FI77341C - Method of transmitting signals using the narrowband can. - Google Patents

Description

The invention relates to a method for transmitting information-containing signals by radio using a narrowband signal channel. at the transmitting end for mixing unit-15; a signal of a local oscillator of the transmitting head is applied to said mixing unit; in said mixing unit, a mixing result of said information signal and the local oscillator signal is generated, the frequency range of which is substantially lower than the frequency range of the information signal to be transmitted; the scrambling input signal obtained in the above-mentioned manner is used as a modulation signal of the radio transmitter; and at the receiving end of the transmission system, the detected modulation to be transmitted is separated by a bandpass filter or the like, and the signal thus obtained is directed to the mixing unit of the receiving end.

25 In the transmission of radio frequency signals, there are situations in which a signal with too high a frequency in this band should be transmitted on a narrowband channel. Particularly problematic is the transmission of said signal so that the phase information is preserved. This problem has been particularly pronounced in various radio sounding applications in atmospheric wind measurement applications.

The directions and speeds of the winds in the Earth's atmosphere are known in such a way that the movements of a radrosonde lifted by a gas balloon such as a hydrogen or helium balloon and carried by the wind are monitored by some method from Earth 35 and the winds of different layers of the atmosphere are calculated.

77341 1 There are already three different methods for monitoring radlosondel, namely the Omega and Loran C methods and the so-called transponder system. The known Omega navigation method is actually based on the use of radio-5 signals from the global Omega network for ship navigation. The Omega network has eight transmission stations located around the globe operating in the VLF range at frequencies of 10.2 ... 13.6 kHz. Each station has its own 10 s transmission sequence, which they transmit in synchronization with each other.

In the sounding system, the measurement of winds using the Omega system is known, as is known, in that a VLF receiver is placed in the radlosonde, which amplifies the received Omega signals to such an extent that the omega signals can modulate the probe's rado transmitter. The signals transmitted by the probe are received and detected on the ground, and the actual signal processing and the detection and printing of the measurement results are performed.

The winds can be calculated from the Omega signals by comparing the phases of the signals at the different stations with a common reference, and from the changes in these phases, the probe displacements at certain time intervals can be calculated. It should be noted that the measurement of the above lie requires very efficient filtering methods, as the signals are weak and in the band transmitted from the probe, the signals of most Omega stations are below the noise level.

25

The known Loran C wind measurement system utilizes probes and navigation networks that are local and have a range of about 2,000 km. One Loran C network includes 3 ... 5 stations. The operating frequency of networks in the spectral range of a 100 kHz transmission is 90 ... 110 kHz. Wind measurement using the Loran C-30 system is possible with better accuracy than in the Omega system. The transmissions of the stations in one network are synchronized so that the reception time can be determined from the differences in the arrival times of the signals of the different stations, and the wage changes of the probe and the winds can be calculated from the changes in the differences in the arrival times. Even in this known system, it is essential for accurate timing that the mutual phases of the signals of the different stations do not change.

3 77341 1 In the Lora C system, the probe is substantially similar in structure to the probe in the Omega system. The receiver is a bandpass amplifier with a center frequency of 100 kHz and a bandwidth of about 10 kHz. The bandwidth of the transmission is at least more than 2 x 100 kHz. The ground equipment of this system also resembles the 5 Omega system, in which, however, the correlator must be replaced by a Loran C receiver that measures the time differences of the signals of the different stations.

The principle of the prior art transponder system is that the distance of the probe from the ground position is determined by measuring the travel time of the radio signal from the ground 10 to the probe and back. The probe has a special receiver to receive the signal transmitted from the ground. In the relevant in systems, the measurement is made so that the radio wave transmitted from the ground is modulated by a 75 kHz signal, which is expressed in the probe and which in turn modulates the transmission of the probe. The changes in the phase of the 15 said 75 kHz signals passing through the probe are monitored on the ground, from which the changes in the distance of the probe can be calculated.

