US1949848A - Radioreceiver - Google Patents

Description

E. D. TILLYER RADIORECEIVER March 6, 1934.

Filed Aug. 4, 1950 Patented Mar. 6, 1934 UNITED STATES RADIORECEIVER Edgar D. Tillyer, Southbridge, Mass assignor to Radio Corporation of America, New York, N. Y., a corporation of Delaware Application August 4,

2 Claims.

This relates to radio receivers and has particular reference to means for improving the quality of reception.

The principal object is to supply means for automatically controlling the volume of sound reproduced by a radio receiver.

Another object is to maintain the reception of radio signals at a desired strength without fluctuation.

Another object is to provide means whereby the fluctuation in the strength of reception of radio signals can be eliminated without afiecting the quality of the signals received.

Another object is to provide simple and efficient means to obtain the advantages of the invention.

Other objects and advantages of the invention will become apparent from the following description taken in connection with the accompanying drawing, and it will be apparent that many changes may be made in the details of construction and arrangement of parts without departing from the spirit of the invention as expressed in the accompanying claims. I, therefore, do not wish to be limited to the exact details of construction and arrangements shown and described as the preferred form only has been shown by way of illustration.

The single figure is a diagrammatic view of a typical radio receiver embodying the invention.

It is well known that all music, speech, etc. reproduced by a radio receiving apparatus is subject to fluctuation in volume, which is due to the effects of a hitherto uncontrollable cause known as fading." If the radio receiving set is adjusted to give a desired volume it is seldom that the level can be maintained for any length of time. Usually when fading occurs the receiving set must be adjusted to bring the signals in louder and readjusted when the fading disappears and the original volume is restored. It is obvious that some provision should be made to eliminate the effects of fading on the strength of the signals heard. The continual adjusting now necessary is a very bad feature of the present day radio receiving apparatus. This invention, therefore, is concerned with a novel solution of the major faults of radio receivers and to provide simple means for increasing their efiiciency.

Referring to the drawing there is shown a typical radio frequency amplifier 1 conventionally shown which may be tuned to the frequency of the incoming wave. The amplifier 1 may be of the well known neutralized type or any simi- 1930, Serial No. 473,084

(Cl. fem-20) lar circuit. The numeral 1 may'also designate the signal frequency amplifier and local oscillator preceding the first detector, as in the superheterodyne thus giving a wide scope for the use of this invention. The output of the radio frequency amplifier 1 is coupled in the usual way to a detector stage 2 which for the purposes of this description may contain coupling coils 3 and a variable tuning condenser 4. The usual grid condenser 5 is connected in the grid circuit of the detector tube containing the grid 7, the plate 8 and the filament or cathode 9.

The grid leak 6 permits the grid charges to leak off. The detector plate circuit is coupled, by the usual audio frequency transformer 10, to any well known type of audio-frequency circuit. This invention is not directly concerned with the audio frequency circuit of radio receivers, a description of the same is accordingly omitted as being superfluous. A bypass condenser 11 is shunted across the primary of transformer 10 arranged in the circuit of plate 8, the latter being connected to the positive terminal of the B battery. A preferable circuit arrangement to obtain the advantages of the invention is shown in the lower part of the figure, and it will be seen to be of simple and inexpensive construction.

From the grid circuit of the detector tube, and connected between the variable condenser 4 and the grid condenser 5, there is preferably connected a rectifier, as a crystal detector 12. It is to be understood that any type of rectifier, as a tube detector or rectifier could also be used without detriment to the proper functioning of the apparatus. In series with the detector or rectifier 12 which rectifies the incoming wave, there is connected an audio frequency choke 13. This is constructed with an iron core and has a large inductance, and is similar to that used for very low frequencies. Instead of the iron core audio frequency choke I may use a high resistance which will give the same desired efiect. This portion of the circuit passes radio frequencies freely. The choke 13 is adjustably connected to a potentiometer 15 which controls the bias from the E battery. An ordinary A battery is connected to the filament circuit 9 in the usual way and a B battery through the plate circuit. A fixed condenser 14 is connected across the choke 13. This fixed condenser 14 may be omitted if the choke value is large enough to take care of the incoming current, but if a small choke is used it will be necessary to introduce the fixed condenser 14 across the small choke.

In the operation of the radio receiving apparatus incorporating the present invention the station desired is selected by tuning in the usual way by means of the variable condensers in the radio frequency and detector circuits. The strength of the signals is adjusted and the set can be left until fading occurs. The desirability of this invention now becomes apparent. By means of the potentiometer 15 the power from the E battery increases the strength to any desired amount and the weakness due to fading is entirely eliminated. Now when the fading effects disappear the volume of the original signals will be restored and in an ordinary set a new adjustment would be necessary. .With this invention incorporated in the radio frequency circuit of a receiving apparatus the excess cur-.

forte will be maintained for the simple reason that the whole volume of a voice may be raised or lowered in strength without affecting the variation in strength between the individual notes.

As an illustration of the novelty and simplicity of the invention we may imagine a maximum average signal of three volts being received at the radio frequency amplifier. This is rectified at three volts by the crystal 12. If the bias is just suflicient to prevent the passage of three volts then no damping will occur. We can imagine that the power required for audible signals at the peak of "fading is three volts. When the fading effects disappear we may get an increase of signals to four volts which would be much louder than required if allowed to pass to the reproducing apparatus. However, as the bias from the E battery is 'sumcient to prevent the passage of a three volt current then the extra volt will be .eiiectively passed to dampen the circuit. A charge builds up in the distributed capacity of the coils of the choke 13, and also in the condenser 14 if used, and is dissipated before reaching the other side of the tuned circuit. The charge which builds up will of course leak oil at a certain rate depending on the constants of the circuit, that is, if the radio frequency comes back strongly after fading then more current will pass absorbing energy from the tuned circuit. By putting the damping on the radio frequency side of the main circuit the time required to build up a charge on the condenser 14, (before it can be effective for damping purposes) is controlled by the choke value and by the capacity. This will take a longer time than the time interval of the lowest audio note, which in turn is the longest time interval of any. The actual averaging need only extend over half an audio wave of this lowest note, but it is preferable to average for several notes. As previously described, when once the receiving apparatus has been set to give a desired volume, the strength will be retained indefinitely, however bad the fading effects may be. The apparatus is of a simple nature and is believed to carry out the objects of the invention :inan vefficient and novel way.

Having described my invention, I claim:

1. In a radio receiver, a detector circuit including a tube provided with a tunable input circuit, a variable impedance path connected across said input circuit, said path comprising a rectifier in series with a source of direct current potential, and means associated with said potential source for adjusting the magnitude of potential thereof to a value substantially equal to the peak value of a predetermined minimum carrier voltage impressed upon said tunable input circuit, and a time constant network connected in series between said rectifier and said potential source.

2. In a radio receiver, a detector circuit including a tube provided with a tunable input circuit, a variable impedance path connected across said input circuit, said path comprising a rectifier in series with a source of direct current potential, means associated with said potential source for adjusting the magnitude of potential thereof to a value substantially equal to the peak value of a predetermined minimum carrier voltage impressed upon said tunable in put circuit, anda time constant network connected in series between said rectifier and said potential source, said network comprising a choke coil in shunt with a fixed condenser.

EDGAR D. TILLYER.

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