US2025610A

US2025610A - Frequency multiplication system

Info

Publication number: US2025610A
Application number: US743698A
Authority: US
Inventors: Plebanski Josef
Original assignee: Radio Patents Corp
Current assignee: Radio Patents Corp
Priority date: 1931-07-10
Filing date: 1934-09-12
Publication date: 1935-12-24
Anticipated expiration: 1952-12-24
Also published as: DE616900C

Description

Dec. 24, 1935. J. PLEBANSKI FREQUENCY MUL TIPLICATION SYSTEM Filed Sept. 12, 1934 5 Sheets-Sheet 1 INVENTOR ATTORNEY Dec. 24, 1935.

J. PLEBANSKI FREQUENCY MULTIPLICATION SYSTEM Filed Sept. 12, 1934 3 Sheets-Sheet 2 INVENTOR JOSE? PLEBANSM BY %f/%hx ATTORNEY Dec. 24, 1935. J. PLEBANSKI 2,025,610

FREQUENCY MULTIPLICATION SYSTEM Filed Sept. 12, 1954 r L 3 Sheets-$heet 5 INVENTOR IOSEF PLEBAN5K\ ATTORNEY Patented Dec. 24, 1935 UNITED STATES TDAENT OFFICE FREQUENCY MULTIPLICATION SYSTEM Application September 12, 1934, Serial No. 743,698 In Poland July 10, 1931 12 Claims.

My invention relates to improvements in radio systems and method of operation, and has for its main object to provide a new method and means for frequency multiplication.

In many cases, it is desirable to operate with a relatively low frequency in one part of a radio system, such as a transmitter or receiver and to use relatively higher frequencies in other parts of the system. This necessitates the provision of frequency multiplying means between the different portions of the system. An example of this occurs in single side-band transmission systems. The advantages of single side-band transmission with or without carrier suppression are well known. A substantial saving in transmitting power obtained through the suppression of the other side-band with or without the carrier frequency is elfected.

A condition, however, encountered in transmission systems of this type is the fact that the suppression of the other side-band can be effectively carried out with low frequencies only, such as of the order of about twenty kilocycles for which filters with a sharp cut-oif characteristic can be constructed. When starting with a low carrier frequency of the above order, it is necessary to increase the frequency to a higher carrier frequency by means of a frequency multiplication arrangement. In using the commonly known frequency multiplication systems such for example as one involving a non-linear characteristic vacuum tube for distorting the wave shape from which the desired high frequency is segregated by suitable filter means, great difiiculties are encountered due to undesired cross modulation produced between the side-band frequencies of the modulated carrier. This results in substantial distortion and interference of the signals being transmitted.

Accordingly, an object of my invention is to provide a new method of and means for multiplying a given, and particularly a modulated, frequency without inducing interaction or cross modulation between the side-band frequencies.

Another object of the invention consists in providing an improved and simplified system for single side-band transmission with or without carrier frequency suppression and which is substantially free from distortion and similar objectionable interference inherent in systems of similar nature.

A further object of the invention consists in providing a new method of transmitting and reconstructing a carrier frequency for single sideband transmission systems to substantially reduce,

fading and similar objectionable phenomena. The invention has other objects in view which will appear hereinafter in a detailed description thereof in connection with the accompanying drawings in which:

Figures 1 and 2 are schematic diagrams illustrating the novel method and principle of frequency multiplication embodied in the invention. Figure 3 shows one practical arrangement for carrying out the invention.

Figure 4 illustrates the response characteristic of a filter adapted for single side-band systems.

Figure 5 illustrates a modified circuit arrangement embodying the novel method of frequency multiplication as applied to single side-band transmission.

Figure 6 illustrates a modification of the circuit shown in Figures 3 and 5.

Figure 7 is a circuit diagram for receiving a single side-band transmission with auxiliary side frequencies for reconstructing the carrier frequency;

Figures 7a and 7b illustrate response characteristics explanatory of the operation of the circuit of Figure 7 and Figure 8 illustrates a further modification of the system shown in Figure 3.

