DE1282741B - Narrow band transmitter in which a single sideband signal is generated by modulating a first carrier signal with a communication signal - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. Cl .:

H03c

German class: 21 " a4- 14/01

Number: 1282 741

File number: P 12 82 741.7-35 (G 45596)

Filing date: December 30, 1965

Opening day: November 14, 1968

The invention relates to a narrow band transmitter in which a single sideband signal by modulating a first carrier signal is generated with a message signal.

The modulation systems currently used for communication based on frequency modulation, Phase modulation, amplitude modulation, single sideband modulation, double sideband modulation, Residual sideband modulation or the like, each have certain advantages and disadvantages.

A significant advantage of frequency modulation (FM) systems used in communications widely used is their high transmitter output power. C output amplifiers that have high output power output at high efficiency can be used in FM transmitters as they are the frequency or phase modulation of the carrier signal do not distort. As the message of an FM signal in the zero crossings of the carrier signal is included, so any amplitude modulation has no meaning and usually through Limitation in the transmitter and receiver is lifted, has an amplitude distortion as a result C operation of an output amplifier has no effect, so that the FM transmitter has a high transmission power. In addition, the FM systems are in frequency modulation because of the noise reduction or noise attenuation relatively noise-free. These are major advantages that have helped the Frequency modulation is widely used in communications engineering. However, it has long been known that the FM systems normally use the frequency spectrum very poorly and a large one Require bandwidth. This leads to great difficulties when the available frequency spectrum is limited. So are z. B. in the case of land vehicles, the channels available for the transmission of messages extremely narrow. However, the implementation of narrow band FM systems requires special complicated ones and complex circuits, e.g. B. for pre-emphasis, limitation, post-equalization, etc. Furthermore, are The FM systems are exposed to "threshold" effects that change the signal-to-noise ratio of a Receiver quickly deteriorates and the signal can not be used when the noise level exceeds a critical level, commonly called a threshold. So while an FM system Advantages in terms of output power and relative freedom from noise above the threshold value has, its disadvantages are the poor utilization of the frequency spectrum and the sensitivity to it Threshold effects.

Narrow band transmitter where a
Single sideband signal by modulating a
first carrier signal is generated with a message signal

Applicant:

General Electric Company,

Schenectady, N. Y. (V. St. A.)

Representative:

Dipl.-Phys. F. Finally, patent attorney,

8034 Unterpfaffenhofen, Blumenstr. 5

Named as inventor:
Alex Charles Latker,
Johannes Jacobus Jandegraaf,
Lynchburg, Va. (V. St. A.)

Claimed priority:

V. St. v. America January 4, 1965 (423 093)

In contrast, single sideband modulation systems advantageously have a relatively narrow bandwidth. However, some of the modulating messages are transmitted in the form of amplitude modulation of the single-sideband signal, so that single-sideband transmitters must have a very linear output characteristic (Α output amplifier) and operation as a C output amplifier with its high efficiency is excluded. Therefore, a single sideband transmitter has a small output power. Furthermore, if the lowest frequency to be transmitted of the communication signal is reduced, it becomes increasingly difficult to suppress the carrier signal and the neighboring components of the unused sideband signal. If z. B. an audio frequency message signal of f _m = 0.3 to 3 kHz is used, the distance between the unused and the used sideband signal is only 600 Hz and only 300 Hz for any carrier signal deviation, even with the carrier signal suppressed. The manufacture of narrow-band filters with a well-defined cut-off frequency to suppress the carrier signal and the unused sideband signal becomes quite difficult, especially at high frequencies. If z. B. the carrier signal frequency f _c = 40 MHz, the upper sideband _{signal (/ c} + f _m ) is between 40.0003 MHz and 40.003 MHz, while the lower sideband signal

809 637/1088

3 4

band signal (f _c - f _m ) between 39.9997 MHz and carrier signal sent, so that the total effect is 39.997 MHz. The manufacture of a filter that is maintained at the same level as the narrow band transmitter allows the upper sideband signal to pass through, but if desired the narrowband transmitter can be constructed so that the 40 MHz carrier signal and the lower sideband signal that the second carrier signal suppresses one of the signals is currently an insoluble one 5 your first carrier signal has a different frequency, problem. There are no known physically feasible frequency mixers between the out filters that provide such a filtering amplifier and the phase comparator. It is therefore currently impossible to unilaterally generate the frequency of the band signal directly in the VHF range for the phase comparison. Transmit signal in the frequency of the single sideband If convert the single sideband signal at these frequencies io signals.

