US2110761A - Automatic volume control for radio receiving apparatus - Google Patents

Description

March 8, 1938. H. DIAMOND ET AL AUTOMATIC VOLUME CONTROL FOR RADIO RECEIVING APPARATUS 2 Sheets-sheet 1 Filed Dec. 27, 1955 March 8, 1938. H. DIAMOND Er AL AUTOMATIC VOLUME CONTROL FOR RADIO RECEIVING APPARATUS Filed Dec. 27, 1935 2 Sheets-Sheet 2 Patented Mar. 8, 1938 limiti AUTOMATIC VOLUTVIE CONTROL FR RADIO RECEIVING APPARATUS Harry Diamond and Francis W. Dunmore, Washington, D. C., assignors to the Government of the United States, represented by the Secretary of Commerce Application December 27, 1935, Serial No. 56,348

3 Claims. (CI. Z50- 11) (Granted under the act of March 3, 1883, as

amended April 30, 1928; 370 (B. Gr. 757) The invention described herein, if patented, may be manufactured and used by or for the Government for governmental purposes without the payment to them of any royalty thereon.

'Ihis invention relates to improvements in automatic volume control for radio receiving apparatus. The primary object is to provide an automatic volume control for a radio receiver in which the volume level is influenced only by the desired signal and not by an interfering signal 01 static. The invention is applicable where fixed modulation frequencies are used at the transmitter, such for example as 65 cycles and 862/3 cycles used at radio range beacons. In one form of our invention reeds tuned to these frequencies operate in the output of the radio receiving set, the output of the reeds (which is purely 65 and 86% cycles with all interferencel and static eliminated) is amplified and rectified and applied as a negative bias to the radio frequency tube of the receiving set, thus giving automatic volume control.

Prior to our invention it was customary to allov'v either some of the rectified carrier or the audio-frequency output to return to the grids of the radio frequency tubes as a negative bias, in order to give the automatic volume control feature. Thus any carrier or audio frequency which passed through the receiving set reduced its sensitivity and consequently the desired signal output. With this invention the set sensitivity is controlled only by the particular audio note or notes which it is desired to receive-for instance, assume a pilot desires to receive a radio beacon signal consisting of a carrier modulated at 65 cycles and 862/3 cycles, and Wishes to have the output signal level to the vibrating reeds held automatically at a substantially constant level as the input signal to the receiver is increased, due to the approach of the airplane to the beacon station. With our invention the output of the vibrating reeds serves to give the negative grid bias, and, since the reeds are selective only to the frequencies it is desired to receive, only these frequencies have an eiect in controlling thesensitivity of the receiver. In this way an interfering note or crash of static does not affect the sensitivity of the receiver (unless it overloads it), and therefore, the reed amplitude is not altered. With the old system interference would act to lower the sensitivity of the receiving set and consequently decrease the desired signal output.

In another form of our invention which will be illustrated and described, reed vibration is used to hold a substantially constant signal output from the receiver by the method utilizing the amplitude of reed vibration to tune or detune one or more of the r. f. stages in the receiver. Other uses for and advantages gained by the use of this invention will be more clearly understood by reference to the following description and diagrammatic drawings.

In the drawings- Figure 1 shows an application of the invention to a radio receiver for a radio beacon with carrier modulated at two radio frequencies,

Figure 2 shows another form of the invention.

In Figure 1 the output of the reed converter, which output operates the volume indicator, is ampliiied and rectified and applied to the grids of the radio frequency tubes in the receiving set to 'give automatic volume control. In this iigure the numeral l designates the receiver of the signals of the radio beacon. This includes radio frequency amplifying tubes 2 and 3; detector tube #i and audio amplifier 5. The output terminals of the receiver are indicated by the nu-` meral S which may be connected to a lovv pass filter 5a, the purpose of which is to provide an additional safeguard against frequencies higher than the beacon modulation frequencies of 65 cycles and 86% cycles from passing through the reed converters, presently to be described.

The numeral 'l is the terminal of the receiving set through which grids of tubes 2 and 3 receive their bias; 3 a double throw single pole switch with moving contact connected to terminal l.; 9 is one iixed contact grounded, and it) another fixed contact, the latter being connected to the minus end of a suitable biasing resistor in the circuit, the purposes of the parts just mentioned being the subject of presently following description.