In the telemetry channel, the frequency of the signal transmitted (Omega, Loran C or transponder) is considerably higher than the k.o. the information sheet width of the signal 20. For example, in an Omega system, the frequency is 13.6 kHz, but the information range is very narrow. frequency environment, in fact, the necessary information is contained in a band of a few Hz. In Loran C, the center frequency is 100 kHz and a 10 kHz band is sufficient to transmit information. In a transponder system, the signal frequency is 75 kHz 25 and a bandwidth of 1 kHz would suffice.

When these signals are normally modulated by a transmitter, either by amplitude, frequency or false modulus, the required radio channel width in each case is at least twice k.o. frequency.

30

The most obvious way to narrow down the required bandwidth is to allocate frequencies. However, it is not a viable option because the signals in the probe may be so noisy that digital splitting is not possible or the signal formanttl (Loran C) is such that splitting does not make sense.

4,774,311 For a prior art related to the invention, reference is made as one example to U.S. Patent 4,349,919.

The use of intermediate frequencies is familiar from the technology of radio receivers; 5 i.e. the signal frequency and the so-called the difference in the pay oscillator frequency. Normally, this separation frequency, i.e. the intermediate frequency contains the initial modulation information and thus the modulation is expressed from this interval frequency.

10 If, in the case of navigation signals, a difference frequency is formed in the probe · this difference frequency as such does not contain the information contained in the signal, because the information is contained in the lie of the original signal. An unknown factor in the difference frequency is the exact frequency of the pay oscillator signal and thus also its instantaneous lie.

15

For example, in the Federal Republic of Germany, radio traffic regulations only allow a channel width of 20 kHz for radio sonar use. However, previously known transmission methods require a bandwidth of at least 27.2 kHz for the Omega signal.

20

It is an object of the present invention to enable the above requirement to be implemented in a wind measurement system based on Omega signals.

In the known transmission of the Loran C signal, a high modulation frequency presents problems because when the frequency modulus satellite is used in reception (ground), the noise density after detection is proportional to the square of the frequency. Thus, by reducing the modulating frequencies, the S / N ratio of the detected signal could be improved. In principle, the sensitivity 30 of the system can then also be improved by narrowing the intermediate frequency band of the receiver. These objects are also intended to be achieved by the present invention.

When using a known transponder system, in some cases it is necessary to store the 75 kHz signal received from the receiver so that the phase information of the signal is not lost, e.g. However, for most recorders that are good enough for this purpose, the upper limit of the playback band is about 20 kHz. The method of the present invention is intended to solve this problem as well.

5

It is an object of the present invention to provide solutions to the problems discussed above.

In order to achieve the above and later objects, the method of the invention is mainly characterized in that both a signal containing information of said modulation signal and sufficiently accurate information on the frequency of the signal of the transmitting end mixing signal , which contains information about the local oscillator frequency and phase of the transmitting end, and that a mixing result corresponding to the original information signal and frequency of the transmitting head is generated from said signals input thereto in the mixing unit of the receiving end.

The present invention can be advantageously applied to radio signal transmissions in which the actual information bandwidth of the signal is smaller than the baseband bandwidth of the transmission channel, but the signal frequency itself is higher.

The principle of the method of the invention is thus to apply scrambling, i.e. frequency conversion, which shifts the signal band down to a suitable frequency in the baseband range and, in addition to this lowered signal band, transfers in one way or another accurate information of the scrambling signal, i.e. the frequency and phase of the local oscillator signal. After reception, 6 77341 1 of the signal corresponding to the original are reconstructed from said signals. Due to the processing, the original and reconstructed signal have a certain false difference, the magnitude of which el must necessarily be known as long as this phase difference remains sufficiently constant in the transponder applications of the invention or sufficiently slow in the Omega and Loran C applications of the invention.

