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 (reject)
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 magazine was
written by a serviceman who troubleshot and solved many of the issues prevalent
in his day - a very interesting read.
More About "Man-Made" Static
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.
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.
But consider a number of these appliances used at alternate intervals, and we
have a chain of interference that will last for hours.
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.
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.
Fig. 3 - We may see how many opportunities for a loose contact
are afforded in a meter installation: Count the Xs.
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.
Fig. 5 - A filter for telegraph interference.
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.)
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 canopy.
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
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.
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.
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.
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.
Posted June 29, 2022
(updated from original post on