JPS58148528A - Squelch circuit - Google Patents

Abstract

PURPOSE:To discriminate noise from program sound in response to the state in change of a value of a autocorrelation function and to ensure the squelch operation, by applying a reception output signal to an autocorrelation function generating means and supplying a autocorrelation function output signal to a squelch discrimination means. CONSTITUTION:An IF signal from an input terminal is demodulated at a frequendy discriminator, and the demodulating signal is applied to a level comparator 9 of an autocorrelation function computing section via an equalizing LPF. The level is compared with a reference level at the comparator 9, the result of comparison is stored in a shift register 10, and the output of the register 10 is applied to counters 16-19 via AND gates 12-15 wich a clock of a timing clock generating section 11. The counters 16-19 count the number of outputs of each register stage, each coefficient of a polarity autocorrelation function is outputted and applied digital comparators 20-24. The output is compared with each reference level at the comparators 20-24, the discrimination output of the squelch is generated from an AND gate 12 in response to the result of comparison, and the squelch operation is made suitable and sure.

Description

Detailed Description of the Invention The present invention rapidly demodulates an intermediate frequency stage signal in a 1M relay broadcaster, creates an autocorrelation function of this demodulated signal, and uses this function pattern to modulate the intermediate frequency signal. This is a squelch circuit that discriminates whether the received signal is an unmodulated signal, an unmodulated signal, or amplified noise due to the absence of the received signal. This is suitable for controlling the broadcaster output of the local station to stop so as not to radiate noise radio waves when the radio frequency runs out.

Conventionally, when the master station's radio waves stop, K performs an operation of stopping its own radio waves, that is, a squelp operation.

The intermediate frequency (IF) stage signal q FM is demodulated, the -f: demodulated signal vtso kHz is passed through a bandpass filter to extract the /10 kHz component, and when the /10 kHz component is detected at a certain level or higher, , it assumed that the master station's radio waves had stopped and performed a squelp operation.

With this method, as shown in Figure 1, even composite signals during stereo broadcasting! Frequency components below J kHz are controlled i! 8 degrees Celsius, so if the master station's radio waves are being received, the temperature is about 3 times higher! In principle, the OkHz component is not clogged, but if the radio waves from the master station are not received, the gain of the relay broadcaster increases due to automatic gain control (AGC), and the noise in the receiving section is amplified.

Therefore, the fact that tsOkHs IR component is also generated is used to detect this tsOkHz 771 minutes. However, this method, commonly known as noise squelch, has problems such as the occurrence of a /10 kHz component due to the characteristics of the limiter and 1M detector when there is too much interference, and the mutual fWa of 1!
There was a drawback that erroneous judgments were made due to the generation of OkHz components, and the broadcasting was stopped. Therefore, in order to prevent this noise squelch from malfunctioning, the intermediate frequency band carrier wave v10.7 MHz is extracted using a band-pass filter, and when the carrier wave is detected, 11, /! It may be possible to supplement the noise squelch by setting the signal so that it does not stop even if the signal is detected, but if the receiving frequency and the transmitting frequency are close to each other, the radio waves from the master station may be sent out when the signal stops. There is a drawback that the noise component received by the receiver may be mistakenly determined to be a signal from the master station, and the noise may continue to be emitted.

SUMMARY OF THE INVENTION An object of the present invention is to provide a squelch circuit tfM that can eliminate the above-mentioned drawbacks and properly and reliably realize a squelch operation.

In order to achieve such an object, one aspect of the present invention is to guide a received output signal to an autocorrelation function generating means to generate an autocorrelation function output signal, and supply the autocorrelation function output signal to a squelch discriminating means to generate an autocorrelation function output signal. The present invention is characterized in that pre-program and noise are discriminated according to the state of adjustment of the autocorrelation function value with respect to the change in the correlation variable value.

The present invention will be described in detail below with reference to the drawings.

FIG. 2 shows an example of the configuration of the squelch circuit of the present invention. Here, l is an input terminal of the frequency discriminator, and this input terminal supplies the IP signal of the KFM relay broadcasting machine. The frequency discriminator section demodulates the baseband up to 000Hz. This frequency discrimination i! The demodulated output signal from - is equalized by a low-pass filter P J [11] Bandwidth limitation is performed in order to suppress the quality of sample points to be compared, which will be described later. Next, by adding the output of the equalization low-pass filter J to the autocorrelation function output signal and calculating the autocorrelation function of the demodulated signal, an output that is modulated by the frequency component of the IP flaw signal to the input terminal l is obtained.

