May 1930 Radio-Craft
Wax nostalgic about and learn from the history of early electronics.
See articles from Radio-Craft,
published 1929 - 1953. All copyrights are hereby acknowledged.
Manmade electrical noise (QRM)
and natural electrical noise (QRN)
has been the nemesis of communications - both wired and wireless
- since the first signals were sent. While it is true that over
the last century the amount of 'background' noise has increased
significantly, the ability of modern circuits to deal with
it and/or accommodate (error
correction) it has pretty much kept up with the advancement.
You might be tempted to think that 'back in the good old days'
such problems did not exist, but operators were plagued by poorly
designed and inadequately filtered transmitters as well as really
deficient electrical service installation that spewed noise
from transformers, inadequately grounded transmission lines,
lousy connections, and arcing motor brushes. This 1930 article
from Radio-Craft was written by a serviceman who troubleshot
and solved many of the issues prevalent in his day - a very
More About "Man-Made" Static
A Trouble-Shooter tells of some sources of interference which
he has found in his regular work of checking radio noises
By J. E. Deines, W9CU
Much has been said about electrical apparatus that interferes
with radio reception, about methods of location, the kind of
set to use in this work, and all that - but still there is that
puzzling case that makes you scratch your head and wonder what
it is all about. Perhaps some of these ideas will help you.
We all agree that the noise travels back on the electric
line, much in the manner of "wired radio"; and that the way
to look for it is to keep the loop parallel and directly under
the line, then reduce the volume and try - first in one direction
and then the other - until the loudest spot is found. This is
usually a pole. If it is secondary distribution that you are
working on, the trouble is probably in some one's home. There
are two things that you can do in this case. Either walk under
the "services" (lighting lead-ins to houses) one at a time,
and pick the loudest; or ask everyone connected to that pole
what they are using and, if it sounds suspicious, have them
shut it off to prove your case.
In this day and age of powerful and sensitive receivers,
interference seems to be on the increase. A check of the electric
light companies' records shows that about 65% of the trouble
located is in consumer's appliances; while the owners of these
do not seem to realize the importance of applying filters, and
usually make the statement that they use the appliances only
for a few minutes.
Fig. 1 - The high-voltage lines, which in
some systems are used for "wired wireless" distributors, also
carry unwanted R.F. noises from one house line to another, sometimes
a long ways off - as from No. 1 to No. 3 here.
But consider a number of these appliances used at alternate
intervals, and we have a chain of interference that will last
Radio has a peculiar place in the electrical industry, due
to its rapid growth in the last ten years. It has grown to a
giant ranking next to the automobile, and we have only. "scratched
the surface." Too much time has been spent selling radio and
not enough spent in making a place in which to use it.
We are now facing the problem of working over and filtering
all our old equipment (which is, otherwise, operating normally)
to make the world, speaking from a radio standpoint, a better
place in which to live.
Some noises which can be heard on the electric sets can not
be heard on the trouble shooter's set, even under the house
"service"; - that is, interference which is not a major noise,
that would spoil reception entirely, can be heard on a sensitive
A.C.-operated set when a station is tuned in. It creates a background
roar and spoils the tone quality. The reason for this is that
the electric set is more closely coupled to the line than the
portable; and a careful inspection of the electric lines in
the vicinity will soon get you on the right track. It can readily
be seen from Fig. 1 that interference set up in one secondary
line will in turn set up an interference in a parallel line;
the intensity of the transfer depending on the length of exposure.
The noise will be weaker, to be sure; but nevertheless it is
there and can be found if looked for in the proper manner.
Troubles in House Wiring
We all know that any arc or spark causes radio interference,
and we can no longer tolerate loose connections. An easy way
to find troubles from this source in house wiring is to turn
on the radio set at full volume, shake all fixtures and pound
all the wall switches, listening for cracks and pops that you
will no doubt hear. Many of the older houses throughout the
country were once piped for gas lights and, in some cases, combination
gas and electric fixtures are still in use. Others have the
pipes capped off under the new light and fixtures. Here is a
place for a lot of trouble. In an installation of this kind
it is very seldom that the fixture is free from grounds. (See
Fig. 2 - One side of an A.C. line is grounded;
if a fuse in this line blows, a ground in the wiring will cause
all kinds of radio disturbance.
