September 1953 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.
If I had a copy of EZNEC software, I would try modeling
an end-fed "sky wire" antenna like the one described in this article and see how it functions when
driven from a location high above terra firma when the transmitter and receiver are connected to
Earth ground via some sort of wire. Author Norman Rowe operated from his attic as did
(and do) many
Hams. Although almost any reasonable mismatch can be accommodated with a proper matching circuit, that has
no major bearing on what the antenna radiation pattern looks like. However, the characteristics of
the ground circuit most certainly affects the antenna pattern. Surely someone like ARRL's
Joel Hallas (W1ZR), an EZNEC master, could
answer that without even having to run a simulation.
Come to think of it, I really don't know what a serious mismatch does to the power factor of the
voltage and current flowing in the antenna itself. Does the relative phase of current and voltage
always automatically correct itself in the antenna? If not, how does it affect the radiation
Let's Keep It Simple - Adjusting the Novice Antenna
Simple Voltage-Fed Wire for the Beginner
By Norman L. Rowe, K2DFW
For various reasons, the simple voltage-fed half-wave antenna has fallen into infrequent use. Nevertheless,
as K2DFW points out, it still remains one of the easiest skywires to install and adjust. From this consideration,
it is well worth considering by the Novice.
Fig. 1 - Sketch of the simple voltage-fed half-wave antenna.
This is written for the Novice who, like myself, has become somewhat confused by too much study.
Actually, I'm a very rusty old-timer from 'way back in 1921 when my ham station, 2BKK, blasted a broad,
channel somewhere in the vicinity of 200 meters with a half-kilowatt rotary-spark-gap transmitter. In
those days, the science of radio, by today's standards, was relatively simple. After thirty-two years
of complete indifference to the hobby, I am attempting gradually to crawl back through a maze of electronic
theory sufficient to flunk an "Einstein."
Take antennas, for example. Occasionally in the literature one can find a casual reference to an
end-fed antenna, and a guarded admission that good results can be obtained therefrom, but the experts
seem to devote most of their space to the half-wave dipole, or doublet. Then, they go on to 2-wire and
3-wire folded dipoles, impedance-matching transmission lines, flat lines, tuned lines, standing waves,
standing-wave ratios, line lengths, etc., etc., etc. What to do?
Of course, I do not imply that present antenna theory and practice is not right, but my shack, and
possibly yours, happens to be up in the attic and there is no easy way to string or tie into a center-fed
dipole. There certainly must be thousands of amateurs whose physical opportunities for antenna construction
are more favorable for an end-fed antenna and, who not only need a little assurance that this type,
under suitable circumstances, can be made just as efficient as the center-fed type, but who also might
use a little help in its design and method of erection.
To begin with, it should be noted that the most efficient way to couple a transmitter to an antenna
is by direct feed. In other words, move the transmitter up into the air and connect it directly to the
antenna. Obviously, this is often a physical impossibility. However, if your shack is located in an
attic room, or any floor high enough above the ground to be at usable antenna height, it is very easy
to accomplish this desirable objective by the use of an end-fed antenna.
Secondly, despite the emphasis in the literature of the desirability of feeding an antenna at a current
loop, it is not at all incorrect or inefficient to feed it at a voltage loop. So, if you place your
rig close by an attic or upper-floor window, you can direct-feed a half-wave antenna at one end (which
you know will be at a voltage loop) and get just as much DX as the ham next door using an equivalent
center-fed dipole and transmission line. Moreover, such an antenna is a cinch to erect and can be easily
adjusted to the correct length. (See ARRL Handbook Antenna Chapter section on direct feed.)
To avoid losses and other troubles, the end-fed antenna should be equal in electrical length to one-half
of the wavelength being transmitted. To permit multiband operation or the use of variable frequencies
within a band, some compromise in length must be made. However, we novices should not attempt to absorb
or experiment with everything all at once, and would do well to leave some of the complexities of the
science for a later day. In the beginning, let's try to keep it simple. Accordingly, we might temporarily
forget that there are other bands and other frequencies within a band and start out by buying an 80-meter
crystal somewhere within the Novice limits, and building a transmitter and antenna around it.