The invention uses a relatively stable oscillator as a wage oscillator, i. within a short time, it is a few ¢ 5 ... 20) periods, the frequency hardly changes. In this case, it is possible to transmit the frequency and phase of the local oscillator signal on the radio channel so that the frequency of the signal is divided by a suitable division ratio (5 to 20) at the transmitting end and multiplied by the same division ratio at the receiving end. This corresponds to a split ratio of N, only every Nth signal change state (i.e. pulse edge) is transmitted, but this sampling frequency is sufficient to reconstruct the original signal with a phase-locked multiplier because the original signal is very stable in frequency, derived from a suitable crystal oscillator.

For transmission, said division is necessary because the frequency of the pay oscillator-20 must be close to the signal frequency itself in order for the frequency of the difference signal to be transmitted to be low. When this separation frequency and split frequency is used in the invention to modulate the transmitter and the linearity of the radio channel is taken care of, it is achieved that the maximum modulating frequency is much lower than the original signal frequency received in the probe 25 and thus the required bandwidth can be reduced. The signals are restored to their original frequency at the receiving end using the methods detailed in this application.

In the following, the invention will be described in detail with reference to some application examples of the invention shown in the figures of the accompanying drawing, to the details of which the invention is in no way narrowly limited.

Figure 1 schematically shows a radlosonde and its application to an Omega wind sounding system.

7 77341 1 Figure 2 schematically shows probe radio systems in the embodiment of Figure 1.

Figure 3 is a block diagram of transmission-5 end systems of a first embodiment of the invention.

Figure 4 illustrates a signal reconstruction procedure in the embodiment of Figure 3.

Fig. S shows another embodiment of the invention using a frequency derived from the reference frequency of a synthesized transmitter as a local oscillator frequency.

Fig. 6 shows a signal reconstruction procedure of the system of Fig. 5.

Figure 7 shows an embodiment of the invention for recording and reconstructing a transponder probe signal, while Figure 7 is a block diagram of a recording system.

20

Fig. 8 shows the same embodiment as Fig. 7 for the signal strip unwinding procedure.

Figure 1 is a schematic block diagram of the operation of the Omega wind probe-25 system. The system includes a radlosonde 10 attached by means of a probe wire 11 to a lighter probe balloon 12 which lifts the probe 10 from the ground to the upper air layers. The probe 10 includes a receiver antenna 14 and a transmitter antenna 15 which transmits a radio signal R to a ground receiving apparatus comprising a receiver-30 and a modulation module 30. The detected modulation is passed to a unit 40 comprising a correlator and other Omega signal filtering and spurious measurement components. A signal is passed from unit 40 to computer 60, which performs the wind calculation. The computer peripherals 60 (shown) perform printing the calculation.

According to Fig. 2, the long-wave Omega signals received by the antenna 14 of the probe 10 are passed to the VLF-Omega receiver 20. The probe 10 35 8 -, „77341 1 also includes a meltarloea 16» from which the measured Mlttarloea 16 measures meteorological quantities, pressure, temperature and relative humidity. The radio transmitter 18 transmits via the transmitter antenna 15 a radio signal R to the ground station equipment 30, 40 and 60 shown in Fig. 1.

If the VLF receiver 20 is an Omega receiver, it may be tuned to only one frequency, e.g., 13.6 kHz. The bandwidth (-3 dB) is e.g.

10 20-500 Hz and gain about 80 dB. The receiver 20 is thus a band-end amplifier. The latest sounding system can utilize more than one Omega network frequency, allowing a more broadband amplifier to be used in probe 10. If el is used for frequency conversion it is possible to transmit lime signals in the range of 10.2 ... 13.5 kHz. When using frequency-15 conversion, only one separation frequency falls on one narrow fixed frequency filter after the mixer. If it is desired to transmit several signals in said frequency range with the method of the present invention, corresponding bandpass filters must be added after the mixer, the output signals of which can be summed for the module. At the receiving end, several parallel reconstruction amplifiers are then required, which can use a payload oscillator signal generated by a single phase lock.