is required is a complicated sequence of several The narrow band transmitter can thereby be improved ren modulation steps necessary to the end, that the frequency converter to obtain an integrating frequency. It is understandable that in the .RC network for setting a specific frequency the presence of several frequency conversions has frequency pass band of the frequency converter or has frequency modulations for generating a one-sided 15. The frequency pass band can e.g. B. band signal of the desired frequency of effort (/ ₀ 4- 0.3 kHz) to (/ ₀ + 3 kHz). In this way, as well as the costs of such a system, intermodulation and distortion can increase proportionally. frequencies are suppressed, and the narrowband

It is therefore the object of the invention to specify a narrow characteristic of the narrow-band transmitter can be better band transmitter, which the high output 20 are guaranteed. Such a frequency output of an FM transmitter with the good utilization of the narrow band transmitter can, however, also use a circuit other than a; integrating rc unites. Network can be reached » _:

The invention is particularly based on the knowledge. The invention should be closer to the drawing

based on the fact that the amplitude modulation of an input 25 will be explained. It shows

sideband signal suppressed and its remaining- F i g. 1 is a block diagram of the narrow band transmitter

permanent frequency modulation by controlling a according to the invention and

Frequency converter for generating a frequency Fig. 2 to 4 a number of curves, - the test modulated Transmission signal can be used. show results for the narrowband transmitter

A narrow band transmitter of the type mentioned at the beginning 30 of FIG. 1 was obtained.

is characterized according to the invention in that the narrow-band transmitter of Fig. 1 is divided into two limiter the single-sideband signal, so main functional blocks, namely that the message is contained in the zero crossings of a single-sideband signal generator 1 and a limited single-sideband signal that the Frequency converter 2 with a frequency converter limited single sideband signal a frequency converter 35 borrowed oscillator 14. An example, audio frequency after to generate one of the frequency modulation of the directional signal modulated with the frequency in the limited single sideband following transmission signal seitenbandsignalgeneratorl a first carrier signal f _c , constant amplitude controls that the frequency so that a single sideband signal; and then a converter that generates a second carrier signal is severely limited, as a result of which the amplitude mode frequency variable oscillator, a downstream oscillator is essentially canceled and the C output amplifier and one between the message only in the frequency modulation, i.e. in the output amplifier and the oscillator has the zero crossings of the limited single sideband phase comparator, which is contained by phase comparison signals. The average power of the limited one-sided distance signal with the transmission of the transmitted message signal is thus signal delivers a control signal to the oscillator. " ⁴⁵ significantly increased, so that the efficiency of each

Since, on the one hand, the frequency range of the transmission following signal transmission is increased while

signals because of its frequency modulation of the quality of the transmitted message signal,

limited single sideband signal following Fre- d. H. of the tom or speech signal, practically not

frequency modulation is essentially the same as that of the affected. The limited single sideband signal

Is the single sideband signal, the good utilization ⁵ ° is generated by the single sideband signal generator 1 for fre-

of the frequency spectrum is passed to the oscillator 14 as in the single sideband quenzümsetzer 2. Of the

modulation achieved, so a transmission signal with very oscillator 14 generates a second carrier signal, its

narrow bandwidth, while on the other hand frequency ^ _{0 is} generated by the single sideband signal.

a high efficiency wi & in an FM transmitter controls that the oscillator 14 of the frequency

due to the use of the C output amplifier 55 modulation of the single sideband signal. exactly follows so

is achieved without the above-mentioned threshold that the output signal · of the frequency converter 2

value effects occur .. or the transmitted signal is an extremely narrow signal of

In an advantageous further development of the invention, the amplitude can be constant. That the input signal

the narrow-band transmitter be designed in such a way that that of the frequency converter 2 is severely limited, i. H. any-