The numeral ii designates a reed converter which consists of the 65 cycle reed i2 with which is associated the driving coil i4 and an 862/3 cycle reed i3 with which is associated the driving coil i5. These driving coils are connected to the output filter 8a. or directly to the output terminals 6. An output coil Iii is arranged to be excited by the reed i2, and H is a similar coil excited by the reed i3. The A, C. output of coil l5 is rectified by oxide rectifier i8, and the similar output of coil Vi is rectified by rectifier I9. The pulsating D. C. output from rectiiers i3 and i3 is connected in aiding polarities to the terminals of a resistance 2t. The common connection ltd from the rectifiers to the center tap conection wb of the resistor is through the course indicator coil 22 which operates a needle of combined instrument 32. This needle point gives a lateral guidance to the pilot and is operated by the difference in the voltages delivered by the rectiflers I8 and I9. The voltage drop across the resistor 2l! is produced by the sum of the voltages delivered by the rectiiers. Numeral 24 designates the signal volume indicator coil of the instrument 32, to which this voltage drop is applied. The coil 24 operates the pointer 25 which is arranged to indicate the strength of the beacon signal delivered by the receiver. The primary of an audio frequency transformer 28 is in series with the volume indicator coil 24 in the instrument.

A high capacitance electrolytic condenser 23 acts as a damping for the pointer 25, and as a shunt for the variable portion of the pulsating D. C. Voltage delivered by the resistor 2G, and the condenser 2| acts as damping for the pointer 25.

Transformer 28 has an output voltage on its secondary because its primary current is of a pulsating nature and the output from the secondary of the transformer is therefore proportional to the output from the 65 cycle and 86% cycle reeds in the converter II and to nothing else, and it is from this output that the control voltage is derived for holding the output signal level constant as will appear. A signal level adjustment resistor is shown at 2l which is set at a volume to give the desired signal level at which the automatic volume control is to hold the output of the beacon receiver. A condenser 29 in shunt with the secondary of the transformer 2B may be used when a low pass filter is not used in the receiving set output. The purpose of the condenser 29 is to shunt any frequencies higher than the 65 cycle and 86273 cycle which may have passed through the reed converter, due to magnetic coupling between coils I4 and I5, and I5 and I'I.

A type 75 electron tube is shown at 33 which may be of the duo diode triode type with the two diodes connected together, as indicated at forming the rectifying elements for the output oi' the triode portion of the tube 33. The control grid 34 of tube 33 is connected to the output of the secondary of the transformer 28. The numeral 3'! designates the cathode, and 36 is the plate of the tube 33. A resistor 3! is provided to give the grid 34 the proper negative bias and across the resistor 3i is a by-pass condenser 30.

The output from the plate 38 passes through primary of transformer 4I. 11D is a high frequency by-pass condenser serving a function similar to condenser 25, and 38 is a usual radio frequency by-pass condenser to cathode. Conductor 39a goes to the D. C. plate supply source and conductor 391) goes to the positive side of the lament supply source, and 39 designates a filament resister. The output of secondary of transformer 4I is rectified by the diode elements of tube 33 giving D. C. voltage drop across the resistance 42. The positive end of the resistor 42 is grounded and the negative end is connected through resistor 13 and switch 8 to terminal 'i of receiving d set I, which in turn is connected to the grids of r. f. tubes 2 and 3. The connection of resistor 52 to terminal 'i is made through double throw single pole switch B when the movable contact of switch 8 is on terminal i5. With switch 8, therefore, on contact i5, the grids of radio amplifying tubes and 3 receive a negative bias from the resistor i2 which varies in amount depending upon the strength of the signal delivered to set I. The stronger the signal delivered to set i, the greater will be the negative bias delivered to tubes 2 and 3, and consequently their sensitivity will be reduced to such that the signal output of set I will be held substantially constant. With switch B on contact 9, the grids of tubes 2 and 3 are grounded and the automatic volume control feature is inoperative; the set being then adaptable for manual volume control. Referring now to Figure 2, there is here shown another form of our invention in which the reeds operate in a different way to give the automatic volume control feature; that is to say, that instead of producing a negative bias the reeds tune and detune one or more of the radio frequency stages of the receiving set to give automatic volume control. In this figure, 45 represents the usual radio beacon receiver with input terminals 58 connected to the airplanes antenna 154. :i5 is the primary of the input coupling coil. il is the secondary of said coil which latter is tuned to the desired beacon signal by means of the variable condenser 58, and in shunt with this condenser are two parallel condensers whose capacitance varies with the amplitude of vibration of the 65-cycle reed 56 and the 862/-,-cycle reed 56. Plates 52 and 53 with reed 50 form one condenser in shunt with 58, and plates 54 and 55 with reed 56|, form the other condenser in shunt with 58.