The bandwidth mentioned by way of example above relates to the conventional method in use, but the practical bandwidth range is preferably 300 ... 900 Hz, i.e. 600 + 300 Hz or also 500 Hz, but said 20 Hz el in the probe systems used is not practical. Thus, the Omega receiver may be tuned to only one frequency, e.g., 13.6 kHz, but it is not mandatory. In previously known old systems, it was advantageous to do so in order to avoid interference, but newer systems seek to obtain additional information on the use of several frequencies, thus making the receiver more broadband.

35 In the radio transmission of the probe 10, 18 from the modulation scheme of the above units 16 and 20 and summed and the sum modulates the transmitter 18. The most commonly used modulation method is frequency modulation. The frequency bands 400 ... 406 MHz and 1660 ... 1700 MHz are reserved for sounding use.

Since the baseband modulation signal is 13.6 kHz, the width of the radio frequency-5 channel must be at least 2 x 13.6 kHz 27.2 kHz in order for this Omega signal to be transmitted to the ground station by radio using frequency modulation.

Figure 3 shows an implementation of the Omega receiver 10 of the probe 10 according to the invention, i.e. a preferred VLF receiver 20 of Figure 2. This application example is a single frequency 13.6 kHz receiver 20. The receiver 20 comprises a preamplifier and an antenna adapter 21 with a frequency range preselection. When the center frequency is 13.6 kHz, the bandwidth can be e.g. 500 ... 2000 Hz, which is not critical. A suitable gain is of the order of 15 20 ... 40 dB. According to the invention, the receiver 20 comprises a local oscillator 22 having a frequency of e.g. 12.3 kHz, which is formed by dividing the frequency of a suitable crystal oscillator. The stability el of the crystal oscillator is not necessary, but it eliminates the possibility that the frequency oscillation would cause a phase error and that the difference-20 frequency of the output of the mixer 23 would creep out of the band of the next amplifier. In the mixer 23, the frequency difference frequency of the signal and the local oscillator 22 is formed from 13.6 to 12.3 = 1.3 kHz.

The receiver 20 shown in Figure 3 further comprises a bandpass amplifier 25 for extracting exactly that separation frequency 1.3 kHz from the output of the mixer 23. This system also provides better selectivity than the known method. The receiver 20 also comprises a frequency divider 25, since simply transmitting the difference frequency, i.e. in a way an intermediate frequency, to the ground is not sufficient for the purposes of the invention, because the phase and frequency of the local oscillator 23 are affected by the phase of the mixing result signal 30, and it is practically impossible to place an oscillator mere prior knowledge of its operating frequency would suffice. Therefore, in the system of the invention, real-time information on both the frequency and the false signal of the local oscillator 22 signal is required. In order to transmit this information according to the invention in a narrow channel, the local oscillator signal is divided by the phase information storage interval by a digital frequency divider 25 with a suitable division ratio e.g.

8: 11a to make the frequency modulating the transmitter to be transmitted by radio sufficiently small. Transmitter 20 further comprises a summing unit 26 in which the two separate signals obtained are summed and together and 5 the signal levels and their ratios are set to suit and the transmitter 18 of the probe 10 is modulated with this sum signal + S ^.

Reconstruction of the signal R of the radio transmitter 18 of the probe 10, i.e. return to the original frequency range, takes place according to the invention with the arrangement shown in Fig. 4 10. Since the correlators of unit 40 are designed to handle the original frequencies of the Omega network, the signals must also be restored before being fed to the correlator. The reconstructor poles shown in Figure 4 thus belong to a ground unit 30, which further comprises a detector of the receiver 30.