Also limiter the first carrier signal from the 60 amplitude modulation; from the single sideband carrier signal generator receives to the limiter. signal has been removed, the "limited input

to full limitation during the intervals to, sideband signal in frequency converter 2 by a

start in which no single sideband signal emp- C output amplifier 15 with high efficiency

will catch. This has the advantage that the narrow-gauge are amplified, so that · the output power of the band transmitter the second carrier signal is further increased during this 65 narrow band transmitter, because any-

Sends intervals and thereby the noise under which amplitude distortions, as a result of the C-loading

presses during the intervals in which the follow-up remains unauthorized; and by limitation

direction signal is transmitted, but the second can be removed because the entire message

5 6

In the frequency modulation of the transmission signal, the direct limitation of the speech signal is countered. Since no carrier signal or lower page sentence has been generated to limit the speech signal after the band signal, no frequency conversion in the mixer 6 to the degree of narrow band filter is required in order to reduce the unused page of the compression that can be achieved, as the quality of the band signal or the carrier signal increases suppress. 5 speech signal due to harmonic distortion

The single sideband signal generator 1, which generates the single sideband signal, which is largely unlimited in terms of the fundamental frequencies in the speech signal, shows that it is understandable. The in F i g. i illustrated one-source of the audio-frequency message signal a sideband signal generator 1 avoids this Schwie microphone 3 or the like. The Naehrichteflsignal is rigkeit in that the speech signal peaks are first passed through a band filter 4 in order to cut the message after the speech signal is converted into a signal on a suitable frequency band, e.g. B. from other part of the frequency spectrum by the 0.3 to 3 kHz, to limit. The message signal mixer 6 has been implemented.
is amplified in an amplifier 5 and together Since the message or speech signal is converted beforehand into a higher frequency spectrum with the first carrier signal f _c from a quartz (i.e. controlled carrier signal oscillator 7 to a mixer 15 in the single sideband signal), the limiting stage 6 influences headed, the z. B. a push-pull modulator that can even be 30 to 70% or more. The message signal generates an upper and a lower sideband speech signal in the can, practically not the intelligibility of the mixer 6. Harmonic distortion of the / + (0.3 to 3 kHz) and f _c - (0.3 to 3 kHz). If a normal mixer stage is used for the language of the limited single sideband signal, there is no longer a problem, since the harmony also the first carrier signal f _c at the output, since it can easily be filtered out by means of suitable circuitry, in contrast to a push-pull modulator as a mixer. Furthermore, the frequency stage suppresses an ordinary mixer stage, the carrier signal converter 2 practically all harmonic distortion not suppressed. The upper sideband signal is what will be explained. There is some intermodulation distortion through a filter 8 to a limiter 9, but this left after it has passed in an amplifier 10 does not have much influence because, firstly, subjective has been strengthened. The first carrier signal f _c from the hearing test, which will be described later, ge carrier signal oscillator 7 will have shown via a line 11 that the intermodulation distortion and a potentiometer 12 also to the limiter 9 generally does not disturb the listener and the confused. The amplitude ratio of the pre-limited 3a verbosity is not affected. Further upper sideband signal and the first carrier suppressed the frequency converter 2 also a signal f _c is adjusted so that in the absence of the essential part of that Intermodulationsver message signal and thus the upper sideband distortion caused by the strong limitation of the one signal, the level of the first Carrier signal f _{c out-of-side} band signal arises in limiter 9. This is sufficient to cause the limiter 9 to be fully limited to such a processing of the message signal so that any noise can be suppressed, an effective increase in the amount transmitted. However, if the message signal and thus power are reached between 8 and 13 db of the upper sideband signal, this can be without at the same time disadvantages in the form of amplitude of the upper sideband signal so excessive of distortion and a reduction in intelligibility that the limiter 9 enter the full limitation of patency.

leads and both the first carrier signal and the strong limitation of the single sideband signal im Noise suppressed. In this way, the single sideband signal generator 1 also transmits in an improved manner Narrow band transmitter of Fig. 1 the full (second) the accuracy, the stability and the efficiency Carrier signal during the intervals in which the narrowband transmitter is in operation. The Frehaupt Kern message signal is present, so that 45 frequency converter 2 controls its oscillator 14 so that the second carrier signal quieter the receiver or the frequency modulation of the single sideband mute power and the noise in the receiver signal follows by continuously changing the frequency of the suppressed. During the intervals in which the single sideband signal is at the frequency of the broadcast message signal is present, on the other hand, only signals in a phase comparator 20 are compared to the single sideband signal transmitted, so that throat is 5 °. Phase comparators are, although they are theore-reducing of the efficiency through the superset only to phase changes of two alternating carrying of the unmodulated carrier signal occurs. addressing input signals, actually also opposing

