Oct. 14, 1969 c. BABILLOn 3,473,125 KLYSTRON AM TRANSMITTERS Original Filled Dec. 1, 1964 4. Sheets-Sheet sHEATING SOURCE CUR - WOTAGE - SOURCE 8 2 M ),A. 20 f O 4 BEAM MODULATOR VOLTAGE WOAGE SOURCE SOURCE -- ar FIG. f. Oct. 14, 1969 C. BABILLON 3,473,125 KLYSTRON AM TRANSMITTERS Original Filed Dec. 1, 1964 4 Sheets-Sheet 2 Ic/ICO Fig. 3 Va/Vc FIG.2 Oct. 14, 1969 c. babillon 3,473,125 KLYSTRON AM TRANSMITTERS Original Filled Dec. 1, 1964 4. Sheets-Sheet 5 & N. Oct. 14, 1969 c. BABILLON 3,473,125 KLYSTRON AMTRANSMITTERS Original Filled Dec. 1, 1964 4. Sheets-Sheet 4 us/uso F. G.6 3,473,125 United States Patent Office Patented Oct. 14, 1969 1. 2 multiple cavity klystron, this klystron receiving a high 3,473,125 frequency signal consisting of a pure sinusoidal oscilla KLYSTRON AM TRANSMITTERS tion. Claude Babillon, Paris, France, assignor to CSF-Com FIG. 1 shows schematically a multiple cavity klystron pagnie Generale de Telegraphie Sans Fil, a corporation of France 20, for example of F2008 type. The diagram shows only Continuation of application Ser. No. 414,968, Dec. 1, these elements which are necessary for a proper under 1964. This application Dec. 19, 1967, Ser. No. 694,962 standing of the invention; for example, the envelope which int, C. H04b I/04 maintains the arrangement in a high vacuum is omitted. U.S. C. 325-120 4 Claims A cathode is heated by a filament 7 supplied from a O Supply source 1. The klystron also comprises a control electrode 8 and an electrode 9, generally known as modu ABSTRACT OF THE DISCLOSURE lation anode. A multiple cavity klystron AM transmitter having a The path of the beam further comprises a duct A-A signal input connected to parallel amplifiers, one being which passes through four successive cavities 11 to 4, linear and the other being non-linear. An exciter stage 5 the first three of which may include damping arrange is connected between the linear amplifier and the input ments 15 to 17. to the klystron and the non-linear amplifier is connected The first cavity has an input 10 to which the klystron to the klystron modulation anode. The non-linear ampli high-frequency input signals is applied. fier passes only the positive signals thereby reducing cur The last cavity 14 possesses an output i8 which is the 20 klystron output. rent consumption and a negative feedback loop connects The collector is shown at 6. the output of the klystron through a detector to the A power supply 3, with its negative pole connected to input of the linear amplifier for retaining, in the low fre cathode 19, and with its positive pole connected to the quency band to be transmitted, suitable phase between the output of duct A-A and to collector 6 is the high voltage klystron modulation signal and the modulation of the 25 supply of the klystron. exciter stage. An auxiliary source 2, with its positive pole connected to the negative pole of source 3 and with its negative This application is a continuation of the application pole connected to the control electrode 8, applies to the Ser. No. 414,968, filed Dec. 1, 1964, now abandoned. latter a bias which is negative with respect to cathode 9. The present invention relates to multiple cavity klystron 30 A bias source 5 has its positive pole connected to AM transmitters. It has for its object to provide an im collector 6 and to the positive pole of Source 3, and has proved transmitter of this type, wherein, by means of a its negative pole connected to a modulator 4, whose out double modulation, which does not raise difficulties as to put is connected, to anode 9. the phase relations to be maintained, it is possible to avoid Except for the supply source of the modulation anode, both the poor efficiency of the klystron operated as a 35 this circuit is the conventional circuit of a klystron am constant intensity beam amplifier for an AM wave, and plifier for high-frequency amplitude modulated signals. the drawbacks inherent to its use as a modulated amplifier In this latter circuit the modulation anode is connected for a sinusoidal oscillation at the transmitting frequency. to the positive pole of source 3 through a simple resist According to the invention, there is provided an ampli ance. The high-frequency amplitude modulated signal is tude modulation transmitter comprising: a general input applied to input 10, and the amplified signal is collected for receiving the signals carrying the information to be at output 18. transmitted; a first and a second amplifier having respec In order to explain the poor efficiency of the klystron tive inputs coupled to the general input, said first ampli used as an amplifier with a constant intensity