15

According to Figure 4, the difference modulation frequency 31 kHz and the frequency division result of the local oscillator 22 are separated from the detected modulation received from the receiver of the unit 30 by the bandpass filters 31 and 32. In the phase locked column according to Fig. 4, a signal exactly the same frequency and synchronized with the signal of the initial oscillator 22 of the probe 10 is generated, which is now used as the second input signal of the mixer 33. The phase lock circuit includes a phase detector 34 and a low-pass filter in its block, the output signal of which is a phase difference proportional DC voltage Uq, which controls 25 blocks 36, which is a VCO (Voltage Controlled Oscillator) with a duty frequency of about 12.3 kHz. oscillating and the frequency of which is adjusted by the output voltage U of the phase detector 34 so as to be exactly 8 times the 1.537 kHz signal received from the receiver 30 to the phase detector 34. The second reference signal of phase detector 34 is obtained from the output frequency of the VCO by dividing it by 8 in unit 37. Thus, the 1.537 kHz frequency division result of the pay oscillator 22 is multiplied by 8 so that the result is synchronous with the 12.3 kHz of probe 10. with a signal of frequency n.

According to Fig. 4, the difference and sum frequencies of the 1.3 kHz and 12.3 kHz signals to be mixed are generated in the mixer 23, from which the desired fQ = 13.6 kHz signal is extracted at the last step, i.e. the bandpass amplifier 35. . The selectivity of the bandpass amplifier 35 is arranged so that unnecessary scrambling results are sufficiently attenuated, e.g., 30 dB training at 1 kHz from 13.6 kHz is sufficient. The gain of the amplifier 35 is set such that the output signal f is at a suitable level to be fed to the correlator of the unit 40.

In the invention, the carrier of the transmitter 18 of the probe 10 can be utilized in the transmission of phase information when, for some reason, a transmitter 18 having a carrier frequency generated by a frequency synthesizer is applied, which application is illustrated in Figure 5. If direct synthesis is used in the transmitter 18. the frequency of the reference signal in some integer relationship with the carrier frequency. For example, if the false reference frequency is 10 kHz and the frequency of the carrier 15 is 402.01 MHz, this ratio is 40201. This false reference frequency can be used as the local oscillator frequency of the Omega receiver 20. With the phase lock, another frequency, e.g. 15 kHz, can be made for the local oscillator frequency, which is synchronized to this 10 kHz reference frequency.

20

As shown in Fig. 5, when the above-mentioned pay oscillator information is in the carrier of the transmitter 18, it does not need to be separately modulated, and the receiving portion 20 of the probe 10 is simplified to the shape shown in Fig. 5. The dimensioning of blocks 21, 23 and 24 is performed according to the same principles as described above in connection with Figure 3. The signal R transmitted according to Fig. 5 is reconstructed by the system shown in Fig. 6, according to which at the receiver 50 the carrier of the transmitter 18 is first filtered out or a phase-locked high-frequency signal is formed with respect to it. This can be done, for example, by Rohde & Schwartz's receptionist ET001. When the carrier frequency 30 is available, it is divided by a digital frequency divider 51 by a division ratio of 40201, and thus a reference frequency of 10 kHz is obtained, from which a frequency of 15 kHz is obtained using phase lock circuits 53,54,55 and 56. Thereafter, to generate the 13.6 kHz frequency, mixing between 1.4 kHz and 15 kHz 35 in unit 52 and bandpass filtering in unit 57 are required to obtain the desired frequency component of 13.6 kHz. The general operating principles in this application are otherwise the same as described above in connection with Figures 3 and 4.

12 77341 1 In Loran C applications, the implementation methods are basically the same as when using the Omega system. The frequencies used and the frequencies and bandwidths of the filters and amplifiers must, of course, be selected to suit the Loran C signals.

5

Figures 7 and 8 show an application of the invention for recording a transponder signal. For phase measurement, two simultaneous signals, 75 kHz, CH 2 and CH 2, are required, the phase difference between which is measured. The signal CH1 is a reference signal and the signal passes through the probe 10 and thus the lie of the signal CH1 changes.

According to the principle of the invention, the signal is divided into two components, an intermediate frequency of 15 kHz and a local oscillator frequency, which is divided digitally into a sufficiently low frequency. The pay oscillator-15 frequency of 60 kHz is formed by a phase lock from the reference signal. For recording, both the 9.375 kHz 75 kHz 8'8 and 15 kHz signals are linearly summed according to Fig. 7 into a single channel with a bandwidth of e.g. 20 kHz, i.e. a good quality audlon recorder can be used as the recorder.