Due to the strong limitation of the single sideband and amplitude changes of one of the signals empsignals the actually transferred average is sensitive. If the SSB signal is so limited power is increased significantly, so that the output 55 is that it is with constant amplitude to the phase power of the narrow band transmitter is enlarged. comparator arrives, the errors that result As is known, the message signal power can be amplitude modulation of one of the input signals change strongly, e.g. B. the voice signal power can occur within, greatly reduced, so that the ability of one large volume range. So generated at the speed of the oscillator 14, the frequency modulation of the Voice transmission to follow a speaking person very precisely in the 60 single sideband signal, further average a speech signal that improves a volume.

range of about 30 db with a peak The single sideband signal with constant amplitude

Average value ratio of about 10 to 13 db from the limiter 9 (f _c + 0.3 kHz - ^ / _c + 3 kHz),

includes. If the volume range of the speech, as already mentioned, go to frequency converter 2

signals could be compressed somehow, 65 routed, which could do the voltage-controlled frequency the mean power of the speech signal effectively variable oscillator 14, the second

increase. The direct limitation of the speech carrier signal with the frequency f _{0 is} generated. The Fre-

signals is one way of doing this. However, the reduced frequency of the oscillator 14 follows the frequency modulus

7th 8th

! ation of the single sideband signal in order to dimension an output mixer 17 and the phase comparator 20) so signal with appropriate frequency modulation that the frequency converter 2 generates the. The output signal from the oscillator 14 will have the desired frequency passband, which will be explained in more detail in one or more C output amplifiers 15. The 5 network 21 which is coupled to an antenna 16 is preferably a proportionality network, since the and radiate into free space. By means of the oscillator 14 in the frequency converter 2, one or more C output amplifiers 15 operating correctly with respect to transient signals at saturation, an amplitude modulation of the has, which cause the oscillator 14 to generate an over-oscillator output signal through the limiting we- or under-correction of the Make frequency, kung of the output amplifier 15 eliminated and thus io if he suddenly has to follow voltage changes, a transmission signal with constant amplitude generated, as z. B. in the output signal of the mixer 17, whereby the frequency of the transmission signal can occur synchronously if rapid frequency changes occur in conjunction with the frequency modulation of the limited input in the control signal from the limiter 9. Therefore, in the sideband signal from the single sideband signal generator, the network 21 is preferably changed to an i? C integer. The transmission network emitted by the antenna 16, which cancels the influence of this transient signal, is therefore a signal with constant amplitude, signals. The network can also have a frequency in our case between the DC amplifier to generate the desired / ₀ + 0.3 kHz and / ₀ + 3 kHz, so that the signal th frequency pass band of the frequency conversion of a single sideband signal with constant amplitude be zers 2. For example, network 21 may be something like this. It can be seen, however, that the sub-ao selected is that the frequency passband is 0.3 to 3 kHz compared to single sideband modulation transmitters.

at the same time there is no carrier signal and no lower Through the network 21 thus the frequency

Sideband signal can be generated. That makes fixed converter 2 as a band filter for the output signal of the

Filter for the suppression of undesired fre-limiter 9. The output signal of the limiter 9

frequency deviations of the carrier signal and the un- 25 namely has undesired harmonics of

The sideband signal used is superfluous and has f _c - (f _c + 3 kHz) and intermodulation frequencies

avoids all difficulties normally associated with as a result of the simultaneous limitation of different

the manufacture of filters with the required frequency components.

