antenna (usually referred to as a Yagi), is a relatively simple to construct multielement
structure consisting of a combination of driven (director) and reflective (reflector)
dipoles. Careful phasing of the configuration results in a directional radiation
pattern that is used often for long distance (DX) and direction finding work. It
is also useful in a dense signal environment where there is a need to exclude received
signals not emanating from a preferred source. Common (or what used to be) rooftop
television antennas were of the Yagi type and served not just to pull in distant
stations, but to help reject multipath signals that would cause ghost images on
the screen. The concept is the 1926 brainchild of Messrs. Shintaro Uda and Hidetsugu
Yagi, both of the Tohoku Imperial University, in Japan. The Yagi antenna
described in this 1952 issue of Radio & Television News magazine is for
VHF channels 2-13.
The Yagi Television Antenna
By M. G. O'Leary
Fig. 1 - Over-all view of the author's home-built Yagi antenna
designed for the fringe area reception of Channel 5, Syracuse. Director tuning stubs
are clearly visible.
Construction details for building your own fringe area antenna. Although designed
for Channel 5, data is included to cover any of the v.h.f. TV channels.
Kingston, Ontario is 75 miles north of Syracuse, N. Y. With a booster and high-gain
antenna, reasonably good pictures can be obtained from WSYR, Channel 5, and WHEN,
Chanel 8, even during the poor winter months. However, good antenna installations
are costly; mounted on a 20 ft. roof-top mast, one single-channel Yagi costs about
$60.00, while two, one for each channel, run at $90.00. Homemade installations can
be completed for from $10.00 to $15.00.
It was the author's chore to design Channel 5 antenna for a friend who intended
to construct it himself. The results of our joint efforts were highly successful
from the performance as well as the constructional point of view. The pictures obtained
are equal to, and in some cases better than, those obtained from several commercial
installations. The finished product weathered a recent bad sleet storm intact, while
many other antennas in the vicinity were badly damaged. Readers living in fringe
areas who intend to build their own Yagis should be able to benefit from some or
all the ideas that were worked out for this design.
Deciding on the type of antenna to be used was the first problem. Lack of space
ruled out the highly desirable rhombic design.1 A horn type2
was mighty attractive, especially because of the very high gain on Channel 8 as
well as the adequate gain on Channel 5, but the structure was to be mounted on a
small bungalow and, from the purely aesthetic point of view, its size precluded
its use. Five-element Yagis and stacked conicals with reflectors have proven themselves
in this area, and our choice boiled down to either one of these types. The Yagi
was finally selected - for two reasons: robust construction is much more easily
achieved, and the experience of others suggested that this type picked up less noise.
The design of the Yagi turned out to be a very complex matter. Two ready-made
designs were available, one for single channels, the other for reception of both
Channels 4 and 5.3,4 We were looking for something more robust than the
former, and a previously-constructed model of the latter had been found to set up
substantial amounts of standing waves in the feedline when Channel 5 was being received
- probably due to a lack of preciseness in the wiring of the rather critical feed
arrangement. A third article was consulted but constructional details were lacking.5
The "Radio Amateurs' Handbook" contained much helpful information but did not delve
too deeply into the problem of the five-element Yagi.
Fig. 2 - Construction details on the tuning stubs shown in
over-all diagram (Fig. 4).
Fig. 3 - Method of fastening antenna elements to 1" square
#61ST alloy tubing.
At this point we were somewhat discouraged by something we could not then comprehend.
There was a seemingly serious discrepancy from article to article on the feed point
resistance of the Yagi antenna. The "Handbook" stressed that the resistance of the
dipole was substantially reduced by the addition of parasitic elements. Yet some
of the other articles were claiming figures of 200 to 300 ohms for five-element
folded dipole arrays. Luckily, an issue of "QST" was at hand with two excellent
articles on Yagi design.6,7 From these it was learned that reflector
and director spacings and lengths had significant effects on the antenna feedpoint
resistance, bandwidth, front-to-back ratio, "Q," and dipole resonant frequency.
While the information given covered only two- and three-element arrays, it was decided
to use it as the basis for a five-element design.