When lightning strikes in the vicinity of the electric line,
the induced current usually runs into the house and jumps off
at the most likely spot - the gas-pipe ground - and the result
is damaged insulation. If it is on the live side a fuse goes
out; but, if it is on the ground side of the line, nothing happens
until the fuse (X) goes out. Then the fun begins. The current
flow is now from X to the transformer ground in the alley and,
because contact is poor in the fixture, an arc is the result.
Several cases of this kind were found where a loud buzz was
set up with the set turned on only about sixty watts. The greater
the load, the louder the buzz.
It seems to be a habit with the electricians, when they cannot
find a ground in the wiring, to reverse the circuit; thus putting
the grounded wire on the neutral or ground side of the electric
line. This is all right where there are no neutral fuses but,
if there happens to be one and it blows, then the noise starts.
Therefore, if in doubt as to the origin of the noise look at
the neutral fuse.
In a fixture of the type shown in Fig. 2, where the wire
is woven through the chain, a static charge is set up in this
chain and, as long as everything is quiet, there is no trouble.
But walk across the floor, or otherwise move or jar the chain,
and a crackling or popping noise will be set up. The cure here
is to tape the eyelet (Z) and thus insulate the chain from the
Another spot in house wiring that will bear watching is the
entrance switch at the meter; here is a likely place for loose
connections. (Fig. 3). All places marked X are likely places
and, if the meter switch and fuse box happen to be located near
a door, the vibration due to constant opening and closing of
the door will loosen all screws and fuses. These loose connections
can be found by the method used above.
Fig. 3 - We may see how many opportunities
for a loose contact are afforded in a meter installation: Count
Even the lowly electric lamp comes in for its share of the
blame. Investigation of one complaint showed that the noise
was coming from a neighbor's home; but only a 100-watt lamp
was turned on that time. Turning it off stopped the noise, and
it was found that the lamp filament had parted and was holding
an arc that did not go out until the lamp was turned off.
Troubles in Receivers
One day we received a complaint of a humming noise which
came in at one spot on the dial. During the course of the evening
it would move from place to place. Upon investigation it was
found that a neighbor was using a superheterodyne he had built
from a kit. By a mistake in wiring, the antenna was coupled
to the oscillator, and it would radiate at double the frequency
the set was tuned to.
The heater-type tube causes a number of complaints, for it
sometimes emits noises that imitate most any interference. All
are caused by a static discharge from heater to cathode. Many
sets are found with defective power packs. Small arcs in the
condensers, due to loose connections or high-resistance short
circuits, cause many of the unusual growls heard in the listener's
sets. Also some voltage-divider resistance units have a broken
wire caused either by corrosion or by breakage due to contraction
or expansion. This will show up only when the set gets good
and warm; and many other complaints of this type, that appear
after the set has been for use for hours, will account for the
large number of cases found clear at the time of inspection.
Fig. 4 - A bad ground furnishes a coupling
for line noises, even though there is a filter in the input
of the set. The reason may be seen above.
Strict attention should be paid to the ground wire and its
connections. When it· is connected to the antenna post trouble
starts. With such a connection, the light line acts as an antenna
and, since interference travels on the line, we can readily
see what will happen. In districts where street cars are used
or direct-current lines exist such connection makes the noise
about 30% louder.
It always pays to put up a good antenna.
Loose connections in ground wires always cause trouble; because
any number of electric receivers use by-pass condensers on the
line side of the power transformer. Since even a small condenser
will pass alternating current, and since the electric company's
lines have a grounded center or neutral wire, a small arc will
result at the point of poor connection. (Fig. 4.)
Another condition that will produce a loud hum is a lamp
sitting on top of the set over the detector tube or cord stuffed
inside the set too near the tube.
Fig. 5 - A filter for telegraph interference.
Key click from telegraph offices some times causes severe
interference in the form of a loud popping or thumping noise
and, when other lines parallel the circuit, it will spread over
a large area. This is not so hard to find, but the cure may
be a little harder. Use a 1/2-mf. condenser with about 200 ohms
in series across the key. The resistance should be variable,
and different sizes of condensers may be tried until the noise
is stopped and the key does not arc too much at the contact.
One piece of electrical apparatus emits a noise that sounds
like the ticking of a clock; it is licensed under the Abrams
patents and used for electrical treatments. The same filter
will apply to this.
The trouble shooter's life is not all roses. He is usually
a much cussed and discussed man and, if every owner of an interfering
device would apply a filter, it would save him many a gray hair
and many a cold ride.
The writer of this article embodies in it
a good many hints that will be found of value by the Service
Man who has to deal with those mysterious noises that cause
so many calls.
Posted August 27, 2015