US2000084A

US2000084A - Short wave receiver arrangement

Info

Publication number: US2000084A
Application number: US565025A
Authority: US
Inventors: Lewis Harold Miller
Original assignee: Hazeltine Corp
Current assignee: BAE Systems Aerospace Inc
Priority date: 1931-09-25
Filing date: 1931-09-25
Publication date: 1935-05-07
Anticipated expiration: 1952-05-07
Also published as: DE669919C

Description

May 7, 1935; H, M. 1. w|s

v SHORT WAVEYRECEIVER ARRANGEMENT Filed Sept. 25-, 1931 w M w R mu n MI M m 0 m n IM A D L mm AM w 52 mm 5320mm Sw x m 0 Q \QN Patented May .7, 1935 UNITED STATES 2,000,084 snon'r wave RECEIVEB'ARRANGEMENT Harold Miller Lewis, Douglaston, N, Y., assignor to Hazeltine Corporation Application September 25. 1931, Serial No. 565,025

' 2 Claims. (01. 250-20) The present invention relates to ashort wave tuning system known as a short wave converter, for use in conjunction with a radio broadcast receiver. Such a converter operates to receive short wave signals and convert them, on the superheterodyne principle, into currents of a frequency within the frequency range of the broadcast receiver. Thisfrequency will be referred to hereinafter as the intermediate frequency. The broadcast receiver serves as an intermediate frequency amplifier and audio signal output.

In operation, the broadcast receiver is tuned to some frequency within the broadcast band, and it may be that the frequency selected is the same as that being used by some transmitting station within the range of the receiver. However it is to be understood that it is not desired to receive such a signal at that time, but to receive some short wave signal, using, however, the frequency of the undesired signal as the intermediate fre- In operation, the usual converter receives and amplifies signals of the frequency to which the broadcast receiver is set to'respond and it also permits the reception of undesired signals which beat with the intermediate frequency produced by the converter and cause unpleasant interference. 1 Y

The broadcast receiving apparatus is itself usually shielded and would not receive the signal directly, but, however, the undesired signal, if it were of considerable strength, might be picked up on the lead or connection between the converter and the broadcast receiver, or might, in 35 fact, be picked up by the antenna and be amplifled by the modulator of the converter and passed through the connection to the broadcast receiver. It is the object of the present invention to overcome the above noted difliculty in connection 40 with the use of the converter method of short wave reception, and to provide means for preventing the receptionof signals of the intermediate frequency to which the broadcast receiver is tuned, whether such signals are directly picked 5 up or come through the converter itself. This and further objects of this invention will become apparent from the following specification taken in connection with the appended claims and the accompanying drawing.

50 In accomplishing the object of the present invention the leads between the converter and the broadcast receiver, as well as the wiring and circuit elements of the converter itself, are completely shielded. In addition, the antenna input 65 circuit of the converter is provided with a trap which would act as an amplifier thereof. 5

The plate supply of the modulator tube contains a tuned radio frequency choke which is tuned roughly to the intermediate frequency and thereby tends to by-pass currents of frequencies differing greatly from the intermediate frequency,

and which have been received by the converter. Having thus -briefly described the elements comprising the present invention, attention is invited to the accompanying drawing in which the single figure represents a circuit diagram of a converter embodying the present invention.

Referring now more particularly to the drawing, the antenna circuit includes the antenna ill, the ground I I, the trap circuit i2, comprising the inductance l3 and condenser M, the primary winding l5, and a portion of the secondary windingit. The inductance i3 and the condenser H of the trap circuit i2 are so proportioned that said circuit is resonant to the intermediate frequency produced by the short wave converter. The input circuit of the converter is connected to the grid of modulator device H, which may be any thermionic tube, though that shown is of the screen'grid type. The input circuit is tuned by means of the condenser 2|, which may be .a double condenser employing, as shown, a single rotor and two stators so arranged that the capacity obtained between the rotor and one stator is'maximum, when the capacity between the rotor and the other stator is minimum. The con- 36 nections to the stators are controlled by means of the switch 23. The actual condenser includes two stators and two rotors, so arranged that when onerotor is entirely within its stator, the other rotor is entirely out of its stator. This is 40 fully described in the application of William A. MacDonald, for Condensersfl Serial No. 564,997, filed concurrently herewith. Ihe function of the condenser and switch arrangement will be explained later.