However, it was apparent that there were many pitfalls in designing a multi-element
antenna without laboratory test equipment. Thus we decided that our antenna would
be one that could be easily adjusted to peak performance. Reference (6) used graphs
to show how director lengths and director-dipole spacings (with a director-reflector
spacing constant at 0.3 wavelength) affect bandwidth, feedpoint resistance, and
"Q" of a three-element Yagi. If these graphs are studied, it is apparent that an
adjustable director length can only vary all these values over wide limits if the
director-dipole spacing is fixed at 0.1 wavelength. (The dipole-reflector spacing
is then 0.2 wavelength.) For our purposes we assumed - guessed may be a better description
- that two additional directors would have the same effect, to a lesser extent,
as the one director. At any rate we fixed our director-dipole and reflector-dipole
spacings at 0.1 and approximately 0.2 wavelength respectively, and estimated that
if all director lengths were adjustable, we would have adequate control. Reference
(7) shows by graphs how varying the director or reflector lengths will change the
dipole resonant frequency and it thus seemed desirable to incorporate a length adjustment
in the dipole.
The design finally worked out called for the following:
1. A three-conductor folded dipole to raise the feed point resistance sufficiently
so that it could be adjusted to around 300 ohms, thus properly matching 300-ohm
2. A dipole of variable length.
3.A 0.53 wavelength long reflector spaced approximately 0.2 wavelength from the
4. Three directors, all spaced 0.1 wavelength, and all adjustable in length.
5. An easily adjusted open quarter-wave matching stub at the dipole feedpoint.
This will be discussed later.
For ruggedness, 5/8" dia. 24ST tubing was used throughout. 61ST alloy should
be a satisfactory substitute, but it is recommended that such alloys as 24S.0, 61SW,
61S0, 2S, and 3S be avoided unless the wall thicknesses are very heavy. The boom
was made from 61ST 1" square tubing. Round tubing can certainly be used for the
boom, but the "squaring-up" will be much more difficult.
Fig. 4 is a diagram giving all Channel 5 dimensions. These dimensions were
computed using the formula
K is obtained from the "Handbook." Fig. 10-44 of my 1948 edition graphically
shows the effect of antenna diameter on half-wave resonant length. To find K for
5/8" tubing in Channel 5 design we first compute
Fig. 4 - Dimensions for the Channel 5 Yagi. Figures are given
for the element lengths with and without matching and tuning stubs. See Table 1
for other channel dimensions.
For this 122 ratio K is taken from the graph to be 0.93. This value is used in
determining the physical length of the 0.53 wavelength reflector. K for the dipole
is less than 0.93 due to the three closely-spaced conductors, but the actual value
is difficult to obtain. Since, for tuning, it is desirable to have the dipole slightly
on the long side, 0.93 was used for K in the length calculations. Spacings between
the. various elements are found with K = 1.
Since this antenna was built and found to be an excellent one, two additional
books have been consulted: "TV and Other Receiving Antennas"8 and the
1952 edition of the "Radio Amateurs' Handbook." The value of K for 5/8" tubing at
77.25 mc. has been checked in each: in the former it turned out to be 0.90; in the
latter, 0.965. This demonstrates just how opinion varies on this matter. Our value
of 0.93 is at least a very good average - and it works. Again, this disagreement
is another excellent argument for the tunable antenna.
The directors should be adjustable from 0.4 to 0.48 wavelength (for 5/8" tubing).
They were, accordingly, made to the dimensions shown - which will allow plenty of
leeway in adjusting the 8" long stubs. Fig. 2 details these stubs. They should
be calibrated in half-inches along their length for precise balancing of the director
lengths on each side of the center boom.
All elements are mounted on the boom through 5/8" holes drilled through the 1"
square tubing. After each element is centered exactly, it is fixed by tightening
the holding screws as shown in Fig. 3. Wooden plugs are fitted into the ends
of all the open tubes to lessen wind resistance.
Fig. 5 illustrates the spacing device for the dipole conductors. The outer
ones are made of aluminum alloy and are used for adjusting the effective length
of the dipole. The inner ones can be made from lucite, bakelite, or red fiber, and
are locked into position very near to the center feedpoint.
Table 1 - Antenna element dimensions computed-for all of the v.h.f.
Fig. 6 shows the center connections of the dipole. A word of explanation
here may be appropriate. Ideally, the feedpoint resistance of the antenna should
equal the surge impedance of the feedline: 300 ohms for 300-ohm line. For many antenna
designs the feedpoint resistance is lower than the line impedance. This mismatch
can be remedied by a commonly recommended device, a quarter-wave, open-end matching
stub. This can be made up of a quarter-wavelength of 300-ohm line attached to the
antenna feedpoint. The 300-ohm line is then attached to the point along the length
of this stub that gives the best match (or best picture). Such a matching stub was
desired on our antenna in case the tuning adjustments for the best picture lowered
the resistance appreciably below 300 ohms. If one tries to picture oneself adjusting
a matching stub of 300-ohm ribbon twin-lead, while experimenting with dipole and
director length adjustments, it will soon be realized that some much more simple
arrangement is desirable. Fig. 10-14 in the 1948 "Handbook" shows that 14"
dia. tubing spaced 1 1/2" apart has a line impedance of 300 ohms. Accordingly, the
300-ohm matching stub was made of 1/4" tubing spaced with Bakelite or Lucite spacers.
