US1958954A - High frequency transmission - Google Patents

Description

W 1934 J. PLEBANSKI HIGH FREQUENCY TRANSMISSION Filed July 9, 1950 2 Sheets-Sheet 1 15, 193. J. PLEBANSKI 958,954

HIGH FREQUENCY TRANSMISSION Filed July 1930 2 Sheets-Sheet 2 STATES HIGH FREQUENCY TRANSMISSION Jozef Plebanski, Warsaw, Poland Application July 9, 1930, Serial No. 466,841 In Poland July 10, 1929 2 Claims. (Cl. 179-171) It is known that in telephony or telegraphy Figure 3 shows a valve frequency characterisover wires or without wires with high-frequency tic, currents the modulation efiects an alteration Fig. 4 is a circuit diagram showing a tuned in the amplitude of carrier wave, which is equivacircuit coupled to an artificial line. lent to originating three waves according to the The basic idea of the arrangement described figure, in the case of modulation with one audio is theutilizing of an intermediate independent frequency. drive system D1 acting through or without an am- MA t+B t t plifier on two circuits 1 and 2 detuned in relation Sm Sm Sm p to one another, so that the currents induced in valves a and d are phase-shifted relatively to one another. Instead of circuits at and d any arrangement producing relative phase-shifting can be used.

Now if we modulate the oscillations in the valve As the speech or other sounds are composed of a number of different audio frequencies, it follows that a modulated wave is composed of a non- 1o modulated Carrier of frequency a by audio frequencies from a line Z through a transformer T1 and a modulating valve M1, then 3, in the circuit 1 we shall have an ordinary modu- 21r lated wave. If the modulated wave is now passed a right side band of frequencies ranging from through a fi te which cuts u one modulated 20 side band and adds through a circuit 2 some 1+ 30 phase of the carrier wave from the drive D1, after demodulation by the valve d we shall obtain in to the transformer T2 the same audio frequencies w as in T1, but phase-shifted, because 25 gr -I- 10000 80.

B 2 A cycles per second, and a left side band of frequen- 1d a2 I: Sm (wt-H) 2 cos p) cies ranging from 1s arrangement for the phase-shifting of to audio frequencies is exactly described in my Patw ent No. 1,858,936. The phase shift can always 21r be so adjusted as to be equal to 4 0 is, 10000 cycles. By using one side band with the '50 by way of example in the accompanying drawcycles per Second It is obvious that for telephonic transmission As is known, only one Side band, for instance it is important to have the relative phase shift the left side band, is necessary for reception. In of all frequencies equal Therefore the Such a system the entire fre band radiated filter F must have such a characteristic that all will be not 20000 cycles but only half of that, that frequencies of the one Side band Passed will have the same or about the same phase. Otherwise,

after detection in the transformer T2, the audio frequencies will not all be phase shifted at 90 to original frequencies in T1. In my opinion the carrier it is possible, in a frequency range from 200 to 2000 metres, to utilize far more broadcasting stations than under existing circumstances utmzing both side bands. most suitable arrangement for this purpose W111 45 systems of one side band modulation with be the filters described in my British specification m1) rier elimination are known and utilized in prac- 211,151- tical work. They have however various disady now m0d1l1at1ng,thr01lgh modulatlng valves vantages which are obviated in this invention. g a d M2, the valves 01 and O2 fed from the The invention is diagrammatically illustrated v but Wlth relatlve p e Shift of 90 owing to the circuits 3 and 4 or other arrange- 55 ings, in which ments in the circuit 7, for instance by increasing Figure 1 is a circuit diagram of a transmitting the capacitative reactance of one of these grid t tion, circuits and increasing the inductive reactance of Figure 2 a circuit diagram of a filter circuit the other, and thereby de-tumng the valve 01 to 55 or tificial line, a shorter wave and the valve 02 to a longer wave, m

the difference or sum of current of the circuits 5 and 6, is obtained. In circuit 5,

Circuit 6,

In this case the modulation could be possible not deep by reason of the elimination of one side band, therefore we can diminish the carrier wave by the addition of a suitable phase of the carrier from D2 through the arrangement 8, which may be made either with an amplifier (valve), as in the scheme 01, or without.

Finally, by adjusting a reverse phase through the arrangement 8 We can eliminate the carrier.

Theone side band modulated output obtained at the points p and q may be amplified and utilized in any manner.

As pointed out above, the most important feature in the arrangement described is a filter circuit which will allow some frequency band to pass with substantially the same phase disp1acement.

For this purpose the most suitable arrangement should be the filter shown in Fig. 2, which should besubstituted for the circuit 1' and F in Figure 1.

a It is known that in an artificial line L (Fig. 2) the resistance R can always be so chosen that no reflected wave can be present in the system. In

this case different phases can be obtained in different parts of the line. 7

By coupling a number of tuned circuits to such an artificial line as shown in Fig. 4 at different points in this line a frequency characteristic like 7 an aperiodic circuit connected to the grid of a valve. 7 What I claim is:-

1. A high-frequency radio transmitter for the transmission of one side band, comprising a source of audio-frequency oscillations, a first modulator of the unbalancedtype adapted to modulate a first; carrier wave by means of audio-frequency V oscillations from the said source, a filter adapted to pass one side band of the wave modulated by the first modulator, means for adding a phaseshifted carrier wave to the filtered wave, means for so demodulating the resulting Wave that after demodulation modulating frequencies appear, but phase-shifted, two second modulators, in which two phases of a second carrier, differing in phase from one another by ninety degrees, are modulated by modulating frequencies also difiering in phase from. one another by ninety degrees, one of the said second modulators receiving its modulating frequency directly from the same source as the first modulator, and the other second modulator receiving a phase-shifted modulating'frequency from the demodulating means, and a difierential output circuit for utilizing the waves modulated by the two second modulators.

2. A high-frequency radio transmitter as claimed in claim'l, further comprising means for adding some phase and amplitude of the second carrier to the final product in the difierential output circuit.

JOZEF PLEBANSKL

Images