The novel method of frequency multiplication according to my invention involves the use n is the carrier frequency in a radio transmission A1 sin W1t+A2 sin W2t= cos (W1-- W2) t in which w1= 271'fh and w2=21rfs.

V. manner, a modulated frequency 21% is obtained which in turn is combined by means of a further In this manner the frequency is is transformed in the modulators M1 and M1 into its combination frequencies n+1, and fhfs of which the latter. is segregated by suitable resonant means in the modulator M1 and the former is segregated in the'modulator M1. The thus obtained combination frequencies fh-i-fs and fh-fs are then'in turn combined as shown in the second modulator M2 thus yielding a combination frequency ,fs+fh+fsfn=2fs; that is, double the original or carrier frequency f5. The double frequency 2fs thus obtained is then combined with the auxiliary frequency is by means of a pair of further modulators M3 and M3 in a similar manner as previously described to produce side frequencies 2fs+fn and 2fsfn yielding a further combination frequency equal to 4fs produced by the modulator M4. In this manner, as will be understood from Fig. 1, any harmonic of the series 2" .fs of the original or signalling frequency may be obtained and applied to a utilization circuit such as an amplifier transmission line or wireless antenna.

In Figure 2 I have shown a schematic arrangement similar to Figure 1 for the multiplication of a modulated carrier fs specifically used in a singleside-band transmission system for suppressing the side-band by means of a filter in the low frequency stage. For this purpose I have shown modulators m, ml, m2, m3, m4 mn, illustrated by cross-hatched rectangles carrying the modulated frequency currents, while the over the line I to the modulator m-which is furthermore supplied with the frequency is. In

this manner a modulated carrier is obtained which is combined in a further modulator m1 with the auxiliary frequency in, thus yielding modulated intermediary frequencies fs-fh. and fs+fh. At this stage, one of the side-bands 'may be suppressed, such as by means of a sharp cut-off filter having a characteristic as shown "in Figure 4. At the same time, the carrier may also be suppressed by the proper design of the filter to encompass both one side-band and the carrier frequency as is understood. The modulating intermediary frequency fs-fh is then combined by means of a further modulator with an unmodulated intermediary frequency fs+.fh supplied from the modulator M1 as shown. In this modulator m3 with the auxiliary frequency In yielding a second intermediary modulated frequency 2fs--fh, which latter is in its turn combined in a further modulator 1m with the unmodulated, obtainedwhich may be combined in a common output for suppression of the carrier or, if the carrier has been previously suppressed.

for restoration of the carrier in the common. out:

supplied'from a suitable source IE to the power amplifier 3 by means of a high frequency transformer 4. The modulation shown is the well known anode current or Heising modulation. For this purpose the output of the amplifier tube is directly connected to the anode of the power amplifier tube 3 whereby the high frequency currents in the output of the tube are modulated in accordance with the low frequency or modulating currents. From the output of tube 3, the modulated high frequency s is applied to the input of a modulator amplifier or frequency converter tube 6. through transformer 5. In addition currents of the auxiliary frequency in produced by a generator IT are applied to the modulator amplifier tube 6 as shown, resulting in the production of combination intermediary frequencies in the output of tube 6 of which the component fwfh is segregated by means of a filter F which may have a characteristic as shown in Figure 4 and may be designed to simultaneously suppress the carrier frequency as pointed out before. The thus obtained modulated first intermediary frequency is then applied to a further modulating tube 1 for combination with the unmodulated intermediary frequency fH-fn supplied from the tube 9 of the unmodulated multiplier system to the anode of the tube! in Heising modulation arrangement.

