JPS6142446B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a noise signal generator that uses a received signal to generate a noise signal that disguises the received signal.

A conventional device of this type is the one shown in FIG. In the figure, 1 is a receiving antenna, 2 is a receiving circuit that captures a predetermined received signal and generates a signal voltage (for example, a discriminator output) corresponding to the frequency of this received signal, and 3 is a white noise generator. 4 is a low-pass filter (hereinafter referred to as LPF) that generates white noise.
5 is an offset voltage generator that generates a predetermined offset voltage, and 7 is a voltage controlled oscillator (hereinafter referred to as VCO) that controls the oscillation frequency depending on the applied voltage. What is controlled, 8 is a high frequency amplifier (hereinafter referred to as
The output signal of the VCO 7 is amplified to a predetermined level using an RFA (referred to as RFA).

FIG. 3 shows signals from various parts of the conventional noise signal generator shown in FIG. 1. Figure 3 a shows the power spectrum of the input signal to the receiving circuit 2, b shows the signal voltage corresponding to the received signal frequency at the output of the receiving circuit 2, and c shows NG.
3, e is the power spectrum of the output of LPF 4, f is the output voltage of LPF 4, g is the output voltage of offset voltage generator 5, h is the output voltage of adder 6, g is the power spectrum of the output of VCQ 7. .

The conventional device has the configuration shown in FIG. 1, in which the input signal frequency is detected by the receiving circuit 2 in order to obtain a noise signal (FIG. 3 i) having a center frequency separated by a predetermined amount from the input signal frequency. A voltage signal corresponding to the frequency as shown in Fig. 3b is obtained, and in advance,
A voltage corresponding to a predetermined frequency polarization with respect to the input signal frequency is set in the offset voltage generator 5 (Fig. 3g), and then the band is determined by LPF 4 of the Gaussian noise obtained by NG3 (Fig. 3c, d). Obtain limited Gaussian noise (Fig. 3 e, f), add these three voltages by adder 6 (Fig. 3 h), and
This is applied to VCTQ7.

Generally, the noise signal obtained by this type of apparatus cannot be precisely matched to a desired frequency, as shown by the dotted line in FIG. 3i.

The reasons for this are: (1) The signal voltage corresponding to the received signal shown in FIG. 3b includes an error due to the frequency discrimination characteristic of the receiving circuit 2.

(2) The control voltage versus oscillation frequency characteristic of VCQ7 is not completely linear.

etc., and these errors are superimposed.

Since the conventional device is configured as described above,
In order to obtain a noise signal in which the center of the frequency spectrum is set accurately to the received signal frequency or a frequency shifted by a predetermined value from this frequency, the frequency vs. output voltage characteristics of the receiving circuit 2, the output voltage characteristics of the offset voltage generator 5, and The control voltage vs. oscillation frequency characteristics of the VCO 7 had to be highly accurate, which posed a problem when building an actual device.

This invention was made in view of the drawbacks of the conventional ones as described above, and uses a so-called Serodyne traveling wave amplifier tube (hereinafter referred to as Serodyne TWT) equipped with a high output amplification function and a phase modulation function. It is an object of the present invention to provide a noise signal generation device that generates a noise signal having a center frequency and frequency spectrum with a predetermined accuracy by performing predetermined modulation and amplification on a signal.

An embodiment of the present invention will be described below with reference to FIG. In the figure, 11 is a receiving antenna, 12
1 is a selection circuit that extracts a predetermined received signal;
3 is a Serodyne TWT that is equipped with an input terminal, an output terminal, and a control terminal, and applies phase modulation to the high-frequency signal applied to the input terminal with a control signal applied to the control terminal, amplifies it, and outputs it to the output terminal;
14 is a sawtooth wave oscillator (hereinafter referred to as SAWGEN), which generates a sawtooth wave signal with a predetermined amplitude and slope; 15 is a white noise generator (hereinafter referred to as SAWGEN);
16 is a low-pass filter (hereinafter referred to as LPF) that applies a predetermined band limit to the white noise; 17 is an adder that combines the output of the SAWGEN 14 with the LPF 16;
The outputs of the SERODINE TWT 13 are added together and the result is led to the control terminal of the Serodyne TWT 13.

As shown in Fig. 2, the noise signal generator of the present application uses the SAW GEN to the modulation input of Serodyne TWT13.
By band-limiting the sawtooth signal from NG 14 and Gaussian noise from NG 15 and adding them together in adder 17, a Gaussian signal whose center is a frequency shifted by a predetermined amount from the input signal frequency is generated. This is to obtain a noise signal with a power spectrum. The deviation of the center frequency of the noise signal from the input signal frequency is proportional to the slope of the SAM GEF 14 sawtooth signal.

