JPS6228108Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a carrier frequency measuring device that measures the carrier frequency of a signal whose carrier wave is suppressed, such as an SSB wave.

In SSB, DSB, A ₈ waves, etc., the carrier wave is suppressed and transmitted, and in these various communication methods, the frequency difference between the center frequency of the carrier wave and the sideband wave is within the permissible range specified by law. There must be. Radio wave monitoring services or transmitter manufacturers that use these communication methods need to measure whether the radio waves meet the standards.

Conventionally, a receiver compatible with each communication method is used to extract the carrier wave and measure the frequency of the carrier wave, but simply using a receiver does not separate the sound from the voice and audio signal components are mixed in. The drawback is that the signal-to-noise ratio is poor and the carrier frequency cannot be measured accurately.

Figure 1 shows a commonly used SSB receiver. In the figure, 1 is a high frequency amplifier, 2 is a first frequency converter, 3 is a first local oscillator, 4 is a first intermediate frequency amplifier, 5 is a second frequency converter, 6 is a second local oscillator, and 7 is a second intermediate frequency amplifier. 8 represents a frequency amplifier and a demodulator, respectively.

On the output side of the first intermediate frequency amplifier 4, an audio signal component S _i and a carrier wave component S _C are obtained as shown in FIG. The frequency characteristics of the first intermediate frequency amplifier 4 are as shown as a curve 9 in FIG.

In order to extract the carrier wave component _SC in such a receiver, the reception frequency is shifted so that the intermediate frequency _C of the carrier wave component _SC matches the center frequency of the first intermediate frequency amplifier 4, as shown in FIG. In this state, only the carrier wave component _SC is extracted from the output side of the first intermediate frequency amplifier 4 as shown by the dotted line.

However, even if the reception frequency is shifted so that the carrier wave component S _C becomes the center of the reception frequency, the audio signal component S _i will be mixed in because the frequency bandwidth of the first intermediate frequency amplifier 4 is wide, and the frequency measurement of the carrier wave will be difficult. It has the disadvantage of causing interference. Therefore, it is difficult to measure the carrier frequency unless the carrier component S _C can be extracted with a good signal-to-noise ratio near the transmitter. However, there is also the drawback that audio cannot be monitored in this state.

The purpose of this invention is to provide a carrier frequency measuring device that can measure the frequency of a carrier wave without being interfered with by audio components, and can also monitor audio during the measurement.

FIG. 4 shows an embodiment of this invention. In this invention, a narrow band filter 11 is provided on the output side of the first frequency converter 2. As shown in FIG. 5, this narrow band filter 11 has a frequency C that is shifted from the center frequency ₀ of the first intermediate frequency amplifier 4 by a frequency _B , which is the difference between the frequency _C of the carrier wave component _{SC .}
Assume that the center frequency is . The Radio Law stipulates that the distance between the carrier wave and the center frequency of the sideband wave is 1.5KHz. Therefore, if the center frequency of the first intermediate frequency amplifier 4 is 455 Hz, the center frequency of the narrow band filter 11 is selected to be 435.5 KHz. Although the example in FIG. 5 shows the case of the upper side band method, it is assumed that the same relationship is selected in the case of the lower side band method. The narrow band filter 11 only needs to have a bandwidth sufficient to extract the carrier wave component _SC , for example, 435.5K.
It is sufficient to select a bandwidth of approximately Hz±200Hz. In reality, a maximum of ±300Hz is allowed.

By providing the narrow band filter 11 in this manner, the carrier wave component S _C can be extracted from the narrow band filter 11 while the audio is being monitored.
At this time, the bandwidth of the narrowband filter 11 is set to ±300Hz.
If the selection is made as follows, no audio component will be mixed into the passband of the narrowband filter 11. Therefore, from the narrow band filter 11, a stable carrier wave component S _C
By supplying the carrier wave component S _C to the frequency measuring device 12, the frequency of the carrier wave can be accurately measured.

Therefore, according to this invention, the carrier wave component S _C can be extracted from the S/N ratio since the carrier wave component S _C can be extracted while monitoring the voice without being interfered with by the voice. Therefore, the frequency of carrier waves such as SSB can be stably measured even at a location quite far from the transmitter.

If a frequency measuring device with an averaging function is used as the frequency measuring device 12, the extracted carrier wave component S
Accurate measurements can be made even if the signal-to-noise ratio of _C is poor. This averaging function, for example, measures frequencies within the passband of the narrowband filter 11 at regular frequency intervals, integrates the measured values at each frequency measurement point, and divides the integrated result by the number of integrations. In other words, it averages out. Therefore, the integrated value is concentrated only at the frequency measurement position where the carrier wave component exists, and at other frequency positions, the integrated value approaches zero due to the noise component, and therefore the SN of the extracted carrier wave component is
Even if the ratio is poor, the carrier frequency can be measured with high accuracy.

[Brief explanation of the drawing]

Figure 1 is a system diagram to explain the configuration of a conventional SSB receiver, Figure 2 is a graph to explain its operation, Figure 3 is a graph to explain the conventional carrier wave extraction method, and Figure 4 is a graph to explain the conventional carrier wave extraction method. The figure is a system diagram showing one embodiment of this invention, and FIG. 5 is a graph for explaining the operation of the main parts of this invention. 1: High frequency amplifier, 2: First frequency converter,
3: first local oscillator, 4: first intermediate frequency amplifier,
5: second frequency converter, 6: second local oscillator,
7: second intermediate frequency amplifier, 8: demodulator, 11: narrowband filter, 12: frequency measuring device.

Claims (1)

[Scope of utility model registration request] In a receiver that receives a signal with a suppressed carrier wave, the output side of the frequency converter has a center frequency that is separate from the intermediate frequency amplifier and is shifted by the frequency difference between the center frequency of the intermediate frequency amplifier and the carrier frequency. A carrier frequency measuring device that is provided with a narrow band filter and extracts a carrier wave component from the narrow band filter.