For Channel 5 each piece was 35 3/4" long. The length factor K must again be used
and, for 1/4" tubing at 77.25 mc., the 1948 "Handbook" gives this value as 0.945.
Battery clips attached to the feedline can now be adjusted quickly up and down the
stub for optimum positioning.
Fig. 1 shows the completed and adjusted antenna mounted on a 2" diameter
mast 20 feet high. The 1" square boom was mounted in a 1" slot cut into the top
of the pole. It was fastened with a 1/4" carriage bolt and then squared up with
two aluminum shelf brackets of the common variety. The matching stub is not visible
as it was found, after optimum adjustments had been completed, that the best position
of the feedline was the extreme lower end of the stub. This indicated that the antenna
matched the 300-ohm line very closely and thus the stub was not necessary.
Fig. 5 - Details of the dipole spacer units. Four of these
units are required - two of aluminum and two of either Lucite, fiber, or bakelite.
See Fig. 4 for positioning.
Fig. 6 - How the matching stubs are attached to the dipole
of the author's antenna.
A very laborious tuning procedure can be worked out including all the possible
combinations of adjustments if one desires to get the very last ounce of picture
out of this antenna. However, experience has taught that the owners of new television
sets insist on watching the pictures and thus, a shorter and less precise procedure
was, of necessity, followed. Yet, sufficient experimentation was carried out to
insure that almost optimum, if not optimum, results were obtained. Most of the adjustments
were made with the antenna temporarily mounted on the 20-foot mast and the mast
resting on the front lawn leaning against a verandah column. We were able to get
a picture with the array set up in the bungalow's living room and some of the preliminary
adjustments were made there. For each set of director length adjustments, the dipole
length was varied by sliding the outer spacers in and out. Then the battery clips
were adjusted along the length of the matching stub for best results. Observations
were based on picture clarity, contrast (lack of snow in this fringe area during
February), and quality of the audio. The best settings were finally rechecked before
a final setting was made.
After final adjustment, several sets were tried out. It was interesting to watch
the surprised looks of some of the installation technicians when they found they
could not change the picture quality by grasping the lead-in line. We received many
compliments on the installation. Just back of the house is a main thoroughfare,
but buses, transports, etc. do not disturb the picture or the sound. The antenna
bandwidth is good. The test pattern comes through perfectly to the screen with absolute
clarity on all the vertical stripes.
Incidentally, for those who wish to make a Channel 5 antenna without tuning attachments,
the final dipole length was 71", and the lengths of the directors 66", 65", 65"
in respective order of distance from the dipole. These Channel 5 dimensions have
been transposed for the other channels in Table 1. 5/8" If dia. tubing is used for
all channels, but the change in K factor due to changes in the wavelength-diameter
ratio is taken into consideration in the figures. The 1948 "Handbook" does not give
values of K for 5/8" tubing at high-band frequencies. Since we are dealing with
relative values at the different frequencies, we did not worry too much about which
of the other two sources of K values we used. All values for the transposing calculations
were taken from "TV and Other Receiving Antennas."
However, for those who really desire superior results, it is suggested that the
small extra effort put into a tunable antenna is well worthwhile.
1. Smith, Woodrow; "Rhombic Antennas for Television," Radio & Television
News, October, 1949.
2. Morgan, Dean 0.; "Horn Antennas for Television," Electronics, October, 1951.
3. Greenlee, Lyman E.; "High-Gain Directional Array for Marginal TV Reception,"
Radio & Television News, August, 1949.
4. Carmichael, G. N.; "Two-Channel TV Yagi Design," Radio & Television News,
5. Harris, Harold; "The Yagi Antenna," Radio & Television News, October,
6. Shanklin, J. P.; "Bandwidth of Two and Three-Element Yagi Antennas," QST,
7. Dukat, F. M.; "Driven Element Length," QST, October, 1950.
8. Bailey, Arnold B.; "TV and Other Receiving Antennas," John F. Rider Publisher
Inc., pages 318, 319.
Posted August 17, 2022
(updated from original post on 11/25/2015)