The unmodulated intermediary frequencies are produced by means of a pair of modulator-converter tubes 8 and I2 with input circuits supplied with the carrier frequency is through transformers l0 and II, respectively, and with the frequency In directly applied to the input circuits of tube-s 8 and 12 as shown. In this manner combination frequencies fs+fn and fs-fh are produced'in the output circuits of tubes '8 and I2, respectively, of which the former is segregated in the output of tube 8 and the latter is segregated in the output of tube I2 by suitable resonant means. The single intermediaries thus obtained are then applied through transformers l4 and [5, respectively, to the input of a pair of further tubes 9 and [3 whose anodes are connected for mutual modulation producing an unmodulated frequency 2fs in their common output circuits connected throughtransformers I8 and IS with the anode circuits of tubes 9 and I3, respectively. The modulated and unmodulated double frequency 2fs thus obtained may be further mutually combined with the: auxiliary frequency in in a similar manner to produce any desired mul- I tiple according'to the series 2% as explained in connection with the schematic showing in Fig- 6 ure 2. 20 and 2| are coupling coils connecting the output of

tubes

1 and 9 to a common output circuit carrying the, double carrier frequency 2h Figure 5 shows a modification of the circuit of Fig. 3 using a return or reflex arrangement from a stage carrying a multiplied frequency to the input circuit of the initial frequency current resulting. in a great simplification of the circuit.

'As shown, an audio-transformer l controls the speech amplifying tube 2 serving to modulate the power amplifier 3 controlled. by carrier frequency is. The modulated carrier is applied to the input of a modulator amplifier 6 which is also controlled by the auxiliary frequency in, thus yielding a one side-band modulated intermediary frequency fs-fh by the further use of a suitable filter in a manner similar to that described in connection with Fig. 3. This latter is applied to the input of a further modulator tube 1 together with a non-modulated intermediary frequency fs+fh supplied through a transformer 32 from the unmodulated carrier multiplication system. In this manner a modulated double carrier frequency 21% is obtained in the output of the tube 1 which is applied to the input of a further modulator amplifier tube 24 together with the auxiliary fa resulting in a combination frequency 2fsfh in the output of tube 24, which latter is in turn applied to the input of modulator amplifier 35 together with a non-modulated second intermediary frequency Zfs-I-fh supplied through transformer 29 from the unmodulated carrier system. In this manner, a modulated four-fold carrier 4fs is secured in the output of tube 35 which by means of a transformer 36 may be combined with the non-modulated carrier 4J5 as shown supplied by the transformer 33 either for suppressing or restoring the carrier.

The non-modulated multiplication system comprises a first modulator tube 26 having its input controlled by both carrier frequency f5 and auxiliary frequency fh, thus yielding two combination frequencies fs-fh and fs+fh which are both segregated by means of resonant circuits inserted in the output circuit of the tube and in turn combined in the input of a modulator tube 37 through

coupling transformers

36 and 3! respectively. The resonant circuit carrying the frequency fs+fh is furthermore coupled to the input of the tube 1 through transformer 32 as described before, to combine with the signal modulated intermediary fsfa for securing a modulated carrier 2fs in the output of the tube 1. By combination of the intermediary frequency fsh and ,fs-l-J'h by tube 31, a non-modulated double carrier frequency is secured in the output of the tube 31 which is returned or refiexed through transformers 34 and 35- to the input of the first modulator tube thus combining with the auxiliary frequency ft and producing further intermediate frequencies 2fs-fh and 2fs+fh in the output circuit of the tube 26, which are segregated by means of suitableresonant circuits as shown and applied through transformers 21' and 28, respectively, to the input'of a modulator tube 38 for combination to yield a fourfold unmodulated carrier 4J5 in its output circuit which as described may be combined with the modulated four-fold carrier as shown. The intermediate frequency 2fs+fh is furthermore applied through transformer 29 to the: input of the tube 35 for combination with the signal modulated intermediary frequency 2fsfh as described hereinbefo-re. Otherwise the circuit and. its operation is similar to that described in connection with Figure 3.

Figure 6 shows a circuit arrangement similar to Figure 5 for multiplication of the initial frequency to its sixteenth harmonic. In place of vacuum tube modulators for changing of the frequency, I have shown rectifiers, such as dry rectifiers or crystal rectifiers or the like arranged in a well known bridge circuit. In this manner the entire circuit is greatly simplified and both the installation and maintenance costs greatly reduced. As is obvious, the generators I6 and I! for the carrier frequency and the auxiliary frequency in this case must be designed for increased power or provided with suitable amplifiers. The circuit according to Figure 6 also utilizes the reurn or reflex principle as will be described in detail.