The tapped secondary I6 is connected by means of switch 24, so that any of the tapped portions of the secondary may be included in the inputcircuit. The switch is so connected that the unused portions of the winding are short-circuited.

.For producing the heterodyne frequency for combining with the incoming signal and thus producing the intermediate frequency, there is provided the oscillator 25. This oscillatortube is of the single grid type and. includes in its grid 3 circuit the secondary of the oscillation transformer, the primary 42 of which is connected in the plate circuit which includes stopping condenser 43. The secondary 40 is a tapped winding similar to IE of the antenna transformer, and the connections to said secondary are controlled by means of switch 34. The grid return of the oscillation circuit is completed through the biasing resistor 21, which is connected to the cathode of the tube 25. The frequency of the oscillation circuitis determined by means of condenser 3|, which is similar to condenser 2|, and is connected to be operated therewith in a uni-control manner by means of the control knob 22 associated with the indicator dial 26.

The connections to the'two portions of the condenser 3| are controlled by means of switch 33.

Padding condensers 4| M and S are provided across the two portions of condenser, as shown, for the purpose of aligning the oscillation circuit with the input of modulator I1 in the middle wave range and short wave range, respectively. Padding condenser 4IL is connected across the long wave portion of the inductance winding 40, so that when the switch 34 is on contact L this condenser is practically in shunt with the condensers 3| and US for adjusting the alignment in the long wave range. When the switch 34 is on contact M, the condenser 4IL is in shunt with condensers 31 and 31', and the total series capacity is at that time the sum of these three condensers.

In series with condenser 3| are provided

series condensers

36, 31 and 38, the connections to which are controlled by means of the switch 35. Each of these condensers is provided with the padding condenser 36', 31', or 38, respectively, for the purpose of correcting the alignment of oscillator circuit with the modulator input in the various frequency bands. In the middle frequency band, as has just been stated, the condenser 4 IL is in shunt with 31 and 31. Coupling coils 44 and 45 coupled to the middle and long Wave portions of the secondary 40, respectively, are included in the cathode circuit of the modu lator I 1. This circuit also includes the biasing resistor 46 shunted by by-pass condenser 41 for the purpose of causing tube H to act as a modulator.

The plate and screen grid potential are provided by means of the power supply source 20 which, as shown, is of the ordinary double wave rectifier and filter type. This power supply also provides heater current for heating the cathodes of tubes l1 and 25. A resistor 29 is included in the plate lead of the modulator 25 for the purpose of reducing the plate potential thereof.

The circuit elements of the converter are shielded as indicated by the dot-dash line which encloses them in the drawing. Any appropriate shielding means may be used. For instance, the usual metal chassis, which is constructed to enclose and shield the various elements attached to it, may be used.

As shown, the dial 26 includes three scales, 26a, 26b, and 26-c, these scales covering the short wave band, middle wave band, and long wave band, respectively.

It is to be noted that in order to get better spacing of the frequency indicator, the short wave scale is placed in the outer position on the dial 26, as the condenser motion to get the frequency separation required to separate the various stations is less in the short wave hand than it is in the long wave band.

For the purpose of indicating in which of the' frequency ranges the converter is operating, each of the scales is provided with one of the illuminating lights 1la, 11-12, or 1lc, controlled by means of switch 39 to light them when tuning through the short wave band, middle wave band.

and long wave band, respectively.

Switches

23, 24, 33, 34, 35 and 39 are so arranged as to be simultaneously operated and also to be actuated by the control knob 22 as the condensers are tuned through the limiting capacities for one of the frequency bands. Thus, the rotation of the control knob22 results in the actuation of the switches 23 and 33, resulting in switching of the connections to condensers 2| and 3|, respectively, to give the opposite capacity extreme for the modulator and oscillator circuits. Switch' 39 is simultaneously operated changing the lighting of the indicating lights and thus indicating the change in the frequency band by changing the indication from one to another of the scales. The specific means for actuating the switches constitute no part of the present invention, but are described fully in application of Harold Miller Lewis for Switching arrangement, Serial No. 565,026, filed concurrently herewith.

Included in the plate supply to the modulator I1 is the inductance 50. This inductance may have a high inherent capacity as indicated by capacity 5 I, or an actual condenser may be placed in shunt therewith. The inductance and capacity, however, are so proportioned that frequencies differing greatly from the desired, intermediate frequency will be by-passed.