Reed 55 is driven by driving coil 5I and reed 56 is driven by driving coil 51. These coils are connected to the output terminals 69 of the receiver. 59 is a radio frequency amplifying tube with its grid connected to condenser 58 and its plate to primary of coil 55. Secondary of coil 6I is shunted by tuning condenser 62 connected to the grid of detector tube 63. 54-55 is the usual audio frequency coupling transformer between detector tube 53 and audio frequency amplifying tube E5. The output of tube 66 passes through output transformer tri- 68 to output terminals 5S, which in turn may be connected to the driving coils 'I2 and "i3 of the tuned reed course indicator 15 having a (i5-cycle reed TI and an 86%-cycle reed it. This arrangement functions as follows: The beacon signal is tuned in with condensers 62 and 58. 58 is then tuned (by adding capacitance) until the desired amplitude of vibration (about 8 mm.) is obtained on reeds 'il and "I4, as well as on reeds 55 and 55. Now, if the signal level delivered to secondary 4l increases, this increase will go through the set and come back to driving coils 5i and 5'! and the reeds actuated by these coils will increase in amplitude, thus increasing the capacitance from condenser plates 52-53 to reed and from condenser plates 54 and 55 to reed 55. This increased capacitance being in shunt with condenser 58 will tend to further detune this condenser and thus reduce the signal to normal again.

We claim:

l. A radio receiver comprising a radio frequency amplifying means, a detector and audiofrequency amplifying means, two mechanicallytuned selective means coupling said audio amplifying means, a rectiiying means coupling each mechanically-tuned selective means, indication means for indicating the diierence in the pulsating direct current output of said two rectifying means and additional indicating means for indicating the sum of the pulsating direct current outputs of said two rectifying means, means for changing the sum of the pulsating direct current outputs of said rectifying means into alternating currents, means for amplifying said alternating currents, a third rectifyng means for rectifying and ltering said alternating currents and applying the resultant direct current to said radio frequency amplifying means in such man,- ner that the sensitivity of said radio frequency amplifying means is controlled by the amplified sum of the outputs of the said rst two rectifying means.

2. A radio receiver with electron tubes having grid filament and plate electrodes, said receiver having a plurality of output circuits each consisting of a tuned reed with coil actuating means each of said reeds being mechanically tuned to substantially a different frequency, coil generating means associated with each of said reeds for deriving alternating current of constant frequency from the vibration of said reeds, means for rectifying said derived alternating current and means for impressing said rectified alternating current onto the grid electrodes of certain of said electron tubes for controlling the sensitivity of said radio receiver.

3. A radio beacon course indicator comprising a radio receiver with input and output circuits, two tuned reed lters each tuned to a different frequency With input and outputcircuits,

said input circuits being connected to the output of said receiver, rectifying means, with input and series connected output circuits, the input of each rectifying means being connected to a different one of the output circuits of said tuned reed filters, a resistor, the pulsating direct current output of each rectifying means being connected in opposition to the terminals of said resistor, a dual indicator instrument with two coils and associated pointers, a transformer, one of the coils of said instrument being connected across said resistor through the primary of said transformer, the other coil being connected to the center of said resistor and the series connection between the two rectiers, amplifying means connected to the` secondary of said transformer, and rectifying and filtering means connected to the output of said amplifying means, the output of said filtering means being connected to said radio receiver in such manner that the output of said filtering means controls the sensitivity of said radio receiver.

HARRY DIAMOND. FRANCIS W. DUNMORE.

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