This circuit also substantially comprises a first system for multiplying the signal modulated carrier and a second system for multiplying the unmodulated or pure carrier and mutual circuit connections for combining modulated intermediary frequencies with unmodulated intermediary frequencies in a manner similar as described before to secure a final multipled output frequencyof a desired order free from distortion and. similar eifects inherent in systems heretofore known in the art.

Referring to the circuit arrangement of Figure 6, I have shown an input transformer I for applying the modulating, such as audio frequency currents supplied from a microphone or the like to a first modulating circuit 40 including a rectifier arrangement 4| comprising four rectifier elements such as dry or contact rectifiers connected in the well-known bridge circuit as shown. The circuit 4!) furthermore is supplied with carrier frequency currents applied through transformer 45 from a circuit including the carrier frequency generator I6. In this manner a modulated carrier Mm) is obtained and applied to an intermediate or filter circuit 42 of known design. From the circuit 42 the modulated carrier is applied to a further modulating circuit 43 including a rectifier arrangement 44 and supplied with auxiliary frequency currents supplied through transformer 10 from a circuit including the auxiliary frequency generator l1. manner a first intermediary signal modulated frequency is obtained of which one side-band (such as fs-l-fh in the example shown) with or without the carrier may be suppressed such as by means of a suitable filter :35 as shown. This frequency is then applied to a modulating circuit 41 including a rectifier arrangement 48 and also carrying currents of the unmodulated intermediary frequency is-l-fh supplied from the un modulated multiplication system through transformer 8%. In this manner a. multiple modulated carrier frequency 2fs(m) is produced in the circuit 4-"! and its associate filter circuit 49. The frequency 2mm) is then applied to the modulation circuit 59 including a rectifying arrangement 5| and also carrying currents of the auxiliary frequency in applied through transformer 1| connected in the auxiliary frequency circuit of the generator ll.

mediate resonant circuit 53 is applied to a further modulation circuit 54 including a'rectifying arrangement 55 and also carrying currents of thesecond unmodulated intermediary frequency I 2fs+fh supplied from the unmodulated multiply- The result- In this The resulting combination frequency 2fs-fh(m) after passing through inter- (iii ' iliary generator l1.

idiary circuit 59 is then combined in circuit 60 including rectifying'arrangement 6| with a nonmodulated intermediary 4f8+fn supplied from the unmodulated multiplier through transformer 8| as shown. In this manner a modulated frequency 8fs(m) is obtained, which afterpassing through intermediary circuit 62 is combined in a further modulation circuit 63 including a rectifying arrangement 64 with the auxiliary frequency in applied to the circuit through transformer 13 from the circuit ofthe auxiliary generator IT. The resulting modulated intermediary frequency 8js-fh(m) after passing through intermediate circuit 65 is then combined in the modulation circuit 66 including rectifying arrangement Bl with the unmodulated intermediary 8fs+fh supplied from the unmodulated multiplier through transformer 95. From this there results a final'modulated carrier 16mm) applied to the I A A sin W11 A2 sin Wat 2 intermediate circuit 68 and which may be comlated frequency 16f5 in the intermediate circuit I00 which may be combined with the signal modulated frequency 1675 as described.

In the arrangements according to Figures 5, 6

and 8, the desired beat or combination frequencies are segregated by means of resonant circuits, It is understood that any other segregating means or filters such as piezo crystals or the like with or without associated amplifiers may be provided for this purpose. It is furthermore understood that the reflex arrangement may be employed repeatedly, resulting in a further simplification of the circuit arrangement as is obvious.

An arrangement as shown in Figure 6 using rectifiers such as dry rectifiers, diodes, etc., has the great advantage that the modulation of the frequency ,fs by the frequency in or its harmonics 211.13 is linear; that is, the modulation conforms a general to the formula:

When vacuum tubes are used for the transposing of the frequencies with non-linear characteristics, the modulation conforms to the formula:

pression or restoration of the carrier as described before in a common output circuit to be connected to terminals a and b.

