JPS6051067B2 - Signal strength measurement method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for detecting a weak signal from noise and measuring the signal strength.

For example, if we consider the case of an omega signal, if it is received at a point very far from the transmitting station, the S/N will be less than CdB with a normal receiver (bandwidth of several Hz to several tens of H2) and will be proportional to the signal strength. It is difficult to reproduce an envelope waveform with such a large size. An object of the present invention is to be able to measure the signal strength of a signal with good phase stability, such as an omega signal, even in a region with poor S/N ratio. The figure shows an embodiment of the present invention, in which 1 is a signal input terminal, 2 is a tracking filter, 3 is a phase shifter, 4 is a reference wave oscillator, 5 is an attenuator, 6 is an adder, 7 is a tracking filter, and 8 is a phase comparison It is a vessel.

A tracking filter 2 removes noise components contained in the phase information of the input signal from the signal under measurement applied to the signal input terminal 1 . In a situation where the S/N is poor, the bandwidth of this tracking filter can be reduced to several tens of minutes -H.
It becomes necessary to narrow the range to -H2 of 2 to several hundredths or less. The tracking filter 2 that satisfies this requirement is usually constructed from a digital tracking filter, but in such a construction, only phase information appears in its output, and amplitude information disappears. The phase information output from the tracking filter 2 is sent to the phase shifter 3, where the phase is advanced by θ. That is, a signal whose phase is advanced by θ with respect to the signal component Asinω applied to the signal input terminal 1 is generated. The reference wave oscillator 4 is a sine wave oscillator with a constant amplitude, and oscillates in synchronization with the output of the phase shifter 3. Therefore, its output becomes sin (ω is +θ). This output passes through the attenuator 5, and the reference wave that becomes Bsln (ω is +θ) is then sent to the input terminal J terminal 1 by the adder 6.
The signal under measurement applied to the signal under test and the output of the reference wave oscillator 4 are added, and the noise component of the input is removed by the tracking filter. Note that this tracking filter 7 is similar to the tracking filter 2. Therefore, the phase information of the sum of the signal component 7 and the reference wave oscillator output appears in its output. A phase comparator 8 compares the outputs of the tracking filters 2 and 6, and controls the attenuator 5 based on the result to change the amplitude of the reference wave input to the adder 6. Since it is configured like this,
The amplitude (intensity) of the signal can be determined by the magnitude of the control amount of the attenuator 5. In other words, the signal component is Asi
If nωt, the output of the reference wave oscillator is Bsin(ωt+
θ), so if we add these two, we get AsinO)t
+Bsin(ωt+However, Tanα=BsinO/(A
+BcOsθ). The influence of noise included in the phase of the signal can be removed by the tracking filter, so there is no need to consider it. Now, what is the phase difference found by the phase comparator 8?
As is clear from this equation, it is α. That is, if α is determined, since θ is known, the amplitude A of the input signal component can be determined. Although the explanation has been given here by advancing the phase by θ with the phase shifter 3, it goes without saying that the same effect can be achieved even if the phase is delayed by θ. here,
The amplitude of the input signal component can be determined by controlling the attenuator 5 so that the phase difference between the outputs of the phase comparator 8 is a constant value θo.

That is, the formula Tan=Bsinθ/(A+BcOsO)
Since B is controlled so that α=θo (constant value), the value of A can be determined by reading the amplitude B of the reference wave, that is, the amount of attenuation of the attenuator 5.
Note that it is usually most stable when θ is 900 and 00 is 45. As explained above, if this method is used, only the phase information needs to be handled to measure the signal strength, and A
- It can be realized using an entirely digital circuit without using a D-cochverter, etc., and the signal strength can be measured regardless of the amount of noise.

Therefore, when measuring the electric field strength of a signal with a poor S/N ratio such as an omega signal, or when the electric field strength is known, there is an advantage that the gain of the receiving system (especially the antenna) can be easily measured.

[Brief explanation of the drawing]

The figure is a block diagram showing one embodiment of the present invention. 1... Signal input terminal, 2, 7... Tracking filter, 3... Phase shifter, 4...
...Reference wave oscillator, 5...Attenuator, 6.
... Adder, 8 ... Phase comparator.

Claims (1)

[Claims] 1. A means for removing noise components from an input signal to extract a signal component, a means for generating a waveform whose phase is advanced (or delayed) by θ than the phase of the signal component, and a means for generating a waveform whose phase is advanced (or delayed) by θ from the phase of the input signal. or delayed) waveforms, and means to remove noise components from the added signal, measure the phase difference between the input signal and the added signal, and use this result to calculate θ for the signal component. A means for controlling the amplitude of a waveform whose phase is advanced (or delayed) by 0.05 is provided, and the amplitude is controlled so that the phase difference between the input signal and the added signal is constant. A signal strength measurement method characterized by determining the amplitude of an input signal from the amount of amplitude.