beam, the fier being a linear amplifier and said second amplifier case of a sound transmitter modulated in amplitude at being a non linear amplifier amplifying only the crests, 100% maximum depth of modulation will be considered above a predetermined level, of the input signal; an os by way of example. FIG. 4 shows one embodiment of an ultra high fre If the klystron is used in this way, it operates as a quency; amplitude-modulating means having a carrier class A amplifier, with a constant collector current ic, input coupled to said oscillator and a modulation input for all input signal levels. Calling Vic the voltage of source coupled to the output of said first amplifier; a multiple 50 3, the power applied to the klystron is Vc.Ic, and the cavity klystron having a radio frequency input coupled ratio of the output power to the power applied to the to the output of said amplitude modulating means and a beam if it is, for example, 40% for the peak output beam intensity modulating electrode coupled to the out power, drops to 10% for the carrier power. Since the put of said second amplifier; and an envelope negative mean statistical depth of modulation is evaluated at 30%, feedback path coupling the output of said klystron to the the mean transmitted power is little different from the input of a stage of said linear amplifier. carrier power and efficiency is very poor. The invention and its advantages will be better under Using the klystron as a modulated amplifier, with the stood and other characteristics will become apparent from modulation applied to the modulation anode in order to the following description and accompanying drawings, in vary the beam intensity as a function of the low-fre which: 60 quency modulating signal, permits varying the applied FIG. 1 is a diagram of a circuit for amplitude modulat power with the level of the transmitted modulating sig ing the beam current of a multiple cavity klystron; nail, so improving the efficiency. FIGS. 2 and 3 are characteristic curves which show In the circuit diagram of FIG. 1, a high-frequency sig the mode of operation of the circuit of FIG. 1; nal is applied to input 10, this signal consisting of a pure FIG. 4 shows one embodiment of an ultra high fre 65 sinusoidal oscillation whose amplitude is so chosen that quency transmitter using a multiple cavity klystron where saturation of the output power is reached at peaks of the in klystron current modulation is Superimposed on the signal applied to the modulation anode. modulation of the input UHF signal; and Under these conditions the tube's modulation charac FIGS. 5 and 6 show characteristic curves which ex teristic has the general shape shown in FIG. 2, where the plain the mode of operation of the transmitter of FIG. 4. 70 abscissae are the ratio Va/Vc, the ordinates being the ratio A preliminary description will be given by means of Us/Uso: Vc is the voltage of source 3; Va is the potential FIG. 1 of an amplitude modulation arrangement for a difference between the modulation anode 9 and cathode 3,473,125 3. 4 19; Va=Vc-Vp--Vn, where Vm is the voltage supplied input signal remains under a certain level as shown in by element 4, and Vc and Cp are the absolute values of FIG. 5, where the abscissae are the amplitude Ue of the the voltages supplied by sources 3 and 5 respectively; Us input UHF signal and the ordinates are the ratio Us/Uso is the output amplitude, and Uso is the peak output am defined above. But, at the peaks, the klystron tends to plitude. compress the modulation. Since modulation is applied The carrier amplitude in the present example corre 5 simultaneously on two stages at the peaks, some com sponds to Us/Uso-0.5. pensation is secured. The overall modulation character The modulation anode voltage Va corresponding to istic has the shape shown in FIG. 6, where the abscissae the carrier is about 0.5 times the voltage Vc. For this are the low-frequency signal S supplied by circuit 28, voltage, the beam current Ic is approximately equal to 0 and the ordinates are the ratio Us/Uso. 0.35 times the maximum current, as can be seen from So this improvement essentially reduces the klystron the curve of FIG. 3 where the abscissae are the ratio modulation voltage with no loss either in efficiency or in Va/Vc and the ordinates are the ratio Ic/Ico, Ico being linearity. the collector current obtained at Va/Vc=1. This curve However, envelope negative feed-back is always essen corresponds approximately to the function tial in order to secure desirable quality, and further diffi culties might arise on account of the high load impedance Ic/Ico-Va3/2/Vc of the klystron modulator.