JPS5819069B2 - spectrum analyzer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a spectrum analyzer, and particularly to a spectrum analyzer that prevents noise other than a target signal from appearing on a display screen in logarithmic display mode.

In a spectrum analyzer', signal observation is generally performed in two ways.

That is, there are two methods: a near display mode in which the change in input level is proportional to the output level, and a logarithmic display mode in which a wide dynamic range is achieved by logarithmically compressing the input level.

In this logarithmic display mode, as shown in FIG. 1, not only the spectrum 1 of the target signal but also noise 2 such as internal noise are displayed.

For example, if the signal level is 0 [dB], (m(7)
When a signal is observed using a system with an S/N ratio of 50 (: dB,), the direct ratio of the signal to noise level is (300:1), but when observed after logarithmically compressing this, it becomes as shown in the figure. 50 (dB) below the signal level
Noise is simultaneously displayed at the bottom, and the level ratio on the display screen deteriorates to (5:1).

Therefore, there is a drawback that the resolution is degraded and it is not possible to observe small-level target signals.

In the logarithmic display mode in which the input level is logarithmically compressed and observed, it is necessary to remove noise.

In view of this point, the present invention is designed to remove noise with a simple configuration.

Hereinafter, one embodiment of the present invention will be described with reference to FIG. 2. In the figure, 3 is an input terminal to which a target signal is supplied, and 4 is a mixer.

The mixer 4 is supplied with a local oscillation output from a local oscillator 5.

A control signal synchronized with a horizontal sweep signal of an oscilloscope (not shown) is supplied to the local oscillator 5 from a terminal 6.

The output of the mixer 4 is supplied to a band pass filter 7, where only a predetermined frequency component is extracted and further supplied to an adder circuit 9 via an amplifier 8.

A signal obtained by adjusting the output of an oscillator 11 to a predetermined level by a level adjuster 12 is injected into the adder circuit 9 via a switch 10 .

The output of this adder circuit 9 is supplied to a logarithmic compression amplifier 13□, and the output thereof is further supplied to a detection circuit 14.

The output signal obtained at the output terminal 15 of this detection circuit 14 is applied to the Y-axis (vertical axis) input terminal of the oscilloscope.

In the above configuration, assume that two target signals with levels O(d,B) and -45(dB) are generated on the input side of the amplifier 8, and the S/N of the amplifier 8 is is 50 (dB), and its output contains noise of -50 (dB, 1 to 60 (dB, 1) in addition to the above-mentioned target signal.

Now, when the switch 10 is turned off, both the target signals 1a and Ib and the noise 2 are displayed on the display screen of the spectrum analyzer, as shown in FIG. 3A.

As is clear from FIG. 3A, no noise is displayed in the spectrum display portions of the target signals 1a and 1b.

This is because the noise is masked by the level difference between the target signal and the noise.

Then, by turning on the switch 10, a signal having the same frequency (not necessarily the same frequency) as the target signal appearing at the output of the amplifier 8 and whose level is slightly higher than -50 (dB) is sent to the adder circuit 9. Supplied.

At this time, the noise 2 is removed and no longer appears on the display screen of the oscilloscope, as shown in FIG. 3B.

In this case, the level of the injected signal must be lower than the level of the target signal 1b -45 (dB).

Otherwise, this target signal 1b would also be suppressed.

As described above, according to the present invention, noise can be removed from the display surface, target signals of relatively low level can be observed, and the resolution of the spectrum analyzer can be improved.

Furthermore, if the level of the signal to be injected is varied by the level adjuster 12 according to the noise level, it is possible to suppress noise of any level.

Furthermore, the configuration of the present invention differs from the conventional spectrum analyzer in that it includes an oscillator 11, a level adjuster 12, and a switch 1.
It is sufficient to simply add 0 and the adder circuit 9, which has the advantage of not affecting other circuits in any way.

Note that the present invention can also be applied to XY display devices other than oscilloscopes.

[Brief explanation of drawings]

FIG. 1 is a route map used to explain the spectrum analyzer, FIG. 2 is a system diagram of essential parts of an embodiment of the present invention, and FIG. 3 is a route map used to explain the same. 1.1a and Ib are target signals, 2 is noise, 9 is an adder circuit, 11 is an oscillator, 12 is a level adjuster, and 13 is a logarithmic compression amplifier.

Claims (1)

[Claims] 1. A mixer to which an input signal through an input terminal and an output signal of a variable frequency oscillator are mixed, a band-pass filter to which an output signal of this mixer is supplied, and an output signal of this band-pass filter. An adder circuit to which an injection signal of a predetermined frequency is added; a logarithmic compression amplifier to which the output of the adder circuit is amplified; a detection circuit to which the output of the logarithmic compression amplifier is supplied; Display device Y
Spectrum analyzer configured to be supplied to the shaft input terminal. □ ゛・ □