US2237895A - Impulse direction-finding receiver - Google Patents

Description

Aprii 8, 1941. e. ULBRICHT IMPULSE DIRECTION-FINDING RECEIVER Filed May 28, 1958 lnnentor Gunther ULbricht (Zttorneg Patented Apr. 8, 1941 res UNITED IMPULSE DIRECTION-FINDING RECEIVER Application May 28, 1938,-Serial No. 210,596 In Germany May 31, 1937 2 Claims.

In order to practice direction-finding with the use of waves, no matter how polarized, recourse is had quite often to impulse direction-finding. This'method is predicated upon the use of transmitter impulses which, in the direction finding receiver, after having been amplified are oscillographed, in most cases so that first an upright pattern results. But if, then, in addition to the sending impulses of the direct or ground wave, reflected impulses due to the space or sky wave (echoes) put in an appearance, the main impulses and the echoes may be distinguished from one another in that, owing to the dilference in the length of path of the direct and the reflected rays, the impulse patterns of the chief impulse and of the echoes are separately visible. If the indicator device consists, for instance, of a Braun tube, then the two impulses, that is, the groundwave impulse and the space-wave impulse, will be observed adjacent each other. In the methods known in the art the direction-finding loop is turned until the pattern set up by ground-wave impulses disappears.

Now, suggestions have been made in the prior art adapted to take bearings by ear rather than by eye by the use of optical direction-finding means as here mentioned. With this end in view, automatic volume control has been suggested which, upon the arrival of the main impulse causes the direction-finding receiver to be blocked for a short instant so that the impulse echoes are rendered ineffective. Hence, the time constant of the automatic volume control or gain regulation must be so brief for the blocking action that the gain will be decreased to a sufficient degree during the time intervening between the main impulse and the first impulse echo. 0n the other hand, the time-constant of the unblocking action must be so chosen that, on arrival of the main impulse full sensitiveness has been restored.

In such an automatically regulated impulse direction-finder, however, it is not yet possible to eifect minimum signal strength direction-finding by acoustic means; on the contrary, it is still imperative to use a Braun tube screen for the recording or reading of the signal. The underlying reason is that the impulse frequency is too low (say, around 50 cycles per second) so that there results no readily audible note. other hand, however, it is not feasible to shift the impulse frequency upward inside the tonefrequencyv range for this would result in disturbances in all receiver sets in the neighborhood as a result of the operation of these impulse On the transmitters. Practical experiments have demonstrated that it is entirely impossible to choose the impulse frequency, say, at 300 cycles per second, since the broad frequency band of these impulses would fall directly into the audible.

suppress pensated by incoming ground-wave impulses.

The basic idea of the invention shall be explained by reference to the appended drawing in more detail. Fig. 1 is a. schematic diagram used in describing the invention; Fig. 2 is a schematic circuit diagram of the invention; and Figs. 3 and 4 are graphs descriptive of the operation of the device.

In Fig. 1 is shown an amplifier tube R the grid of which is fed with the tone-frequency voltage U0 which, for instance, may be of 1000 cycles per second. Normally, the grid is subject to a marked constant negative biasing potential Eg so that in the plate circuit of the tube upon which the positive potential Ea is impressed, no sound will be audible in the telephone T connected to the output transformer U. Indeed, it is only when the biasing voltage Eg is cut down to zero, say, by being neutralized by a potential of opposite polarity, that the sound-frequency alternating potential will be amplified and rendered audible in the telephone.

Now, according to the present invention, compensation or neutralization of the biasing voltage Eg is to be eifected by causing the opening of the blocked tube by the incoming impulse signals (or signal impulses). An arrangement of this kind is illustrated in Fig. 2, where R1 the radio frequency rectifier tube is connected to act as a plate detector. If, then, radio frequency impulses reach the grid of this tube R1, audio frequency impulse signals will-be caused to arise across the outer resistance Ra which is shunted and bridged for radio frequency by the condenser C1, the said audio frequency impulses having a polarity as indicated in Fig. 2. These signals cause the unblocking of the audio frequency tube the impulse frequency of, say, 50 cycles per sec ond. The note of 1000 cycles per second sounds somewhat raucous, but it is audible, so that by turning the direction-finder frame the point of minimum signal strength is readily determinable.

It will be found convenient to reduce the coarseness of the note by tuning the output transformer U2 to the auxiliary frequency of 1000 cycles per second.

If by the aid of a rectifier G which in series with condenser C1 is paralleled to the outer resistance Ra, provision is'rnade that the condenser CI is rapidly charged, but discharged only at a slow rate of speed, still further improvement of the note is possible. The charge time by suitable choice of the value of the resistance r may be made so that CI, in the interval between two impulses, will just be discharged. Where conditions are as stated, the audio frequency which arises at the headset T2 has a form as plotted in Fig. 4. If the duration of an 'impuls'e'signal is less than a period of the auxiliary voltage U0, the increase of the charge time of C1 must be adopted as shown in Fig. 4.

I claim as my invention:

1. A detector for impulse waves including a source of audio frequency current, a thermionic tube including a cathode, a cathode lead including a resistor and a connection to said source of audio frequency current, a rectifier shunted by a second resistor connected in series with a condenser, said rectifier and series condenser being connected across said first mentioned resistor, and an audio amplifier effectively connected across said first mentioned resistor and said audio frequency connection.

2. In a detector of the character of claim 1, means for biasing said audio amplifier to cut off.

' Gt'iNTHER ULBRICHT.

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