US2072268A - Transmitter for electromagnetic waves - Google Patents

Description

' March 2, 1937. E. KRAMAR TRANSMITTER FOR ELECTROMAGNETIC WAVES Filed April 2, 1955 JR E R2 W M 2 fzzvenfar: fmsf/framar Patented .Mar. 2, 1937 arses TRANSIWITTER F033 ELECTROMAGNETIC WAVES Application April 2, 1935, Serial No. 14,212

In Germany April 6, 1934 1 Claim.

In the copending patent application Serial No. 638,907, filed October 21, 1932, issued January 21, 1936, as Patent No. 2,028,510 for Transmitters for electromagnetic waves, radio beacons are de- 5 scribed by which two radiations different in directionality are emitted alternately by a device that has an antenna continuously energized by a high-frequency generator, and reflectors which are keyed. The keying is such that a combina- 10 tion signal is obtained in the angle of overlap of the two radiations, namely a continuous dash which shall indicate to the pilot of an aircraft, vessel or the like whether he is on or ofi' the course to be followed. For instance, the Morse letter 15 A may be emitted in one direction and the Morse letter N in the other, or in one direction merely dots and in the other merely dashes are sent out, the latter method being adopted by preference. The aerials may in the 20 simplest case be simple dipoles.

Experiments have shown that this continuous dash signal is to perfection and constant only if care is taken that there be no decrease in energy when changing from one component signal to the 5 next. In order to perform this, complicated arrangements of relays have been proposed which are to cause each reflector to become effective at exactly the same moment the other reflector becomes ineffective. The keying devices re- 30 quired to such end are, however, extremely complicated and above all must be attended very care fully in order that the drawback which was to be obviated not recur due to a longer service. The continuous dash is impaired also if a reflector becomes ineffective too early. It will thus be readily seen that the object aimed at here is not easy to attain by this means.

The invention described hereafter proposes to so elect the radiation diagrams that the characteristic curves of radiation which are produced by keying the reflectors shall intersect on the characteristic curve of the energized antenna, i. e. the curve which there is if the reflectors are ineffective.

45 This willbe understood from the following description, reference being had to the accompanying drawing in which Fig. 1 is a diagrammatic elevation illustrating an example of an antenna system of the said kind.

50 Fig. 2 is a diagram relating to the operation of the system. Fig. 3 is a diagram similar to that of Fig. 2 but showing the invention.

A dipole E is continuously energized by the transmitter S. On both sides of the dipole E 55 and in line therewith are arranged two dipoles RI and R2, which act as reflectors. These reflectors are interrupted in the middle and may be closed by relays M! and M2. Instead of interrupting the reflectors, it is possible to provide for them to be detuned, for example. The re- 5 lays MI and M2 are alternately energized and de-energized by a commutator K, which is driven by a motor A. It is assumed in the drawing that the dipole R! is opened, that is inactive, and the dipole R2 closed, that is active. Instead of the collector, a relay device may be employed, which is so arranged that both relays are keyed in par-' allel and thereby the contacts of the one closed and those of the other opened.

Fig. 2 shows the radiation conditions. If both reflectors RI and R2 are opened, the horizontal characteristic of the energizer dipole E is a circle a. If only the reflector R2 is closed, the characteristic c is obtained.

This arrangement which preferably operates with ultra-short waves, is quite suflicient for the purpose in view, that is the directional characteristics are sufiiciently intense, as the point of intersection of two characteristics is utilized, for example, the point of intersection PI of b and c. Fundamentally, however, any other point of intersection, such for example as is shown by point P2, is suitable. It is therefore not always necessary to operate with two reflectors which are alternately keyed. A single reflector is quite sufficient for a simple device.

In accordance with the invention the point of intersection P of b and c is on the circle a, as shown in Fig. 2.- If this point were at Pl, as represented in Fig. 2, then the following would result.

If in the point Pl the curve 1) changes into curve 0 without there being a difference of time between the signals constituting the continuous dash then this dash is to perfection. This is the very result which as stated herebefore has been aimed at by means of complicated arrangements of relays. If, however, a reflector becomes active later than the other becomes inactive, then at the receiving place the loudness increases from PI to P during the said difference of time, because when both reflectors are ineffective the energizer dipole E is radiating alone, the field intensity thus corresponding to the radiation characteristic a, that is to say, a slight modulation is superposed on the continuous dash in accordance with such increase in energy. When both reflectors get active for an instant the energy increases from Pl to P2.

The described drawback can not occur if, as

suggested by the invention, the radiation characteristics are so arranged that the point P of b and 0 shall be on a. If the keying is effected in a retarding manner then during the intervals between the signals there will be an emission corresponding to the circle characteristic a, but the amplitude will not increase, as may readily be seen from Fig. 3. Thus, it is only necessary to provide for the keying to be retarded, i. e. care should be taken that the two reflectors are never out in at the same time. This is easy to perform by means of a simple collector, since the relays act by themselves to establish a certain small retardation.

What is claimed is:

A radio transmitting arrangement comprising, a main antenna, a high frequency generator the amplitude of the wave radiated from the main antenna when assisted by either of the reflecting antennae is equal to the amplitude of the radiation in said direction from the main antenna acting alone.

ERNST KRAMAR.

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