sharp filter characteristics at high frequencies As mentioned above, allows the correct connected. · 30 dimensioning of the network 21 the frequency. The frequency modulation of the oscillator 14 is modulation of the variable frequency oscillator 14 controlled by the frequency converter 2 so that the within the frequency pass band.
Oscillator 14 follows the frequency of the single sideband signal in the narrowband transmitter shown in FIG. 1 as precisely as possible and preferably unambiguously. is the fundamental frequency of the output signal of the For this purpose, the output signal from the oscillator 14, the frequency / _{0 of} the second carrier output amplifier 15 is sampled and converted into a further signal. In some cases, especially if a push-pull modulator or a mixer 17 with a very high frequency / _{0 is} desired, it may feed, however, where it is advisable to mix the frequency of the oscillator 14 'with a frequency f _{T with a reference signal} or is superimposed on it. Which is lower than / ₀ and by one or more frequency / _r is equal to the difference between 40 frequency _{multiplier steps is multiplied to / 0} , the frequency / _{0 of} the second carrier signal and It can be seen that in this case the frequency f _r of frequency f _c of the first carrier signal taken of the output signal of the frequency synthesizer (fr ⁼ U ~ fc)> ^to th ^e frequency of the transmission signal 19 as f _r = f fc must be ₀ ~ before.
into that of the limited single sideband signal. It can also be seen that it can clog in some cases. The reference signal f _r is not necessary in a 45 that the limited single sideband circuit with a crystal-controlled oscillator 18 signal in the frequency spectrum through the oscillator 14 and a normal frequency generator 19 (with Fre- is converted by the frequency f _{0 of} the second quenzsynthese) generated, which can have one or more Stu carrier signals of the frequency f _{c of} the first carrier for frequency multiplication. signal is different. In this case, the frequency modulation of the output signal of the 5 ° circuit for generating the reference signal f _r , the mixer 17 should exactly correspond to the frequency modulation of the crystal-controlled oscillator 18, the standard frequency limited single sideband signal from the single sideband frequency generator 19 and the mixer 17, signal generator 1 . The output signal can be omitted, and the transmission signal can be sent directly to the mixer 17, the other input signal is sampled in the phase comparator 20 and compared to the phase comparator 20, in which it can be viewed with 55. It can be seen that other scarf band signals are also compared. The output signal of the line in the narrow band transmitter according to the Erfin phase comparator is proportional to its size, in which the fretional to the frequency difference between the input frequency modulation of the limited single sideband signals, while its sign indicates the direction of the signal that is to be transmitted Represents message. Frequency or phase deviation of f _c . The output signal of the phase comparator 20 is compared in order to generate the control signal for the oscillator generating the transmission via a network 21 as a control signal to the oscillator signal, so that 14 is given so that the frequency modulation of the frequency modulation of the Transmission signal of the Fredes limited single sideband signal follows from single sideband frequency modulation of the single sideband signal,
band signal generator I follows. 65 The variable frequency oscillator 14 may be of any known type. The network 21 will, in connection with that, be of any known type. For example, other circuits of the frequency converter 2 (ie LC feedback circuits of the oscillator 14, the output amplifier 15, the Colpitts, Hartley etc. can be used.

The oscillator expediently has a chip sensitivity to amplitude noise and.

variable capacity on, e.g. B. one in the output power of the C output amplifier without

Reverse biased p-n-period (sometimes the associated disadvantages of an excessively

Called varactor) as part of the oscillator frequency range and from threshold value effects

determining resonance circuit. By changing the 5 will be. Furthermore, a better spectrum distribution

bias voltage applied to the diode in reverse mode than achieved even with narrowband FM. It

direction, the transition capacity is changed, there are no threshold limits as with Fre-

the resonance frequency of the resonance circuit and thus frequency modulation, so that the transmitter gain

the oscillator frequency changes. Optionally, it can be increased or, in other words, an equal

also voltage-controlled high-frequency oscillators, id valuable communication links with much weaker ones

like klystrons and resistance tube modulators signals can be sustained as it is with

be used. FM transmitters is possible.