A connection from the output of modulator I1 is made through condenser 52 and lead 53 to the antenna binding post of the receiver 51. This connection is made through a shielded cable 54, which may, for example, be a BX cable, from the walls of which the lead 53 is spaced by means of bakelite spacers 56. This spacing is necessary to prevent loss of signal energy, and to prevent too high a capacity in the connection between the converter and the receiver 51.

Also connected through the cable 54 is the ground connection 55, which is connected to the ground binding post of receiver 51. The capacity 52 and the inherent capacity between the

leads

53 and 55 are so proportioned that they constitute a dummy antenna to properly load the modulator I1, and to prevent misalignment of the input of receiver 51. tween the antenna l0 and the lead 53 by means of which the antenna may be directly connected to the input of the receiver 51 when it is desired to receive signals in the broadcast band directly on receiver 51.

The receiver 51 may be of any well known type, and is provided with the usual sound reproducing device 58. The specific details of neither 51 nor 58 constitute any part of the present invention.

The receiver is tuned to the intermediate frequency which it is desired to utilize, preferably 1,000 kc. The direct reception of signals of 1,000 kc., when the set is being operated to receive short wave signals by means of the converter, is

prevented by means of the shielded cable 54. The

modulator is prevented from acting as an amplifier of signals of 1,000 kc. frequency by means of trap circuit l2. Any signals of a frequency other than 1,000 kc. in the output of modulator 11 would be by-passed through the inductance 50. It is thus seen'that a number of provisions have been made to prevent the interference of broad- Switch 59 is provided be-- cast signalswith the short wave signals'being received by means of the converter.

In the event that the converter constructed in accordance with the present invention is made to cooperate with any specific broadcast receiver,

.the inductance l3 and condenser ll of the wave trap I! may be matched to the tuning inductances and condensers, respectively, of the receiver so that the wave trap may be tuned by a similarsetting of its control element to any wave length to which the receiver is adjusted.

If it is desired, the converter and broadcast receiver may be combined in a single unit, and in this case the condenser M may be connected to be operated simultaneously with the tuning condensers of the broadcast receiver II, as indicated by the dotted line connecting it and the broadcast receiving condenser generally indicated at C. with this arrangement, therefore, signals of the wave length which the broadcast receiver is at any instant set to receive are, by the simultaneous tuning of the trap circuit, automatically prevented from reaching the modulator of the converter to beamplified thereby.

To recapitulate, the circuit It acts to prevent currents of the intermediate frequency being received over the antenna II and amplified by the modulator II, the shielding of the lead It prevents a direct pick-up between the output of the device I! and the input of the radio broadcast receiver, and the shielding of the converter prevents the pick-up within the converter itself.

It is obvious that a band-pass fiiter might be used in place of the simple wave trap shown. In

this case the complete broadcast band wculd be excluded from the converter so that the intermediate frequency could be changed as desired to prevent interference with a particularly strong broadcast signal. 1

Full details of the above described circuits, including the characteristics thereof, are given in the copending application of Harold Miller Lewis for Short wave converter, Serial No. 565,024, illed concurrently herewith.

Full details of the mechanical arrangements for actuating the various switch mechanisms are given in the application of Harold Miller liewis for Switching arrangement", referred to above.

I claim:

1. Short wave receiving apparatus which comprises a converter, for converting short wave signals into long wave signals, said converter including a trap circuit comprising a fixed inductance and a variable condenser in its input circuit for preventing impressing signals of a long wave length directly upon the input of said converter, a radio broadcast receiver connected to .said converter, and means connecting the tuning elementof said wave trap with the tuning element of said broadcast receiver, whereby saiclv trap circuit will be simultaneously tuned to the wave length to which said broadcast receiver is tuned to prevent impressing-signals of the long wave length by said converter upon said broadcast receiver.

2. In a radio receiver including a first portion adjustably resonant to signal frequency voltages, a second portion variably resonant to voltages substantially different in frequency from those of said first portion, selective impedance means connected in said first portion and tuned to the frequency of said second portion to reject from said receiver signal voltage of the frequency of the signal voltageof said second portion, and uni-control means for simultaneously tuning said second portion and said selective impedance means of said first portion.

' HAROLD MILLER LEWIS.