August 1947 Radio News
Wax nostalgic about and learn from the history of early electronics.
See articles from Radio &
Television News, published 1919 - 1959. All copyrights hereby acknowledged.
Most of us here in America recognize the Packard Bell name from
the line of personal computers (PCs) they sold in the 1980s and
1990s. I owned three of them, beginning with an Intel 80286 model,
then an 80486, and finally a Pentium model. They were in the 'pizza
box' format that sat on the desk with the CRT monitor on top; I
always preferred that configuration over the tower type.
Before Packard Bell made personal computers, they made personal
desktop beginning back in the 1930s. That explains why Mr.
J.T. Goode, an engineer with Packard Bell, would write an article
in 1947 regarding a method to tune antennas using light bulbs. His
example is for the 10-meter amateur radio band at 28.00 MHz
to 29.69 MHz. If you do not have a SWR meter and are confident
that the antenna and transmission line feeder are pretty close to
spec, then this method serves as a good way to fine tune the antenna.
Although not explicitly mentioned in the text, I assume that judging
the relative brightness of the bulbs, especially since they are
located on the antenna elements, requires performing the procedure
in low ambient light level conditions, like at night.
Packard Bell was sold to a European company in the year 2000,
and now markets PCs in the EU and Africa.
Antenna Loading Problems and Solutions
By J. T. Goode
Asst. Chief Eng. Packard-Bell Co.
panel light bulbs are the only pieces of equipment required to properly
match antenna to transmitter.
Anyone who loads a transmitting antenna for the first time soon
finds out there is considerably more to the problem than what appears
on the surface. The necessity of a proper match for transferring
electrical power is a well established fact. Ways and means of accomplishing
this result are numerous. To the engineer holding a college degree,
the problem is purely mathematical. To the newcomer in radio, the
problem is normally solved by an infinite number of experiments
which result in a questionable answer. This same type of answer
may be experienced by the engineer if he relies wholly on mathematics
to create the proper match.
When a transmitter is correctly matched to an antenna, the mathematical
solution is achieved. Mathematical solutions to such problems deal
with all circuits in a perfect state, which is seldom possible.
Such being the case, the engineer must be in a position to decide
where a compromise can be made in the effort to obtain perfection.
The purpose of this article is to show short cuts with various r.f.
Many different types of low impedance transmission lines are
now available. The first thing to keep in mind is that the proper
impedance transmission line is required for different types of antennas.
For instance, a folded dipole type antenna requires a 300-ohm transmission
line for proper termination. The proper transmission line for a
doublet antenna is 72 ohms.
Assuming that the proper impedance transmission line has been selected
for a particular antenna, the next step would be proper termination
at the transmitter end. Commercially constructed pickup coils are
now available with a known impedance. If such a coil is not used,
the correct number of turns can be established by experimentation.
Fig. 1. Pilot lights used to match doublet antenna (A)
and off-center Hertz antenna (B)
Assuming the antenna is erected and the transmission line terminated
on both ends to the best of your ability, the next move will be
to make final adjustments and to determine that the adjustments
are giving a maximum transfer of power from the transmitter to the
Proper termination on the antenna end of the transmission line
can only be obtained when the antenna length is a half wavelength
at that particular frequency. When the transmitter frequency is
shifted above or below this center point, a noticeable decrease
in transmitter load will result. Antennas naturally take a maximum
load at one frequency, so as the frequency is changed two things
cause the antenna loading properties to decrease - mismatch of the
transmission line and incorrect antenna length for the particular
Although there are many methods of making final adjustments on
an antenna, the author selects the following for reasons that can
be readily understood, namely, economy and accuracy with a minimum
amount of time and effort.
The use of two sensitive r.f. microammeters is perfectly satisfactory
for the following adjustments, but the meters require identical
calibration. These meters are expensive and may be easily damaged
with overloads. There is another r.f. indicator which, for this
particular application, is equally as accurate as r.f. microammeters
and costs 5¢ per indicator. The common panel light bulb meets
this requirement. In case of an overload the expense of the damage
will be the price of a light bulb.