First, the principle of frequency conversion of Serodyne TWT 13 will be explained. The structure of Serodyne TWT13 is schematically shown in FIG. As is clear from Figure 4, Serodyne TWT13 has an RF input terminal, an RF output terminal,
It consists of a modulation signal input terminal, and the modulation signal supplies a helical voltage.

FIG. 5 shows an outline of frequency conversion by speed modulation of the Serodyne TWT 13. When a sawtooth wave is applied to the modulation signal input terminal, the propagation time between the input and output also changes in a sawtooth manner, and as a result, the signal period, that is, the frequency, appearing at the output terminal changes. Figure 5a,
b indicates a case where the frequency shifts high and a case where the frequency shifts low, respectively.

The present invention is a noise signal generator that utilizes the frequency conversion function of the Serodyne TWT13.

The operation of the noise signal generator using the Serodyne TWT 13 will be explained in FIG. As shown in FIGS. 6a and 6b, when the modulated input signal of the Serodyne TWT 13 is constant, the propagation time is also constant and no frequency conversion occurs. As shown in FIGS. 6c, d, e, and f, when the modulated input signal is made into a sawtooth wave, a signal that is shifted upward or downward from the input signal frequency is obtained at the output depending on the sign of the slope.

Next, as shown in FIG. 6h and g, the Gaussian noise of the NG 15 is band-limited by the LPF 16, added by the adder 17, and applied to the modulation input to obtain a noise signal with a Gaussian power spectrum. These signals are shown in FIG. 6 i, j, k, l.

The present device, which generates a noise signal based on the above principle, has the following advantages compared to conventional devices.

Conventional equipment flatly discriminates the input signal frequency.
While the VCO is controlled, this device directly performs frequency conversion on the input signal, so
No discrimination circuit is required, and no errors occur due to discrimination characteristics.

With SAW GEN 14, a sawtooth voltage with excellent linearity can be easily obtained.

The Serodyne TWT13 has a high-output amplification function, so there is no need for a high-frequency amplifier in the output stage as in conventional devices.

Note that if a semiconductor phase shifter is used instead of the TWT, even better broadband characteristics can be obtained.

In the above embodiment, the passband of the LPF 16 is made to have no steepness or cut-off characteristics, but the passband characteristic may be made into a Gaussian function. In that case, the output of the Serodyne TWT 21 has a power spectrum that is close to a rectangle. This is particularly effective when a sloppy signal appears and it is desired to suppress the spread of the power spectrum.

As described above, according to the present invention, since the noisy FM signal generator is configured by the Serodyne TWT, there is no need for a device to accurately measure the frequency of the input signal, and the frequency is precisely equal to the input signal frequency. Alternatively, a noisy FM signal whose power spectrum is centered at a point exactly deviated from the input frequency by a predetermined frequency can be easily obtained. Furthermore, the bandwidth of the power spectrum can be arbitrarily obtained over a wide range from narrow to wide. Furthermore, since the Serodyne TWT itself also serves as a high-output amplifier, a high-output amplifier is not required in the output stage.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing a conventional device, Fig. 2 is a diagram showing an embodiment of the present invention, Fig. 3 is a waveform explanatory diagram showing the operation of the conventional device, Fig. 4 is a configuration diagram of Serodyne TWT, and Fig. 5 6 is an explanatory diagram of the frequency conversion operation of the Serodyne TWT, and FIG. 6 is an explanatory diagram of waveforms of each part of FIG. 2. DESCRIPTION OF SYMBOLS 1... Receiving antenna, 12... Selection circuit, 13... Serodyne TWT, 14... Sawtooth wave oscillator, 15...
White noise generator, 16...Low pass filter, 17... Adder.

Claims (1)

[Claims] 1. Has an input terminal for applying an input signal, an output terminal for outputting an amplified signal, and a helical electrode for controlling beam speed and transmission phase, and controls the signal voltage applied to the helical electrode for transmission. A traveling wave tube having a serrodyne amplification effect whose phase can be changed, a noise signal subjected to a predetermined band limitation, and a sawtooth signal having a predetermined slope and amplitude are superimposed to form the traveling wave tube. A means for applying voltage to a helical electrode is provided, and the signal voltage applied to the helical electrode of the traveling wave tube is controlled to modulate the signal passing through the traveling wave tube to generate a high frequency noise signal having a predetermined center frequency and bandwidth. Noise signal generator.