It can thus be seen that the narrow band transmitter F i g. 2 to 4 represent curves obtained in an adequate the invention, a transmission signal with a constant number of tests were obtained with a Generated amplitude, the frequency modulation of which the ig narrowband transmitter according to the invention durchge-frequency modulation of the limited single sideband, the tests showed that the signal from the single sideband signal generator 1 follows narrow band transmitters according to the invention a minimum the bandwidth used by the transmission signal is at least as good, but usually better in terms of spec equal to the bandwidth of the message transport utilization as frequency modulation with very signal is. Although this broadcast signal is equivalent to ao narrower bandwidth, which almost reaches the good, Frequency utilization of the single sideband modulation can be considered for an upper single sideband signal can as it has the same frequency range and which comes on while simultaneously using the same with FM Bandwidth like the single sideband signal, transmitters achieve the transmission power that can be achieved. These and in a normal single sideband receiver, tests further showed that an additional transmitter can receive and can be demodulated, it will be without a gain of 9 db compared to a narrow band simultaneous Generation of neither a carrier signal frequency modulation in terms of intelligibility nor a lower single sideband signal is generated, it occurs and the transmitter does not meet the threshold value effect it can also be seen that by replacing the filter 8, the FM transmitter is defeated.

are shown in Einseitenbandsignalgenerator 1 through a filter for the tests, the results in Fig, 2 and 3 for the lower sideband and by the choice of 30, a narrow-band transmitter was prepared according to f _r = / ₀ + ic for the frequency synthesizer 19 of the invention with a Frequency f _c = * 43 MHz allows a lower single sideband signal to be sent. The transmitter was able to do this through VOSIM. Thus the narrowband modulation (speech simulation) is modulated and the transmitter according to the invention is basically measured from the transmission signal with an analyzer with an on »basic circuit for the generation of one-sided resolving power of 3 kHz. (The VQSDVl · band signals in that only one signal with the frequency modulation is eüj more common in communications engineering that the message to be transmitted is generated according to the standard test that is held in the "EIA standard RS 152 A". A carrier signal is only described.) These measurement results are generated in FIG. 2 when no message is transmitted, so plotted as curve 25. At the same time, in this case the output signal of the limiting 40 visual band (+ 5 kHz deviation) FM transmitter was modulated in the single sideband signal generator 1, the first by VOSIM modulation and the Fre carrier signal with the frequency /,., The output Measured frequency spectrum of the transmission signal and plotted as the signal of the phase comparator 20 zero and the curve 26 off. It can be seen that the output signal of the oscillator 14 is the second carrier transmission signal with a constant amplitude of the narrow signal with the frequency f ₀ . The second carrier band transmitter according to the invention, a narrower signal is therefore only sent in the absence of a message bandwidth than the narrowband FM transmitter, signal to make the noise very small while at the same time with an FM transmitter or to reduce. reproducible transmission efficiency is available.

It can also be seen that the frequency converter 2, as shown by curve 25, the transmission signal is un-

has a very narrow bandwidth, making it almost as narrow as a very narrow FM signal and

monic or intermodulation distortion which im even a bit narrower, although it is a bit more

Single sideband signal generator 1 or in the C output bandwidth as a single sideband signal (8 kHz to '

amplifier 15 is generated, suppressed or down to 20 db) takes,

can be significantly reduced. In a similar test, the Scbmalbancl · ·

Difference between the narrow band transmitter of 55 transmitter according to the invention and a narrow band!

Fig. 1 and the normal circuit for the generation FM transmitter by inputting two tones of

generation of a single sideband signal in which both 1 kHz and 3 kHz are tested and the transmitted signal with

an upper and a lower sideband signal are measured by an analyzer. The results are in

and one of them by a narrow curve 27 and 28 for the narrow band transmitter

band filter is suppressed. It is therefore evident 60 according to the invention or for a narrow band

that the narrow band transmitter according to the invention represented the FM transmitter. Again it can be seen

Advantages of both the frequency modulation and that the narrow band transmitter according to the invention

The single sideband modulation achieved by the good or equivalent to a narrowband FM transmitter

Utilization of the spectrum by single sideband is even better than this. For both curves is

transmitter is achieved without a linear operation 65 the entire bandwidth approximately 18 kHz, the

with an associated low transmission power level varies by up to 25 db. It can also be seen

is necessary, while the advantages of the frequency modulation, that the bandwidth, which accounts for 99% of the transmitter power

lation in the form of a simple circuit, which includes un-two-tone modulation, is only 11 kHz,