The unmodulated carrier multiplier is comprised of a first modulator circuit 18' including a rectifier arrangement 83 and supplied with the carrier frequency is through transformer 18 and with the auxiliary frequency in through transformer T4. The resulting combination frequencies ,fs+fh and ,fsfn are segregated by means of intermediary circuits coupled through

transformers

83 and 82, respectively, and combined in a modulating circuit 81 including a rectifying arrangement 88, thus yielding a frequency 2js in the associated intermediate circuit 90. The frequency 2fs is then applied from the circuit 90 to a modulating circuit 90 including a rectifying arrangement 82 and also carrying currents of the auxiliary frequency is supplied through transformer 15 connected in the circuit of the aux- V The resulting combination frequencies 2fs+fh and 2,fsfh are segregated by means of intermediate resonant circuits. coupled through transformers 92 and 96, respectively, and

' then combined in a modulation circuit I02 including a rectifying arrangement I03.

The resulting frequency 4fs produced in the circuit I02 is returned or fed back in a reflex arrangement to the first modulation circuit 18' through transformers I04 and I05 where it is combined, with the auxiliary frequency In, yielding intermediate frequencies 4fs+fh and 4fsfh which are segregated by means of resonant intermediate circuits coupled to the circuit 18" through transof intermediate circuits coupled to the

transformers

94 and 93 and in their turn combined in 'a modulation circuit H19 including a rectifying From the last two members of the formula, it is seen that frequencies 2w1t and 2wzt are produced and in addition there will be higher harmonies of these frequencies which may cause interference and distortion of the signals being transmitted. The circuit according to Figure 6 is free from this disadvantage as already pointed out.

The arrangements according to Figures 2, 3, 5 and 6 can be further simplified where it is required to suppress one side-band and the carrier frequency. A simplified arrangement of this is shown by Figure 8 which merely differs from Figure 2 by the employment of harmonic frequencies of the auxiliary generator I1 such as the harmonic 2fh used for heating with the modulated multiplied freqency 21% as shown, otherwise the circuit is similar in design and function to previous circuits as will be understood.

Referring to Figure 7, this shows a receiving system especially adapted therewith in connection with the invention and for communication with a single side-band and elimination of the carrier frequency. As iswell known in systems of this type, means must be provided at the receiver for restoring the carrier necessary for reproducing the original signals.

In order to restore the carrier at the receiver 'means known in the art. In addition to this sin- 1 'gle side-band, two further side-bands or side frequencies are produced, for instance, by modulation according to a single not outside of the regular modulation band such as of 6000 cycles in the above example. Such pilot bands or frequencies may easily be obtained by modulating the carrier in the final stage with a frequency of 6000 cycles and combining it with the m0dulated frequency in such a manner that the carrier itself is suppressed; Any suitable means known in the art may be provided for this purpose, such as a balanced modulator and the like. Thus, two pilot frequencies or side-bands are obtained produced by the oscillations of 6000 cycles and a single modulated side-band produced by the signalling modulation and comprising 30 to 4000 cycles.

At the receiver the modulated side-band of 30 to 4000 cycles is received by a suitable filter F2 having a response characteristic as shown in Figure 7 b and applied either directly or through any suitable frequency changing means to the detector tube II6 for reception by a translating means such as loud speaker H with interposed amplifier well known in the art. The side frequencies produced by the oscillations of 6000 cycles are passed through filter F1 having a response characteristic as shown in Figure 7a, and applied to a frequency doubling tube III or any other arrangement for doubling the frequency. In this manner the carrier wave of double frequency is restored in accordance with the equa tion:

This pilot frequency is then utilized for controlling an oscillator H2 having a frequency of Z =WL The frequency of the oscillator is applied to the detector tube I I6, thus restoring the original carrier frequency for de-modulation and reception of the signal. In place of a single pilot frequency, such as 6000 cycles as in the example given, it is understood that a band of pilot frequencies may be provided and transmitted.