20

In Fig. 7, unit 70 denotes a reference preamplifier CH1 limiting amplifier, 71 low-pass filters, 72 level control units, 73 false detectors, 74 low-pass filters, 75 sum amplifiers, 76 band-pass amplifiers, and a 75 kHz signal from the probe is derived, to a bandpass amplifier 78, the signal of which in turn is applied to a sum amplifier 75. The signal received from the sum amplifier 75 is input to a recorder (not shown).

The recorded signal is decoded and reconstructed according to Fig. 8, so that with the bandpass filters or amplifiers 81 and 82, the two signals are divided into different channels. With the false lock circuit 83,84, VC0, the frequency multiplication is performed so as to obtain a reference of 75 kHz. For the second channel, a 60 kHz signal is generated by the phase lock, using which a 15 kHz signal is mixed in 86 units at a frequency of 75 kHz. Finally, only the desired 75 kHz eondislg CH2 is extracted by the cadence pass amplifier 89.

13 77341 Ί In Fig. 8, unit 80 means a buffer amplifier of the signal to be decoded from the recorder with a cut-off frequency f> 20 kHz. Units 81 refer to bandpass amplifiers. Unit 83 is a phase detector and unit 84 is a low pass filter. Correspondingly, unit 85 is a phase detector, unit 5 is a mixer and unit 87 is a low pass filter. A 75 kHz reference signal is output from the system via the CH 2 driver unit 88. The output signal of said mixer 86 is fed to a cathode pass amplifier 89, the output signal of which is a 75 kHz probe signal CH 2.

The following claims set out within the scope of the inventive idea, the various details of the invention may vary and differ from those set forth above by way of example only.

15 20 25 30 35

Claims (9)

