US2097880A - Radio receiving system - Google Patents

Description

Nov. 2, 1937.

P. HERMANSPANN 2,097,880

RADIO RECEIVING SYSTEM Filed Feb. 12, 1934 IN VEN TOR B4 01%? mam/w BY A T TORNE Y Patented Nov. 2, 1937 Paul Hermanspann,

Berlin, Germany, assignor to Telefunkeii Gesellschaft fiir Drahtlose Telegraphie m. b. H., Berlin, Germany, a corporation of Germany In Germany February 14, 1933 Application rii aiy 12, 1924, Serial No. 710,812

1 Claim.

The reception of broadcast receivers in large cities is markedly impeded and impaired and sometimes even rendered entirely impossible as a result of stray noises. The main sources of dis- 5 turbances in radio reception in a large city are due mostly to commutators of motors, high-frequency therapeutic apparatus, crackling noises caused by the operation of switches, etc.

Investigation has shown that these disturbances are mostly due to coupling between the room or indoor antenna and the lighting circuit and possibly also gas and water mains. The suggestion has therefore been made to erect high antennae and to connect these by means of capacitively shielded leads with the input of the receiver. As a matter of fact, such antennae installations mostly insure great freedom from disturbances. Their demerit primarily resides in the amount of labor, material and cost they involve.

Further research has shown that the above disturbances have practically no closed magnetic fields. The attempt has therefore been made to render receivers free from trouble by the use of coil or frame antennae, though it has been discovered that such an aerial operates under conditions free from trouble only under certain circumstances.

The situation ure 1.

Fig. 2 shows a device culties.

Referring to Fig. 1 of the drawing, R. denotes the coil antenna which is tuned by the variable condenser C to the wave to be received, and which is connected with the grid of the input receiver tube M, the cathode end of this circuit being united with ground potential. The lighting or distribution circuit L 'is a source of disturbing voltages occasioned by motors or the like. Between L and R there exists a capacitive eifect denoted by capacity C0. The disturbing oscillations flowing to ground byway of this capacity and the input circuit will then experience a considerable fall of potential at the tuned coil antenna.

Now, this invention shows and discloses a simple way to render a coil-antenna equipped radio receiver insensitive to such disturbances, and which at the same time, looked at from a purely constructional viewpoint offers important and advantageous features so far as the practice of receiver building is concerned.

According to the invention, an aperiodic loop 55 or coil antenna is employed which is inductively is depicted graphically in Figfor overcoming these difficoupled with the tuned input circuit of the receiver in such a way that the impedance of the coupling inductance is low compared with the impedance of the coupling capacity between the loop and the disturbing lines or circuits. Under normal conditions the capacity establishing coupling relations with the loop is approximately of an order of magnitude of 20 cm. In normal radio receivers it has been usual practice to employ mostly tuned loop circuits which, for the useful wave, had an impedance of about 100,000 ohms.

But in the scheme of this invention the input circuit is not tuned, and merely the impedance of the coupling inductancemust be so chosen that its reactance for the useful wave will be substantially lower than the reactance of a capacity of about 20 cm. Suited for this purpose are inductances of an order of magnitude of 25,000 cm. and less.

The invention is explained in more detailby reference to Fig. 2 of the drawing. The loop is in coupling relationship with the tuned circuit G by way of the low and unilaterally grounded inductance L1, said circuit G being connected with the grid of the amplifier tube M. Li has one pole united with earth potential, although, of course, also the middle of L1 or some other point of L1 may be connected so as to be at ground potential. The disturbing line L shall be supposed to carry stray oscillations and shall have a coupling capacity Co to the loop antenna. If, then, for the wave to be received, wLi is made low compared to it will be readily understood that the stray oscillations issuing from L and leaking to ground by way of C0 and R will be unable to set up any practically appreciable fall of stray potential across L1. Suppose that \=500 meters, Co as is normally true =20 cm. and L1=1500 cm., then the capacity coupling resistance is approximately 12,000 ohms, whereas wLl will be about 5 ohms only. The invention offers practical merits in various regards for receiver construction; for instance, the loop antenna may have the nature of a single-loop ring, while there exists this additional chance that the loop may be unilaterally grounded.

Since in order to obtain satisfactory volume in reception a close coupling between the loop circuit R and the input circuit L2 G is recommendable, it is furthermore convenient to use a transformer L1 L2 of the rf type with compressed iron powder core. In this arrangement the incoming volume will not be impaired because by the reception of the useful waves the magnetic field is The operation of the device may be understood from the following, taking for instance Fig. 1, it is evident that a sudden pulse of voltage impressed upon the loop travels directly through 'to the grid. .In Fig. 2, due to'the low impedance of L1, little voltage can exist across it and therefore the tuned circuit is excited almost solely by magnetic coupling. Obviously electrostatic disturbances do not set up currents in a loop circuit, for the reason that it is'a closed circuit and responds only to magnetic disturbances such as are caused by the desired signals. 7

I claim:

In signalling apparatus, a relay circuit provided with input terminals and output terminals, a tunable circuit connected across the input terminals, said tunable circuit comprising an inductance 'coil and a variable condenser, said latter being shunted across the coil, means connecting one end of the coil directly to ground, an untunecl loop circuit including a. loop and an inductance coil forming a closed circuit, inherent capacity between the loop circuit and a source of disturbing energy through which disturbances are transferred to the loop circuit, said second inductance coil having a low impedance value as compared to the impedance of said inherent capacity, means for closely coupling said two inductance coils including a core made up of powdered magnetic material.

PAUL HERMANSPANN.

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