The above method of transmitting the carrier frequencies by means of its side-bands involves the great advantage of reducing the effects produced by fading, especially so-called selective fadings. The arrangement according to Fig. '7 may be furthermore modified by doubling the single modulated side-band passed through the filter F2 by means of a frequency doubling arrangement such as of the type described hereinbefore and shown for instance by Fig. 3, and then to combine the doubled carrier frequency produced by the frequency doubling tube I I I. In the latter case an additional auxiliary oscillator will be necessary as shown at fh. I have furthermore shown at I II! an input amplifier and an antenna I I3 with ground connection H4.

While the invention has been described with specific reference to the showing of the drawings, I desire it to be understood that various modifications may be made and that no limitations upon the invention are intended short of its broad and underlying spirit as expressed in the appended claims.

I claim:

1. The method of frequency multiplication consisting in combining a fundamental frequency wave with an auxiliary frequency wave to derive sum and difference combination frequency waves, combining said combination frequency waves to derive a further combination frequency wave therefrom equal to the second harmonic of said fundamental frequency Wave, combining said second harmonic frequency wave with said auxiliary frequency wave to derive secondary sum and difference combination frequency waves therefrom, and combining said secondary combination frequency waves to produce a further combination frequency wave equal to four times the frequency of said fundamental frequency wave and successively continuing the process until obtaining a final desired harmonic frequency wave of the order 2 of the fundamental frequency.

2. The method of frequency multiplication consisting in combining a fundamental signal modulated carrier frequency wave with an auxiliary frequency Wave to derive therefrom sum and difference combination frequency waves, producing similar combination sum and difference frequency waves from an umnodulated fundamental carrier frequency wave and said auxiliary frequency wave, and combining a combination frequency wave derived from the modulated carrier with a combination frequency wave derived from the unmodulated carrier to produce a modulated second harmonic of said carrier frequency wave.

3. The method of frequency multiplication consisting in beating a fundamental frequency signal modulated wave with an auxiliary frequency wave to derive therefrom sum and difference combination frequency waves, producing similar sum and difference combination frequency waves by beating an unmodulated fundamental wave of the same frequency as said fundamental signal modulated wave together with said auxiliary frequency wave, combining a combination frequency wave derived from said modulated fundamental frequency wave with a com,- bination frequency wave derived from said unmodulated fundamental frequency to produce a modulated second harmonic of said fundamental frequency wave, producing a second harmonic of said unmodulated fundamental frequency wave, combining said second harmonic modulated fundamental frequency wave with said auxiliary frequency wave to derive secondary sum and difference combination frequency waves therefrom, producing similar secondary combination frequency waves by beating together said second harmonic unmodulated carrier frequency wave and said auxiliary frequency wave and combining a secondary combination frequency wave derived from said modulated second harmonic wave with a combination frequency derived from said unmodulated second harmonic wave to produce therefrom a modulated fourth harmonic of said fundamental frequency wave and continuing the process by producing further successive harmonies of said unmodulated fundamental frequency Wave of like order supplied by said first said auxiliary frequency wave to derive combination frequency waves of the respective orders and combining said fourth harmonic modulated carrier wave with said auxiliary frequency wavei and beating a resultant combination frequency wave with a corresponding combination frequency wave of like harmonic order of the unmodulated fundamental frequency wave to produce an 8th harmonic'modulated wave of said fundamental frequency wave and analogously continuing the process until obtaining a desired modulated harmonic wave of the 2 th order of said fundamental frequency wave.

4. The method of frequency multiplication as claimed in claim 3 in which said further harmonies of said unmodulated carrier frequency wave are produced by combining combination frequency waves derived therefrom by heating with said auxiliary frequency wave.

5. In a method of frequency multiplication as claimed in claim 3 including suppressing the carrier frequency component of the initial fundamental modulated carrier frequency wave and re- 7 introducing acarrier in the final stageobtained from multiplication of the unmodulated initial carrier wave frequency wave having the frequency necessary for said re-introduction to produce an output signal with a carrier component.

