US1882862A - System for keying transmitters - Google Patents

Description

Oct. 18, 1932. I w, MOSER 1,882,862

SYSTEM FOR KEYING TRANSMITTERS Filed Jan. 13, 1926 *I I I I I P INVENTOR WILHELM M05ER A ORNEY Patented Oct. 18, 1932 WILHELM MOSER, OF BERLIN, GERMANY, ASSIGNORTO TELEFUNKEN GESE LLSCHAFT FUR DRAHTLOSE TELEGRAPHIE GERMANY I o1" BERLIN, GE MA Y, A CORPORATION F SYSTEM FOR KEYING TRANSMITTERS Application filed January 13, 1926, Serial No. 80,926. and in Germany March 7,1925.

The keying of tube transmitters for short waves is attended with a number of difficulties which manifest themselves upon the reception of such waves. In beat reception, for example, a far higher wave constancy 1s necessary than when working with longer waves. F or instance, if a 30-meter wave unclergoes a variation of only 9 th of one percent this means that the frequency (10 per second) will change by 10,000 oscillations per second. The beat tone is subject to fluctuation by an equal amount, with the result that proper sound-reading reception is rendered extremely difiicult.

It has been found that changes in the wavelength inside the said order of magnitude are associated with every change in energy of the transmitter tube. Consequently a keying method that would suggest itself can be exressed: ke in si nal=full ener k-e in p y D b O intermission=no energy, which method is readily applicable in connection with long waves, but is useful for short-wave work only when the operating means supply full energy also during the intermissions, in which instance the same must be destroyed by an add tional element or means. This results in a considerable enlargement and an increase in cost of apparatus.

The same end may be attained in a simple manner by detuned keying, in the presence of perfectly constant, or substantially perfectly constant energy. In the case of short waves, this method is especially suited for the reason that the wave variation has to be only very small in order to furnish a change in frequency suilicient for the reception of the keyed signals. 0

In telegraphic work on short waves it has been discovered that undamped telegraphic signals, to be sure, can be transmitted to very great distances, but that it is difiicult to locate the transmitting station in heterodyne reception, or to re-locate it after it has been lost on account of fading or atmospherics. It is well known that this difiiculty is not quite so great in the case of damped or modulated signal work.

However, in the case of modulated transmission, the question comes up again as to ing signals are modulated what the most suitable keyingmethod would be. The most correct method of keying is that from zero to full energy. However, since also in this'cas-e high wave-constancy is requirechprovisions must be made for an equalization of load to which reference was made above. If this complication is avoided, it is possible to work similarly as in the case of continuous wave work with detuned key- 'ing,'except that here the changes in the waves must be incomparably larger than with continuous wave transmission. The transmltter requires a by far'larger placeln the fre 'quency scale. 7 I

Now, the present invention discloses a new keying method adapted to solve the problem.

According to the invention, the modulation of keying signals and keying intermissions is chosen difierently in such a way that the keying-signals possess a definite-mode ofm'odelation from one key signal to'another, while the keying intermissions have another mode of modulation which is the same for each keying intermission.

The method may be practiced with either termissions as different as possible fromthat of the keying'signals for instance, the intermissions need not be modulated at all, that is to say, are sent und'amped, while the keying signals are modulated to the fullest extent or the inverse plan could be followed. I

' *Another method resides in that the modulation frequencies are chosen to be of difierent values, for instance, the key signals could be'modulated at a'frequency of 2000, while 7 .tlieint'ermissionscouldbe modulated at a he 9 quency of '200, or the int e zrmissions' could be modulated at some inaudible frequency. The method hereinbefore indicated could be combined'rea'dily with the detuning of the wave-lengths. In this manner thebest possible separation and differentiation between key dash, and space or keying intermission could be obtained.

In the following, a number of embodiments and arrangements adapted to the practicing of the method shall be described by way of example.

Fig. 1 shows an arrangement in which the degree of modulation is utilized.

Fig. 2 shows a diagram of connections whereby the signal or the intermission may be modulated.

Fig. 3 shows an arrangement whereby the frequency is modulated.

Fig. 1 shows an arrangement in which the degree of modulation of keying signals and keying intermissions is chosen so as to be of different value. The transmitting apparatus consists of a separately controlled tube transmitter comprising the oscillator tube S and the modulator tube H which operates upon the aerial A. The grid of the tube H is shut off from the couplingcircuit by the aid of the blocking condenser E. The grid direct current flows through the choke coil D1, connecting points or terminal G, and resistance R1 to terminal K, and from there by way of choker D2 to the heated filament. Modulation is efiected by way of the transformer T1" which is connected in parallel with relation to the resistance R1, and which consequently imparts to the grid of the main transmitter an additional alternating current component of the desired frequency. For the purpose of variation of the degree of modulation, a resistance R2 is inserted between Tr and R1 which may be short circui ted by the telegraph key T. It will be understood that when R2 is short-circuited the degree of modulation is naturally higher than when the key is open. Fig. 2 shows the direct current path and GK of the grid in the case where the keying signals are non-modulated and the keying intermissions modulated, or vice versa. The key is here dis osed in parallel with reference to resistance 1, and therefore parallel to the modulating transformer Tr. By closing the key, modulation ceases. According to whether the key is arranged to operate as a working oras a back contact, either the signals or the spaces will be modulated. Fig. 3 shows an arrangement which makes it possible to choose the modulation frequency of keying signals and intermissions of different frequencies either of radio or audio frequencies. The grid direct current flows here from point G through the series-connected resistances R1 and B2. In parallel relation to R1 is a transformer Trl, and in parallel to R2 a transformer T122, transformer Trl serving to transfer frequency N1 and T72 to transfer frequency N2. By means of key T provided with a working and a back contact, alternately the one or dered inoperative. Hence, according to the mode of connection it is possible to use either the one or the other frequency for the signals or for the spaces.

Having fully described my invention, what I claim is 1. in a transmitting system, a source of high frequency oscillations having its output electrodes connected with a load circuit,

a thermionic modulator tube, means for impressing oscillations from said high frequen- WILHELM MOSER.

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