
coil or coupled same as receiver. Bear in mind the necessity for sufficient insulation in the twisted line when
used for transmitting.
Another method of feeding a half-wave Hertz is to use a spaced transmission line
fanned at the antenna so that the impedance of the line equals that of a part of the antenna across which the line
is connected. See Figure 2. The length of this antenna and the distance between the wires are quite critical. The
length equals 463 / (frequency [mc.])
The distance (S) equals one-quarter the antenna length for a 600-ohm
line, and decreases as the line impedance goes down. See table in Figure 2. A transposed line may be used and is
particularly desirable for reception. The line should be perpendicular to the antenna for at least 1/4 wavelength
and should be terminated in such a manner at the transmitter so that it is balanced to ground. Transposition blocks
make an easy and efficient job of the feeder. In putting up this type of antenna, the wire should be several percent
too long and should be cut about one percent at a time, observing the performance after each cut. Fixed coupling
to the transmitter (or an oscillator) should be used so that the loading effect of the antenna might be seen on
the plate (or grid) milliammeter. When the doublet length is correct, it will have a maximum load effect.
A third type of antenna for single-band operation is the single-wire feeder affair shown in Figure 3. The length
of the antenna is roughly the same as the previous type but had better be determined by experiment, as previously
explained. The feeder should be connected one-seventh the length off the center and must run at right angles for
proper operation. There must be no sharp bends in this feeder or there will be reflection losses and line radiation.
This type is less suitable for reception than either of the foregoing systems because the line is not so free from
In the foregoing antennas, properly designed and constructed, there should be no radiation or pick-up
on the feeder and any length at all may be used. If no radiation or pick-up takes place in the feeder, the half-wave
antenna is doing all the work, which is exactly what we want. And in this case there is a marked directionality,
best transmission or reception being at right angles to the line of the antenna. In adjusting these antennas to
the transmitter, the plate meter must be used as the antenna current in the feeders is very low and is not necessarily
a true indicator of power taken by the antenna proper. Start with a minimum of coupling and gradually bring it up,
always retuning the plate-tank condenser, until the tube is properly loaded. It is possible to use any of these
types as a Marconi antenna for lower frequencies, tying the two feeders together. In a pinch this means may also
be used on odd harmonics of the Marconi quarter-wave fundamental but, at best, is a makeshift job.
antenna of Figure 3 may be used for all amateur frequencies but does not perform as well on harmonics as on the
fundamental frequency. This is because there is a mismatch between antenna and feeder on harmonics. It is possible
to compromise and improve harmonic operation but usually at the expense of fundamental efficiency. The feeder is
usually moved further from the center of the antenna. The feeder radiates, standing waves appear and there are losses
all around. Nevertheless, many hams like this method because of its utter simplicity and obtain good results with
it. It should be cut for the lowest frequency band to be used or, if this demands too great a stretch. Marconi operation
may be used on the highest wavelength, the antenna being cut for one band lower.
A second all-band antenna
may be procured by simply cutting any single wire (plus lead) into a half-wavelength for the lowest frequency band
to be used. Operation with a ground may also be used as above. This is really a voltage-feed type with a feeder
of zero length. The end of the antenna is plenty "hot" and should therefore be hung close to the plate on the tank
coil. A separate tank of low capacity (to reduce losses) may be coupled to the plate tank and the antenna hung on
to that. A ground is sometimes used at the other end of this coupled circuit. However, some losses are bound to
appear as the antenna comes into the shack and into the vicinity of other apparatus. Not only that but there is
a strong field around the antenna which may be a nuisance - affecting neutralizing, paralyzing the receiver, etc.
Of course, the entire length of wire radiates so that a lot of energy may be wasted before it gets to the high part
of the system. The length should be adjusted experimentally as with previous systems because the antenna proper,
coming into the shack, is subject to all kinds of influences which might affect the fundamental, or natural frequency.
This antenna is equally good on all harmonics because the ends of an antenna are always maximum voltage points (Figure
A third type, permitting many-band operation is the old, reliable "Zepp," (Zeppelin) which is about
the easiest antenna to resonate because a certain amount of tuning may be done right at the transmitter or receiver.
See Figure 5. A half-wave antenna is used with quarter-wave feeders. This might be considered a full-wave affair
with half a wavelength "folded," so that a point of maximum current comes right at the feeder end. This is a true
current-fed antenna, the losses appearing in the previous voltage-fed system being entirely absent here. Although
the feeders must be a quarter-wavelength long, electrically, much leeway is possible by loading or cutting with
parallel or series-tuning condensers. When multi-band operation is desired, a compromise in length must be made
to accommodate tuning to the various harmonics, the most reasonable length being a little under three-eights wavelength.
This is not at all critical, compared to the chopping of the flat tops for this family of antennas, but should be
quite close. This limitation of feeder length which appears here for the first time in this series of antenna systems,
might be worse were it not for the fact that the feeders may be bent or folded to add length. Again, the half-wave
flat-top might well be cut too long and chopped although this is less important with the Zepp than with most of
the other types. Most hams do not get a proper balance of feeder currents so the feeders do some radiating. Even
so, the results obtained usually justify this old favorite. It is because some leeway is possible that they don't
take the necessary pains to do n perfect job. This is really an unbalanced system, but it does a lot toward improving
the signal-to-noise ratio, especially when transposed feeders are used. However, in our opinion, the following antenna
is really the ace of all wave receiving aerials.
Figure 6 shows another very flexible system. this time
a balanced "split" arrangement that resembles the first shown doublet, but which is really a one-and-a-half-wave
antenna with two half-wave parts, folded as feeders. Since a current maximum exists in the center of the antenna
we need half-wave feeders this time, to get back to another current maximum for current feed. Again, compromising
in feeder length for the sake of the harmonic family, the feeders should be the same length as in the Zepp. This
will allow tuning to all bands in a similar manner. In both this type and the Zepp, the full voltage of the antenna
appears on the feeders, so that the spacers must be first-class insulators and of low dielectric constant. When
a transposed line is used this antenna is excellent for reception. although tuning must be used! This is the most
versatile aerial of the whole bunch for multi-band use and will cover a large part of the short-wave spectrum.
To correct a common fallacy, solid wire has not the lowest high-frequency resistance but, rather, a sort
of cable made of insulated wires, tightly twisted together, presents a much lower resistance than the equivalent
Posted August 13, 2013