A method for transmitting information-containing signals by radio using a narrowband signal channel, the method 5 modulating the carrier with the information-containing signal to be transmitted, the method comprising transmitting the information-containing signal at the transmission end of the method system to the mixing unit (23); applying to said mixing unit (23) a signal from the transmission head local oscillator (22); in said mixing unit (20), a mixing result of said information signal and a pay oscillator signal is generated, the frequency range of which is substantially lower than the frequency range of the information signal to be transmitted; the scrambling result signal obtained in the above-mentioned manner is used as a modulating signal of the radio transmitter (18); and at the receiving end of the transmission system, the detected modulation to be transmitted as a bandpass filter or the like is separated and the signal thus obtained is directed to a receiving end mixer unit (33,52), characterized in transmitting both a signal containing said modulation signal information and sufficiently accurate information from said rado transmitter (18). the frequency and the false signal of the transmitting end mixing signal, i.e. the pay oscillator signal, that the slg-25 signal containing the information about the local oscillator frequency and the false transmission of the transmitting end is also supplied to the receiving mixing mixer (33,52); , which corresponds in information content and frequency to the original information signal of the transmitting end. 1 Claims A method according to claim 1, characterized in that a frequency derived from the reference frequency of the synthesized transmitter (18) is used as the local oscillator signal at the transmitting end, so that information about the frequency and phase of the interfering signal, i.e. the pay oscillator signal, is included in the carrier and transmitted filtering out a carrier frequency divided by a divider unit or units (51,53) whose output signal is transmitted to the output signal of the light detector and whose output signal of the phase detector is applied to the receiving head mixing unit (52) as a local oscillator signal to said mixing unit (52) the detected modulation transmitted to the frequency-10 band, and that the above-mentioned signals are formed into a reconstructed signal in the receiving end mixing unit (52) corresponding to the original information signal of the transmitting end (Figs. 5 and 6). 15 A method according to claim 1, characterized in that the method uses a local oscillator (22), the frequency of which is selected close enough to the frequency of the information signal, and which local oscillator signal is applied to a frequency divider (25) or the like with a local oscillator signal. the frequency is divided sufficiently so that the scrambling result of said mixing unit (23) passed through a suitable bandpass amplifier (24) and the output signal of said frequency divider are applied to a summing unit (26) whose output signal is derived as a modulation signal of the radio transmitter (18); at the receiving end of the system, the bandpass filters 30 (31,32) separate the signal corresponding to the mixing result of the mixing unit and the signal corresponding to the frequency division input of the pay oscillator (22) so that the first signal of the previous stage is passed to the receiving unit mixing unit (33) and the latter the signal is applied to a false air source (34) of the receiving head 35, that the output signal 16 77341 1 of the lock filter formed by said phase detector (34) is applied to said mixing unit (33) as a local oscillator signal, and that the sum of the input frequencies ), from which the system output signal (f) is obtained (Figure 4). Method according to one of Claims 1 to 3, characterized in that the method uses a false-lock column for generating the equivalent of a local oscillator signal of the transmitting end, the phase-lock circuit comprising a phase detector (36; 54) on which a base obtained from a local oscillator signal or filtered 15 signal that the output signal of said phase detector (34; 54) is applied as an input signal of a voltage controlled oscillator (36; 55) or the like; 20 that the output signal of said voltage controlled oscillator (36; 55) or the like is controlled via a frequency divider (37; 56) ¢ 34.54) as a second input signal that the output signal of said voltage-controlled oscillator (36.55) or the like is routed to the mixing head (33.52) of the receiving end as a signal containing information about the local oscillator frequency and phase of the transmitting end. A method according to any one of claims 1 to 5, which is applied in the monitoring of 30 airborne radiosondes, which took place with either Omega or Loran C navigation systems or so-called utilizing a transponder system, wherein the radiosonde (10) comprises a receiver unit (20), a terminal (16) and a radio transmitter portion (18) for transmitting a signal by radio to a ground station comprising a received signal modulation detection unit and a correlator or the like. filtering and mocking unit (40), characterized in that the receiver unit (20) of the probe (10) is subjected to a frequency conversion according to the invention 17 77341 1, which shifts the signal down to a suitable frequency in the baseband and reconstructs the ground signal from the original signals. A method according to claim 5, utilizing an Omega navigation system, characterized in that the receiver (20) of the probe VLF uses an amplifier (21) which is a bandpass amplifier tuned to a suitable frequency and whose preamplifier output signal is applied to a mixing unit. a pay oscillator (22) having a frequency of the order of 12-15 kHz applied to said mixing unit (23), 15 and said mixing unit (23) deriving as a result of scrambling a difference frequency of the order of 1-2 kHz to a bandpass amplifier (24) that said the local oscillator signal is applied to a frequency divider (25) having a division ratio of the order of 5 to 10, and the output signal (S 1 and S 2) of said frequency divider (25) and the bandpass amplifier (24) having frequencies of the same order are fed to the summing unit (26), whose output signal is derived from the modulating signal of the radio transmitter (18) of the probe (10) faults 3 and 4). 25 Application of a method according to one of Claims 1 to 5 for the transmission of a signal, in particular a so-called for recording a 75 kHz or similar signal from a transponder probe with a recorder whose upper cut-off frequency (f ^) is substantially lower than the frequency of the signal coming from the probe, characterized in that the recording method is applied so that the signal (CH 2) to the recorder is frequency converged and that the method uses a reference signal (CH 2) of the same frequency as the signal from the probe, which is formed by dividing the signal stored on the magnetic tape by the recorder 35 and reconstructing the signal probe signal and corresponding reference signal (CH 2). 18 77341 Method according to Claim 7, characterized in that a sufficiently good quality audio recorder is used as the recorder, the upper limit frequency of which is f> 20 kHz, but considerably lower than the frequency of the signal to be recorded (C ^). 5 Method according to one of Claims 1 to 8, characterized in that the method is applied to the transmission of signals whose actual information bandwidth is smaller than the baseband bandwidth of the transmission channel, but the signal frequency itself is greater than this. 15 20 25 30 35 77341 19