- ■■■ ■ _. .1 ...-. J. ■ - ■ - (.'.- .- 'i- -----: 809637/1088

as can be seen in the figure between points 29 and 30. This shows that the narrow-band transmitter according to the invention has all the advantages of both good bandwidth utilization and high transmission efficiency. . ' The. Understandability of a weak signal from the narrowband transmitter according to FIG. The invention was compared with that of a narrowband FM transmitter to determine the advantages of the narrowband transmitter according to the invention. which has threshold value effects, Fig. 4 shows the result of the tests, which were several speech comprehension tests for different input signal levels, where the Harvard word lists were used. The receivers were adjusted to the same noise level, six different word lists from the Havard speech intelligibility series were used and about 50 tests were carried out. The percentage of word intelligibility is plotted on the ordinate and the signal intensity in - dbm on the abscissa. The curve 31 relates to the signal from the narrow-band transmitter according to the invention and the curve 32 to an FM receiver. It can be seen that for signal levels below -116 dbm the drop in the curve 32 is so steep that it can be understood As even, for a very Jyour increment of signal loss is reduced very quickly. This shows, that the transmitter is at or below the FM threshold. is working. With 30% word intelligibility (which corresponds to a sentence intelligibility of 50%), the gain compared to the FM transmitter is 9 db. With a word intelligibility of 50%. (which corresponds to a sentence intelligibility of 80%) the improvement is 6.5 db compared to a narrowband FM transmitter. With a word intelligibility of 85% (which corresponds to a sentence intelligibility of 97%), the improvement over the narrowband FM transmitter is even better than 3 db. That shows that the. severe limitation of the SSB signal from SSB signal generator 1 does not significantly affect the intelligibility of the signal and that the. the same intelligibility can be achieved with less effort. The narrow-band transmitter according to the invention thus allows further power savings compared to a narrow-band FM transmitter, in that a signal 3 to 9 dB weaker ensures the same intelligibility of words and sentences as with a narrow-band FM transmitter According to the invention, a message transmission by weak signals which are below the FM threshold value and are usually not usable in an FM transmitter In addition, a good utilization of the frequency spectrum is achieved which, under certain conditions, results in a significant reduction in the distance required between adjacent communication channels, since the bandwidth of the transmission signal is extremely narrow. ., '<··'^;

Claims (2)

Claims:; ... 1. Narrow band transmitter with> a one-sided fc band signal by modulating a first .. Carrier signal generated with ein'Nacnrichtensignäl is characterized by . that a limiter (9) that _; Single sideband signal limited so that the message in the zero crossings of the limited single sideband signal escaped. • hold is that the limited single sideband signal a frequency converter (2) for generating a ■ the .frequency modulation _?; -des ⁷ ; limited. A ¹ - sideband following transmission signal more constant _r amplitude controls that. "the frequency conversion ; .zer (2) a second carrier signal (/ ") erzeil · · low frequency variable oscillator (14), _f a downstream C output amplifier (15.) , and one between the output amplifier ^! . (15) and the oscillator. {14j '; switched phase • has comparator (20), · the] rdureh · phase equilibrium of the limited single sideband signal; init "dem .Send signal a control signal to the oscillator r (14) Hefert. - · - - - H ':; .- ^? -. ^-:; \; '■ - -ά ., 2. Narrow band _{transmitter ::} > ^ oh claim .: 1, da-. characterized by - that the limiter (9) ..- also the first carrier signal _; (^,) from the carrier ^ · ] receives signal generator (7) in order to cause the limited to full limitation during "the, intervals ztf in which no single sideband signal is received. -" Υ. "...;« -?, ^: r · '- .. 3. Narrow band transmitter according to claim 1, characterized in that ⁱ dassi, the second 'carrier signal (Z ₀ ) one of the ^ first ^: carrier signal (/ _c ) different frequency.; ha1i.; - and that a. Fri ₇ __ ,. mixer (17) between the output ... stronger (15) and the phase comparator (2Q ^ .. is switched in order for the phase comparison the * _-> Frequency of the transmission signal oil-the frequency of the To implement single sideband signal. ' ^! · "_; 4. Narrow band transmitter according to claim 1, da- ,; marked by; that the frequency converter (2) is an integrating .RC network (21) * to set a certain frequency by? . _: has the range of the frequency converter. Considered publications:
-Vilbig, "Textbook of High Frequency Technology", 2nd edition, 1939, Leipzig, pp. 622 to 689. 1 sheet of drawings 809 637/1088 11.68 © Bundesdruckerei Berlin