6. The method of frequency multiplication as claimed in claim 3 including suppressing one sideband of the initial fundamental modulated carrier frequency wave and suppressing the carrier frequency component in the final stage by combination with the multiplied unmodulated carrierwave having the same frequency .as said carrier frequency.

'7. A frequency changing system comprising a source for producing a fundamental carrier frequency wave, a further source for producing an auxiliary frequency wave, means for combining said frequency waves to derive sum and differcombination frequency waves, further means for beating said combination frequency waves to derive a second harmonic of said fundamental frequency wave, and means for beating said harmonic frequency wave with said auxi1- iary frequency wave and beating resultant combination frequency waves to produce the fourth harmonic wave of the fundamental frequency wave and continuing the process of producing harmonic waves by beating with said auxiliary frequency wave and beating together resultant combination frequency waves substantially as described until obtaining a final desired harmonic wave of the 2 th order of the said fundamental frequency wave.

8. A frequency changing system comprising a source for producing a fundamental carrier frequencywave, a further source for producing an auxiliary frequency wave, a first mixing circuit for combining said carrier frequency wave and said auxiliary frequency wave to derive sum and difference combination frequency waves, a sec' ond mixing circuit for combining said combination frequency waves to derive a second har monic beat frequency wave of said fundamental, a third mixing circuit for beating said second harmonic frequency wave with said auxiliary frequency wave to derive secondary combination frequency waves, a fourth mixing circuit for combining said secondary combination frequency waves to derive therefrom a fourth harmonic .wave of said fundamental, and further mixing circuits for producing higher harmonics of said fundamental frequency according to the series 2 until obtaining a desired fourth final harmonic frequency'wave of desired order.

9. In a frequency changing system as claimed in claim 7, including means for feeding currents from a circuit carrying a wave. of higher harmonic order to a circuit carrying a wave of lower harmonic order for producing combination frequencies between said currents and said auxiliary frequency wave in the mixing circuit for said lower harmonic frequency wave.

.10. A frequency changing system comprising a source for producing a fundamental carrier frequency wave; means for modulating said carrier frequency in accordance with signal variations; a source for producing an auxiliary frequency wave; means for deriving an unmodulated component of said carrier frequency wave; a first multiplication system for increasing said unmodulated carrier component comprising first heterodyning means for combining one unmodulated carrier with said auxiliary frequency wave to derive a combination frequency wave further heterodyning means for combining said combination frequency wave to derive a second harmonic carrier frequency wave, further heterodyning means for combining said second harmonic carrier frequency wave with said auxiliary frequency wave for producing combination frequency wave, means for heterodyning said latter combination frequency wave to produce a fourth harmonic of said carrier frequency wave, and means for alternately heterodyning harmonic frequency wave of said carrier with said auxiliary frequency wave and for mutually heterodyning the resultant combination frequency wave to produce a final desired harmonic of the 2 order of said unmodulated carrier frequency wave; and a second multiplication system for increasing said modulated carrier component com-.

prising first mixing means for combining the modulated fundamental carrier frequency wave with said auxiliary frequency wave to derive combination frequency wave; further mixing means for combining one of the latter combination frequency wave with a combination frequency wave of like order of said unmodulated carrier component supplied by said first multiplication system to produce amodulated second harmonic carrier frequency wave; additional mixing means for combining said modulated second harmonic carrier frequency wave with said auxiliary frequency wave to derive combination frequency Wave therefrom; further mixing means for combining one of said latter combination frequency wave with a corresponding combination frequency wave of like order supplied by said first multiplication system for producing a modulated fourth harmonic carrier frequency wave; and additional means for alternately heterodyning modulated harmonics of said carrier frequency Wave with said auxiliary frequency wave and heterodyning resultant combination frequency wave of the modulated carrier frequency wave with a corresponding combination frequency wave of like order of the unmodulated carrier frequency wave supplied by said first multiplication system to secure a final modulated carrier of the 2 order of the fundamental carrier frequency wave.

11. A frequency changing system as described in claim 10 for single side-band transmission I