June 1934 Radio-Craft
[Table of Contents]
People old and young enjoy waxing nostalgic about and learning some of the history of early electronics.
Radio-Craft was published from 1929 through 1953. All copyrights are hereby acknowledged. See all articles
The effort to block advertising on radio broadcasts has been
going on for about as long as advertising has been in use, as
evidenced by this 1934 article in Radio-Craft where
a 'robot' advertising silencer' device is presented for removing
'superfluous advertising.' Headlines from a few weeks ago announced
Apple's program for
blocking ads that appear on websites, causing a big to-do
about how all the 'free' content would be jeopardized since
it is the advertisers who pay for the music and other programming
to be delivered to the user. Without the convenience and economy
of software to do the job in 1934, however, fairly complex discriminator
circuits were used to detect and mute the 'garrulous announcer
or advertiser' between regular programming. It's pretty funny
to read about how annoyed people were with the advertisements
- just like today.
I hate the ads that automatically play audio rather than
providing an option to listen. Besides, those video and audio
ads consume a lot of bandwidth when downloading, so that delays
the website content from loading as quickly as it could otherwise.
Most of my radio listening is via the Internet, and of course
those broadcasts are chock full of advertisements. There is
an option to pay a monthly subscription to avoid the ads, but
they don't offend me quite that much ;-)
An Automatic Program Sensor
Radio-Craft, in the March, 1934 issue, was the first to announce
a radio "robot" that automatically silences superfluous advertising.
While this invention may never be put to use as an advertising
"silencer," it may suggest some other equally practical application.
No longer will it be necessary to endure half an evening
hearing detailed advertisements on tombstones, dog biscuits,
soap or "laughing water" in order to spend the remaining half
enjoying entertainment. Geo. P. Adair, an electrical engineer,
has just invented a novel device that seems almost human in
its discriminatory powers to regulate an incoming radio program.
It automatically cuts off the garrulous announcer or advertiser
who sandwiches an "ad" between every note of music or tactlessly
carries his advertising speeches to the point of nausea. This
special receiver makes it possible for the radio audience to
take as much or as little of advertising as they please, or
to have an uninterrupted musical program if they so desire.
Of course, like many other inventions this one may never
be put to wide practical use. In the first place, the people
of the United States are well aware that the advertiser is the
one who pays for the notwithstanding immeasurable pleasure afforded
them by radio. Far more fortunate are Americans than the people
of European countries where tax is levied on individual radio
equipment. In Germany, for example, the postman collects a radio
tax at regular intervals that is set by the government.
Fig. 1 - Circuit diagram illustrating arrangement
of a radio receiving set embodying a means of discriminating
between music and blatant advertising. See text for complete
And so that automatic "censor," just patented by its inventor
George P. Adair, is explained to us not as a means to annihilate
advertising, but rather as a restraint to be used when necessary.
Or, as John B. Brady, attorney for Mr. Adair, aptly put it,
to eliminate advertising would be to kill the goose that lays
the golden egg for broadcasters.
Fig. 2 - Automatic switching arrangement
from receiver to phonograph when lengthy talks begin.
It is quite satisfying to our romantic conception of the
development of an invention to know that the material used principally
in the construction consisted of a baby bed, a wastepaper basket,
coffee and baking powder cans, pie and cake pans and other discarded
articles assembled by the inventor. Mr. Adair has built a number
of these radio sets which operate splendidly.
Broadly speaking the invention relates to radio reception
and particularly to a special circuit arrangement for radio
broadcast receivers. Mr. Adair arrived at his conclusions and
subsequent invention by basing it on the fact that the characteristics
of the speaking voice are different from those of vocal and
instrumental music. Except in very unusual cases there are few
definite pauses in the latter, while in the speaking voice there
are numerous and quite definite pauses between syllables and
words, and quite long pauses between phrases and sentences.
If the electric waves caused by speech are rectified, the current
resulting is of a pulsating nature, while in the case of music
it is a direct current that varies little in amplitude.
Fig. 3 - A method of censoring advertising
by automatically switching on another program.
The receiving apparatus serves in various ways. A circuit
arrangement may be fixed so that silence replaces the extended
advertising talk, and nothing is heard until the music is again
begun. By operating another switch, the device automatically
works so that it simply changes over to another station when
music is discontinued on one, thereby obtaining a constant musical
program. Or again an arrangement may be employed whereby the
sound-reproducing system is switched to an automatic phonograph
or other form of automatic recording device, which will permit
the reproduction of a desired record between the musical broadcasts.
As soon as musical or vocal selections are again being broadcast
the receiver automatically responds again to the radio broadcast.
If it is desired to render the speech-eliminating system inoperative,
or in other words to have the set perform as a normal radio
broadcast receiver, one simply closes a designated switch.