So, let's say we pick up a 3.74-Mc. crystal, build a small 2-tube 30-watt transmitter, and now desire
to erect an efficient end-fed antenna for connection thereto. The Handbook states that e actual physical
length of a half-wave antenna may be calculated by the formula L = 468/f, where L = length
in feet, and f = frequency in megacycles. Hence, our antenna should be exactly 125 feet long.
However, the proximity of trees, buildings and other structures, and the height above ground - to mention
just a few things - have an influence on the electrical length of this antenna, and it is virtually
impossible to calculate in advance for all Novice locations the exact length required for best antenna
performance for a 3.74-Mc. crystal.
So, if this situation fits your case, here's what you do. Attach one end of your antenna to a distant
tree, barn, house, or pole by means of an insulator, clothesline, clothesline pulley and weight, and
bring the other end to a convenient point above or alongside your attic window as in Fig. 1. Start out
with about 120 feet of wire between insulators and, without cutting it, lash the balance of the coil
of antenna wire temporarily to the insulator outside the window. The stranded type antenna wire is preferred,
since it is more flexible than solid wire and therefore easier to handle. However, other types of wire
may be used, provided it is bare so that the turns of excess wire are shorted out. The lead-in should
be as short and direct as possible, since this actually is an extension of the antenna. It is made by
unrolling the free end of the coiled wire.
Next, tune up your transmitter without the antenna connected.
Note the setting of the antenna tank-condenser dial when resonant at 3.74 Mc. The coupling between the
final and antenna tanks should be loose enough so that there is only one peak in plate current as the
antenna tank circuit is tuned through resonance. Then attach the antenna lead-in to one end of the antenna
tank coil, press the key and note whether or not there is any difference in the reading of the milliammeter
indicating amplifier plate current. If so, do not readjust the output tank condenser but retune the
antenna tank condenser to resonate the antenna and note the dial reading when the plate current reads
maximum. Then, reach out the window and pull in two or three feet of antenna wire, coil it up, lash
it to the insulator and repeat the above procedure. If the dial reading of the antenna tank condenser
when tuned to resonance with this shorter antenna is closer to the dial reading at resonance without
the antenna connected, you are proceeding in the right direction. If it is farther away, you need to
lengthen rather than shorten the antenna.
By trial and error, all very easily performed without leaving the shack, you will finally arrive
at the physical length that is electrically one-half a wavelength long. This may be determined when
the dial reading of the antenna tank condenser at resonance is the same whether the antenna is connected
to or disconnected from the rig.
After the correct length has been found, the antenna coupling can be increased so that the amplifier
will draw the desired plate current when the antenna tank circuit is tuned to resonance.
Now, brother, you're "putting out!" Since an end-fed half-wave antenna is voltage fed, it is important
to insulate the lead-in well as it passes through the window, or frame, in order to avoid excessive
dielectric loss at this point. No ground connection is needed, although it may be desirable for lightning
After the proper length of your antenna is determined, remove the coil of excess antenna wire, and
solder the joint to the short lead-in. It is well to leave the clothesline, pulley and weight at the
far end, especially if attached to a tree, since this will prevent wind damage.
By some slight additional adjustment of length, such an antenna may be readily converted for use
on 40 meters by the same trial-and-error method. In this case, it will operate as full-wave, or second-harmonic,
antenna, but will still be voltage fed.
To make it easier, later on, to shift back and forth between 80 and 40, it is better, when possible,
to string a separate wire for 40 meters between your attic window and some other object not too parallel
to the 80-meter wire. Start with about 60 feet of wire between insulators and follow the same length-adjustment
At some possible sacrifice in performance, the same idea can be used for operating rooms located
below the level of the antenna. Under such circumstances, the length of wire between insulators is reduced
to compensate for the added length of lead-in wire, the over-all length, from the far end of the antenna
to the antenna tank coil, being the determining factor.
For your receiving set, a random length of wire in the attic will usually bring in anything you can
reach with a Novice low-power rig.
So, up the trees, men, and let's keep it simple.
Posted August 15,2016