US2073409A

US2073409A - Signaling system

Info

Publication number: US2073409A
Application number: US735767A
Authority: US
Inventors: John P Shanklin
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1934-07-18
Filing date: 1934-07-18
Publication date: 1937-03-09
Anticipated expiration: 1954-03-09

Description

March 9; 1937. J, p, SHANKUN 7 2,073,409

SIGNALING SYSTEM Filed July 18, 1934 QZL 0.5C/LL A 70/? I INVENTOR JOHN P. SHA KLIN ATTORNEY Patented Mar. 9, 1937 PATENT OFFICE SIGNALING SYSTEM John P. Shanklin, Riverhead, N.

Radio Corporation of America,

of Delaware Y., assignor to a corporation Application July 18, 1934, Serial No. 735,767

2 Claims.

This invention relates to a method and means for producing signaling currents, the character of which is representative of signals to be transmitted and a method of and means for converting interrupted signaling currents into signal indications or markings.

My method of and means for converting signaling currents into signal indications or markings also includes provision for eliminating to a large extent the effect on the indications or markings of weak signals caused by fading of the received wave.

The novel features of my invention have been pointed out with particularity in the claims appended hereto as required by law. The nature of ing, in

my invention and the manner in which the same is carried out will be understood by the following detailed description thereof and therefrom when read in connection with the attached drawwhich;

Figure 1 serves to illustrate the principle of my invention; while,

Figure 2 illustrates a practical application of my novel method and means relating to a receiving circuit. The diagram of this circuit shows only the essential elements, but there may also be included any other elements known in the art which will enhance the operation thereof.

In Figure 1 a radio frequency oscillator 01 is coupled to the input of a second radio frequency oscillator 02. The output of the oscillator 02 is coupled in turn to the input of a third radio fre quency oscillator 03. The oscillators are of the thermionic type and may include variable frequency determining means, and frequency controlling means.

With the oscillator 01 inoperative, 02 will oscillate at a frequency f1. If 01 is now put into operation, due to effects which will be explained 0 later 02 will operate at a new frequency f2.

Consequently the beat frequency produced between the high frequency oscillations of Oz and 03 will vary as the oscillator 01 is turned off and on. The oscillator 01 may be turned off in any manner such as by means of a key in one of the circuits thereof. By keying the oscillator 01 the beat frequency produced by 02 and 03 can be made to vary at signal frequency.

The principles of my invention are applicable 50 to means for converting signaling currents into signal indications or markings as well as to circuits for producing signaling currents. Such a converting circuit has been shown in Figure 2 in which A represents a signal absorbing system,

55 D1 represents a demodulator of the regenerative type having input and output electrodes connected in coupled circuits as shown, the input circuit being also coupled to the absorption system A. The regenerative demodulator D1 has its output variably coupled as shown by a condenser C to the input circuit of a second regenerative demodulator D2. This demodulator also has its input and output electrodes connected as shown in coupled input and output circuits. Each demodulator has an indicator connected as shown in its output circuit. The indicators shown may, of course, be replaced by additional amplifiers and/or recording apparatus. The demodulators D1 and D2 may be normally tuned to the desired frequencies by the variable capacities in the input circuits thereof. In explaining the operation of this receiver it may be kept in mind that the absorption system A may for some purposes be looked upon as the oscillator 01, the demodulator D1 may for some purposes be looked upon as the oscillator 02, while the demodulator D2 may for some purposes be looked upon as the oscillator 03.

By adjusting the coupling between A and D1 and the amount of regeneration the detector D1 may be caused to produce oscillations at a frequency determined by the elements in the circuit thereof when no signalis impressed onA, and to fall or be drawn into synchronism with the signal frequency when impressed on A.

In describing the operation of the receiver of Figure 2 it will be assumed first that the incoming signal is strong enough to pull the demodulator D1 into synchronism with the signal frequency. Suppose that with the signal absent D1 is tuned to oscillate at 1,000 cycles lower than the signal frequency, and D2 is tuned to oscillate 1,000 cycles lower than the frequency to which D1 is normally tuned. A 1,000 cycle beat note will then be heard in the telephones H. On introduction of the signal in A, D1 will shift to the signal frequency or be entrained thereby and a 2,000 cycle tone will then be heard in the indicators I-I. These two beat tones (telegraph mark and space) may be separated by a number of methods such as filters and the operators car. In practice it might be preferable to use the spacing tone frequency for indicating purposes since this tone is heard when no signal is re ceived in A and it is consequently constant in amplitude and in frequency. The second condition under which the system must operate is where the signal received at A is of reduced strength and insuflicient to entrain or pull the regenerative demodulator D1 into synchronism therewith. Although the signal does not entrain the oscillations of D1 and synchronize the same, it will neverthelem cause D1 to shift in frequency. In this case marking and spacing tones will be produced as-in the prior case and may be separated as before by the indicators H or by a filter circuit coupled to the output of either of the demodulators.

The principle upon which the device operates may be explained as follows. The change of frequency of the detector D1 when a signal wave is impressed thereon is due to two known effects. The first is the change of bias on the control grid of detector D1 due to the rectified signal current in the grid circuit thereof added to the rectified grid current already present when the tube is oscillating. This causes the detector to shift frequency, but not necessarily to synchronize with the signal frequency. The second effect results from the fact that the signal excites the detector at the signal frequency and hence tends to synchronize the detector D1 with itself. If the radio frequency voltages due to the signal in the demodulator circuit are greater than the radio frequency voltages generated by the tube itself, the tube and circuit will of course synchronize with the signal.

My method and means of signaling and of converting signals into marking and spacing is based on the fact that, under certain conditions, if an alternating voltage of one frequency fl is introduced in a circuit already oscillating at another frequnecy f2 there will be a change of the frequency of oscillation of the latter circuit which will now oscillate at a third frequency f3. f3 may or may not equal f1.

By using the principle of my invention, as explained above in connection with Figure 2, it becomes possible to receive a short wave telegraph signal through a narrow band pass filter, say 2,000 cycles broad. This is practically impossible using present day methods. .The use of a band pass filter gives a very noticeable reduction of static and is used extensively in long wavetelegraphy. The signal heard when using the method of reception described herein is of constant amplitude and the frequency stability of the tone heard depends only on the stability of the two local oscillators D1 and D2. The signal heard is not affected, within certain limits, by fading and by frequency shift of the incoming signal.

The band pass filter may be connected as shown in place of the head phones H in the output of the detector D2.

Having thus described my invention and the operation thereof, what I claim is:

1. In a device of the class described a source of modulated oscillations, a receiving circuit including two cascaded stages of oscillating demodulators, means for so applying energy from said oscillation source to the first of said demodulators as to cause its frequency to lock in step with the modulated oscillations, and means for so combining the output energies from the two said demodulators as to produce beat notes of different frequencies depending upon the characterization of the modulations from the first said source.

2. In a signaling system having three sources of oscillations, the method of signaling which includes the steps of deriving oscillations from each of the first two sources, causing the oscillations from the second of said sources to be locked in step with oscillations from the first of said sources, causing modulations to be applied to the oscillations from the first of said sources at a signaling rate thereby to vary the fundamental frequency of said oscillations, and causing oscillations from the second of said sources when varied in frequency to be variably heterodyned with oscillations from said third source thereby to produce beat notes the frequency of which changes at the signal rate.

JOHN P. SHANKLIN.