The system of this special receiving arrangement, in detail,
is as follows: You may note by Fig. 1, that there is a receiving
circuit connected to an input-circuit including primary winding
3 of the coupling transformer 4. Secondary winding 5 of coupling
transformer 4 is tuned by variable condenser 6. In turn, the
tuned circuit connects to the input system of an R.F. amplifier
including electron tubes 7, 8 and 9. At this point the detector
tube 10 connects to the output circuit of the R.F. amplifier
system. The tuning elements 6, 11, 12 and 13 for the R.F. stages
and the detector stage of the receiving arrangement are at the
same time controlled as shown through dotted line 14. The output
circuit of the detector tube 10 connects to the A.F. amplifier
system made up by electron tubes 15 and 16 connected in parallel
for obtaining greater power output. The output circuit of the
A.F. amplifier stages 15-16 includes transformer 17, the primary
of which is shown at 18 connected to the output circuit of tubes
15 and 16 through the coupling condenser 57; and the secondary
winding of which is indicated at 19 joined to the sound reproducer
marked at 20. Coil 21 of the electro-dynamic speaker system
composing the loudspeaker 20 is movable and is connected in
series with contact 22 of a relay at 23. The field winding of
the reproducer 20 is shown at 24 suitably energized from the
output circuit of the detector tube 10 as shown at 26. This
path leads to auxiliary control tube 27. A selective filter
coupling device provides the input circuit of tube 27. A resistor
31 completes the input circuit to the auxiliary tube 27. Grid
27c, of control tube 27, is normally biased to a negative potential
of such value that the tube works on or below the lower knee
of the characteristic grid-voltage, plate-current curve. Resistor
31 provides this negative potential, and is connected to the
ground which is maintained at a negative potential in relation
to cathode 27a through the voltage drop caused by a current
flow through resistor 48. The circuit of the latter is completed
through resistor 50 and conductor 34 to the power supply. Condenser
51 serves as a smoothing unit. Output of control tube 27 leads
from the anode 27b to the electro-magnetic helix 32 forming
part of a relay. The circuit of 32 is completed with a resistance
33 which goes through at 34 to the power supply circuit. The
relay 32 controls the armature tongue 37 which moves with relation
to contacts 38 and 39. A vacuum tube relay at 41 has an input
circuit passing through the conductor at 42, which connects
to tongue 37 of the relay. When the armature moves against contact
39, increased negative potential is placed on the grid 41c of
tube 41. This is caused by a negative charge which collects
on the grid condenser indicated at 47 through resistance 40
and connection to ground which is normally kept at negative
potential with respect to cathode 41a through resistance 48.
When the negative charges are placed on the grid, it results
in decreasing the plate current in the output circuit. The latter
is completed through resistance 33 to the path of positive plate
potential through conductor 34. If the armature tongue 37 is
held contacting 39 a given period depending on the resistance
and capacitance and the operating constants of the tube used,
the negative biasing potential increases until the plate current
is decreased to a low value which in turn de-energizes the relay.
The relay contacts are thus closed, finishing the circuit through
the voice-coil 20 of the dynamic loudspeaker. The device is
now ready to receive vocal or instrumental music. When the armature
tongue is contacting, the charge will be reduced by leakage
through resistance 45 until the potential on the grid will allow
enough current to flow in the output circuit to energize relay
23 and to open the circuit to the voice-coil of the loudspeaker
making it inactive.
When the phonograph is to fill in musical lapses, a system
is used, Fig. 2, that switches the A.F. amplifier portion of
the broadcast receiver to the control portion of a recorder
circuit by which recorded programs are reproduced electrically.
To do this an auxiliary unit is coupled to the output circuit
of the R.F. amplifier stage and connected to a relay control
system. The latter connects the phonograph actuating circuit
into the input of the detector tube for using the detector tube
as part of the A.F. amplifier system, This includes the R.F.
detector stage which is coupled through a conductor and coupling
condenser to the output of the R.F. amplifier. The other side
of the input circuit to the detector stage is finished by the
impedance circuit to the ground. The output of the detector
stage is coupled through the coupling circuit with the input
circuit of the A.F. corrective tube. A filter circuit is used
between the output circuit of the R.F. detector and the input
circuit of the subsidiary detector tube. In other words, filter
elements at three points are arranged in the circuit with the
A.F. rectifier tube to differentiate the range of voice frequencies
and the range at musical frequencies to which the detector responds.
When the relay is energized due to lengthy speaking or cessation
of music, contacts close which in turn cut off the circuit to
the driving motor and start the twitch of the automatic phonograph.
In cases when it is desired only to eliminate extended speech
and not to substitute any other program, this is accomplished
by opening the circuit to the loudspeaker. This and the other
previously mentioned ways in which the receiver serves is done
merely by opening of the various switches. A- multi-point switch
operated by a single control may be used for these various switching
A system for substituting other radio programs for those
in which undesirable speech predominates is shown in Fig. 3.
The speech and music wave-form difference upon which all
these systems depend for their operation is immediately apparent
to those who can diagnose the graph shown in Fig. 4.
The differences belween speech and music in wave form are
clearly shown by the curves above. It will be noted that there
are open spots in the speech curves, which permit the censor
Posted October 21, 2015