When I first saw this article on the 'G-line' transmission system,
I thought the cone at each end of the line was just a gimmick to
make it look high-tech. My ignorance of the way the system works
was responsible. As it turns out, the 'G-line' transmission medium,
named after inventor
Dr. Georg Goubau, an engineer at the renowned U.S. Army Signal
Corps Engineering Laboratories at Fort Monmouth, NJ, used the cone
to transition a finite radius coaxial cable outer conductor to an
infinite radius, sort of virtual,
outer conductor that was free space. Doing so permitted a single
line to do the job of carrying a signal from point A to point B.
This significantly reduced the installation and maintenance cost
of deploying a cable-based communications system - in this case
for television broadcasts in areas where over-the-air- broadcasts
were nearly impossible. G-line came with many of its own unique
issues, and history shows that ultimately it was not a workable
The "G-Line" Community TV System
By Robert B. Gary
Fig. 1 - TV reception by "radiation."
One subscriber merely placed his Yagi near the "G-Line"
and picks up good signals.
The use of a novel transmission line has cut the cost of
system installation and maintenance at Helena, Montana.
The economics of most community TV installations dictate that
the operator bring the TV signal from the antenna to the community
before he can start collecting his installation fees. This means
that the initial investment involves the cost of erecting the antenna
and installing the transmission line and its associated amplifiers.
Maintenance of the system is largely confined to the servicing
of the amplifiers and this item is, therefore, a direct function
of the distance between the antenna and the community. This article
will describe a new method of bringing the signal to the community,
a method which is far more efficient and economical than the conventional
Coaxial cable has an attenuation on the order of 20 db per 1000
feet on the lower TV channels. This means that for sound design
at least two amplifiers are required per mile. In addition to the
initial cost of the amplifiers and their maintenance, in many instances
a special power cable must be strung to these amplifier sites. In
some localities, therefore, consideration was given to a microwave
relay to bring the TV signal from the mountain to the town. FCC
regulations permit public utilities, like A. T. & T., to lease
their microwave facilities to community TV systems but forbid the
community operator installing his own microwave link. As a result,
many community TV installations remain paper projects.
Television reception is not possible in Helena, Montana, but
only 15 miles away is McDonald Pass and the Continental Divide,
and channel 13 can be picked up there from Missoula. By conventional
coaxial cable methods the 15-mile haul would cost $40,000 to $50,000
just for the initial installation.
Helena was fortunate in having Bruce Hamilton, an alert engineer,
in charge of its community TV project. He had read about the "G-Line"
and realized that this technique might solve Helena's transmission
problem. After some study and investigation, Mr. Hamilton started
on the project of installing the first "G-Line" in a community TV
Fig. 2. The "installation" of the "G-Line"
consists. for the most part. in suspending the line from
the cross-arm of a utility pole by a quarter-inch nylon
Fig. 3. One of the "launchers" used in
the Helena installation.
Fig. 4. Nine horns and amplifiers cover
the 15-mile stretch.
The "G-Line" is named after its inventor, Dr. Georg Goubau, who
developed this single-wire line for the U.S. Signal Corps. (Details
on this line were given in Leonard Lieberman's article, "The G-Line
Antenna Lead-In," in the April 1955 issue of this magazine). Fundamentally,
the characteristics of this line are those of a coaxial cable of
fixed dielectric except that the outer conductor is placed at infinity.
By choosing the proper relationship between the inner conductor
and the surrounding dielectric diameter, the mode of wave propagation
is largely axial. It is only necessary that the single-wire line
be fed from a coaxial system by means of a carefully designed "launcher."
This is, effectively, a cone with the center conductor at its apex
and the outer conductor making the transition from the coaxial cable
to the infinite spacing.
Fig. 3 shows a typical "launcher" as used in the Helena installation.
The "G-Line" has some remarkable properties. Its losses at the lower
TV channels are on the order of 10 to 20 db per mile depending on
the particular installation. The installation of the single-wire
line is slightly tricky. When the line is about a half wavelength
from the pole or other object, the loss at that point will be 0.05
db. Losses due to bends in the line become appreciable as the corner
is made sharper. Theoretically, the db losses vary with the square
of the bending angle and whenever bends are required they must be
as gradual as possible. Another important characteristic of "G-Line"
is that, theoretically, there is very little radiation. In actual
practice Mr. Hamilton found that the radiation from the single-wire
line was a maximum of 1.5 microvolts-per-meter at a distance of
ten feet and this was at a point of greatest signal energy level.