Installation of R.F. Indicators
For example, let us assume that we are working with a transmitter
with an input of 100 watts, and a frequency of 10 meters.
Two wires are soldered to the connections of the light bulb base.
These wires should be approximately six inches long. Two such light
bulb assemblies are required. Refer to Fig. 1A for proper connection
of light bulb assemblies to the antenna.
Load the transmitter antenna by adjusting the pickup coil to
the tank circuit of the final. Note brilliancy of light bulbs. Adjust
antenna length for maximum brilliancy in each light. When this adjustment
is correct, both light bulbs will be equal and at maximum brilliancy,
indicating a maximum transfer of power from the transmitter to the
antenna. If the impedance of the transmitter pickup coil is unknown,
vary the number of turns so that maximum brilliancy of the light
An antenna tuned by this procedure provides a maximum transfer of
power from the transmitter to the antenna, which means that the
best possible match for the particular application has been achieved.
Under such conditions, the standing wave ratio on the transmission
line is at a minimum. If such a condition does exist, the addition
or subtraction of transmission line to the particular circuit will
not affect the amount of power being transferred to the antenna
other than the actual loss in the transmission line. Another method
of indicating standing waves on a transmission line is to apply
water to the transmission line and observe any change in the transmitter
loading. A 72-ohm Amphenol flat transmission line is relatively
unaffected during a rainy season if the line is free of standing
Placing r.f. ammeters in series with the transmission line will
not give an accurate indication of maximum transfer of power to
the antenna. A standing wave on the transmission line can cause
excessive current to flow which would be indicated by the ammeter
with a very small percentage of this power actually going into the
antenna. If such a condition does exist, the loading of the transmitter
can vary radically during a rainy season.
It is possible to have a standing wave on a transmission line
and still load the antenna with a fair degree of success. Such a
condition exists when an untuned transmission line is cut to length
resulting in optimum operating conditions.
The number of amateurs that cut transmission line to obtain the
proper transmitter load is surprising.
If the light bulbs exceed their normal brilliancy during the
tuning operation the length of wire to each bulb should be reduced
equally. The light bulbs will then shunt a smaller portion of the
antenna, resulting in less voltage being developed which reduces
For tuning applications, using low-powered transmitters, it may
become necessary to use low current drain panel lights and shunt
as much as 18" of the antenna. A 1-kilowatt transmitter will require
approximately 4" of lead length for normal brilliancy.
The light bulb method of tuning antennas can be adapted to practically
any antenna. To prune an off-center-fed Hertz antenna, the following
procedure should be used:
Three lights bulbs are required, one at the center of the antenna,
and two light bulbs shunting portions of the feeder. These two light
bulbs on the feeder should be spaced approximately 10' apart. Refer
to Fig. 1B.
The antenna is connected to the transmitter and the transmitter
turned on. The antenna length is then adjusted so that the light
bulb in the center is at maximum brilliancy. The next adjustment
is to slide the antenna feeder to different positions on the antenna
so that both light bulbs on the feeder have the same brilliancy.
If the light bulb on the antenna is at maximum brilliancy and the
two light bulbs on the feeder are equal; the feeder is a non-resonant
transmission line and the antenna is cut to the proper length.
A final check is made by moving one of the feeder light bulbs
approximately 4'. After this adjustment has been made, the two feeder
light bulbs should remain equal in brilliancy. If there is a difference
in brilliancy, the feeder will require additional adjustment at
Although the light bulbs make fine power output indicators as
well as modulation indicators, it is recommended that they be removed
after all adjustments have been made. If the neighbor's radio jumps
off the table and these light bulbs light up at the same time, the
neighbors undoubtedly will conclude that your transmitter had something
to do with their particular problems.
Posted October 13, 2014