US2049677A - Heterodyne receiver - Google Patents

Description

Aug. 4, 1936 R, URTEL 2,049,677

HETERODYNE RECEIVER Filed Dec. 30, 1932 INVENTOR RUDOLF URTEL W ATTORNEY Patented Aug. 4, 1936 omreo stares HETERODYNE RECEIVER l tii dolf Urtel, Berlin, Germany, assignor to Telefunken Gesellschaft fur Drahtlose Telegraphic m. b; H., Berlin, Germany, a corporation of Germany Application December 30, 1932, Serial No. 649,484

' In Germany December 9, 1931 a 4 Claims; (Cl. 250-20) My present invention relates to superheterodyne receiving systems of the type wherein a single tube is used as a combined local oscillatorfirst detector.

In the drawing Fig. 1 shows a combined local oscillator-first detector circuit of a type known in the prior art,

Fig. 3 shows a combined local oscillator-first detector circuit embodying the invention,

Fig. 2 shows the negative resistance characteristic of the screen grid circuit of the tube in Fig. 3.

In heterodyne receivers the functions of the first rectifier and the heterodyn-e are often fulfilled by one tube. An arrangement of this kind is shown in Fig. 1 comprising the use of a twin-grid tube I, one grid of which is associated with the input circuit (EF) (for incoming waves), while the sec ond grid circuit contains the circuit (UF) tuned to the heterodyne or local oscillation frequency. This circuit is excited by regeneration (RK) from the plate. From the plate circuit is derived the ensuing intermediate frequency (ZF).

Since in the use of screen grid tubes the working conditions that are most favorable from the viewpoint of amplification coincide with the conditions that are conducive to screen grid secondary emission of electrons, and, thus, provided suitable materials are used, to drooping characteristics IG=f (VG) (Fig. 2) the negative resistance represented by the screen grid circuit is utilized for wave generation by that, for instance, the circuit (UF) tuned to the heterodyne wave is in serted in the lead brought to the screen grid, (Fig. 3). Since in practice there result negative resistances of 150,000 ohms (smaller values being attainable by promoting the elfect), it will be seen that the condition for self-excitation ZZR is readily attainable, where Z is the impedance of circuit UF.

' The circuit scheme shown in Fig. 3 distinguishes itself by great simplicity (omission of supplementary feed-back circuit elements), and in addition it offers advantages as regards constancy and shape of the frequency curve.

The signals in Fig. 3 are impressed on input circuit EF, and the latter is coupled between the control grid and cathode of screen grid tube I. As stated above, the screen grid tube operating conditions are the same as when the tube operates as an amplifier; hence, the plate P is at a positive voltage, and the screen grid SG is at a positive voltage substantially less than that of to the desired local oscillation frequency, and the intermediate frequency is derived from the circuit ZF in the plate circuit. Suitable by-pass condensers C are employed to by-pass radio frequency currents from the screen grid and plate circuits.

While I have indicated and described one system for carrying my invention into efi'ect, it will be apparent to one skilled in the art that my invention is by no means limited to the particular organization shown and described, but that many modifications may be made without departing from the scope of my invention as set forth in the appended claims.

'What is claimed is:

1. A dynatron oscillator-detector comprising a tube having a cathode, control grid, anode and screen grid, both anode and screen grid being positive relative to the cathode, the screen grid being sufficiently less positive than the anode to impart a negative resistance characteristic to the screen grid circuit, a tunable signal circuit between the control grid and cathode, a tunable local oscillationcircuit in the screen grid circuit adapted to generate local oscillations of a desired connected between the controlgrid and cathode, 3

an intermediate frequency circuit connected to the anode of said tube, a tunable local oscillation circuit connected to the screen grid of said tube, said screen grid being free of any regenerative couplings to any other electrode circuit of said tube, the anode and screen grid being at a positive potential with respect to the cathode, and the screen grid potential being sufiiciently less positive than the anode potential to introduce a negative resistance into the screen grid circuit.

3. In a sup-erheterodyne receiver, a combined first detector and local oscillator network comprising a screen grid tube, a tunable signal circuit connected between the control grid and cathode, an intermediate frequency circuit connected to the anode of said tube, a tunable local oscillation circuit connected to the screen grid of said tube, said screen grid being free of any regenerative couplings to any other electrode circuit of said tube, the anode and screen grid being screen grid potential being sufilciently less than the anode potential to impart a negative resistance to the discharge space between the cathode and the screen grid, a signal input circuit connected between the signal grid and cathode, a local oscillation circuit in the screen grid circuit tuned to a frequency differing from the signal circuit frequency by a desired beat frequency, a resonant circuit connected to the anode of the tube and tuned to the beat frequency, said screen grid circuit being free of any regenerative cou-- pling with any other electrode circuit of the tube.

' RUDoLF URTEL.

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