This factor is confirmed by the photograph of Fig. 1, which shows
a rather unique method of tapping off a TV line: A home owner along
the route of the "G-Line" simply placed his yagi antenna close to
the wire and got good TV reception. This method "has the operator's
sanction since the regular rental fee is paid by this "radiation
The channel 13 signal from Missoula is received by a conventional
antenna array and amplified before it is converted down to channel
4. This conversion was suggested by the poor performance of the
channel 13 strip amplifiers which were tried first. The "G-Line"
itself is more efficient at the higher frequencies but the amplifier
considerations outweighed this feature. For channel 4 transmission,
the maximum diameter of the "launcher" is 58 inches with a taper
angle of 45 degrees. The inner conductor of the "G-Line" is #8 Copperweld
and the dielectric is brown pigmented polyethylene with an outer
diameter of 0.253 inch.
Although the theoretical distance from foreign bodies should
be on the order of half a wavelength, for practical reasons the
wire was suspended about 15 inches below the lowest cross-arm of
the telephone poles belonging to the Mountain States Telephone trunk
line. In most straight sections the line is suspended by 1/4-inch
nylon rope as shown in Fig. 2. At some bends 15-inch polystyrene
rods are used to brace the line horizontally. The telephone poles
from McDonald Pass (altitude 6000 feet) to Helena (3000 feet) predate
the road and therefore run along the road at only a few points.
Distances between poles vary and the line crosses the new U.S. Highway
10 several times. Because power is not readily available at all
points along the line, the line amplifiers are located at unequal
intervals and the longest stretch of "G-line" is about 2.5 miles
between amplifiers. On that stretch the total losses over 2.5 miles
are only 53 db.
A total of nine line amplifiers is required to cover the 15-mile
stretch. Mr. Hamilton found it necessary to space the receiving
and transmitting launchers about 120-feet apart at the amplifier
stations in order to avoid ghosts caused by feedback. Recent Signal
Corps tests seem to indicate that "launchers" can be placed back-to-back
without appreciable separation and it may well be that some mismatch
exists in the Helena system which causes this feedback problem.
A typical horn and associated amplifier are shown in Fig. 4, and
it is clearly apparent that the output of the "launcher" apex goes
through the RG-11/U to the conventional line amplifier.
In Helena, the signal is distributed to over 500 homes by means
of RG-11/U, double-shielded coaxial cable and conventional distribution
amplifiers. A total of 70 miles of RG-11/U has been used to date
in Helena just to hook up subscribers to the distribution amplifiers.
The installation fee is $125.00 with a monthly tariff of $3.75.
The major initial investment, as in all community TV projects, was
the cost of bringing the signal down from McDonald Pass. While conventional
coaxial cable and amplifiers would have cost at least $40,000, the
actual cost of installing the 15 miles of "G-Line," including the
price of the wire itself, the amplifiers, antennas, power connections,
etc., was only slightly over $12,000.
The weather conditions at the Continental Divide are probably
the most severe, with regards to snow and ice, in the country. During
the past winter, however, the signal was lost for only half an hour
when an inch of wet snow accumulated on large portions of the line.
As soon as the snow had melted or fallen off, the signal was restored.
Since there is no outer conductor, the problem of moisture seeping
in or condensing between the outer conductor and the dielectric
does not exist. The outer polyethylene jacket has, in other applications,
proven to be almost impervious to weathering for a considerable
Helena TV Inc., the operator of this pioneer "G-Line" community
TV system, is licensed by Surface Conduction Inc. of 521 Fifth Avenue,
New York, the company which holds all commercial rights to Dr. Goubau's
patents. So successful is the Helena installation that its owners
are now intent on tackling a 27-mile line in the area.
Other community TV systems which are planning to use the "G-Line"
include the Neighborhood TV Corp. of Owen Sound, Ontario. Here the
TV signal will be received at a suitable high point as close to
Toronto (150 miles away) as possible and then transmitted to Owen
Sound along the telegraph poles of the Canadian Pacific Railroad.
The most recent application of the "G-Line" to community TV was
in September 1956 when an "open wire" transmission line was replaced
by a single wire "G-Line" extending over 8000 feet in the Port Jervis
community TV system. Port Video Corporation, owners of this system,
found that this changeover resulted in improved performance.
This new "G-Line" installation extends (apart from poles belonging
to General Telephone and Rockland Light and Power), over system-owned
poles separated by 600 feet or more, thus showing the adaptability
of the line to varied local conditions.
Posted April 13, 2015