For example, the autocorrelation function for the signal shown in Figure 3 (A), in which Gaussian noise with uniform frequency components is band-limited to 0 kHz, is calculated in the calculation section as shown in Figure 3 (CB), and the same Gaussian noise Bandwidth m1ll to 100 kHz
i! The autocorrelation function for the signal shown in Figure 1 (A) is obtained as shown in Figure 3 (B).

In general, when Gaussian noise with power spectral density ωゎ is band-limited at frequency f@Hx, the autocorrelation number ψ(
is expressed as . This equation is a function that decays as τ increases, but if fa is multiplied by a factor of 1, as the variable is represented by fc·τ, the attenuation will be multiplied by a factor of .tau..

Therefore, in Fig. 3(B), the first zero point is Bμ-@C1, and in Fig. 3(B), the first zero point is D2! It becomes μs@a. Also, when τ=O, (0) becomes the power of the input signal.

Always maximum. Therefore, ψ(0) at τ;O and τ=j
na, 10 ns, /j ns,
−〇am etc. ψ(s), tp side.

ψ), etc., and the magnitude of each ψ(τ) is ψ(0)
No.

If it is below a set value such as K, it can be determined to be uniform Gaussian noise up to 100 kHz, and if it is above the set value, it can be determined to be a signal with a narrow band. In addition, the noise at the end of the broadcast is stationary, but before the program there is a non-modulated state due to speech "seki" etc., so ψ(0) becomes small and there is stuttering, so there is 9(O). If it is less than the set value, it is determined that there is no modulation, and a squelch operation is performed in parallel with the determinations such as ψ(5) to 9I-) described above. Before the actual program, /j k
The components are not uniform up to Hz, and statistically it is 10k.
It is sufficient to set it below Hz. Therefore, /(J kHz
The following components and No. 1, which is AM-modulated with a signal of 10 kHz or less centering on n k)fz and the carrier wave is suppressed, are the pre-program signals, and the broadcast ends vk&'! Since the triangular noise peculiar to FM signals is obtained as a signal that extends to a sufficiently high frequency range, the judgment section! Now, based on the above principle, the squelch operation for the output of the correlation function calculation section can be performed without interference.

A determination output is obtained from the output terminal 4.

Here, a detailed example of the autocorrelation function calculating section 5 and the determining section 5 is shown in FIG. In this example, autocorrelation function calculation 54I-
The polarity autocorrelation in which the number pattern grows quickly is taken, and the circuit can be simply configured with registers and counters. First, the autocorrelation function ψ(rino-film shape) is given by the first-order equation (1).

If we express this in a discrete form using the clock period Δτ.

becomes. Regarding the polarity correlation function ψp(mΔτ)K used in this example, in this equation (2), the correlation is determined by dividing the amplitude of f(nΔτ] into λ values with respect to the threshold value X, which becomes - By using A (t), give the polar correlation in the form.

In FIG. 5, autocorrelation function calculation output terminal 711Ck
1. The baseband signal from the equalization low-pass filter J is supplied, and the reference input terminal trc sets the threshold value of the level comparator D. The level comparator D generates an output °l" or "O" in accordance with the magnitude of the signal at the input terminal 7, that is, in accordance with the threshold value Xo shown in equation (3). /7) It is taken into the L/ register 10 in synchronization with the clock cycle CL/ from clock generation tie/.

Assuming that the input signal to the foot register is 8(t), the input signal 8(t+n·Δτ) delayed by an integer multiple nΔτ of the clock cycle Δτ of the clock cycle CL/ is stored as the register output. The first output of the register 10 and the output CL of the timing clock generator/l are added together to obtain an AND output, and the counter 16 counts the number of times the AND output becomes 11".Counter 14 corresponds to m-0, and the final counting result is the coefficient ψ(0) of the autocorrelation number. The AND output obtained by supplying the AND output is supplied to the counter 17, and the counter 17 counts the number of times that the AND output becomes "/" K:.The counting result of the counter 7 is the coefficient ψ[k1 of the autocorrelation coefficient. ], which corresponds to 1m=kl.Similarly,
The output of AND gate/2 and kl of register 10,
・・・・・・The k1th output is antgeton-1・
-, /JK are supplied respectively, and each AND output is supplied to the counter /JK.
I, .
l) is the counter ll,...

Obtained from /de.

Here, each output of the counters 16 to 9 counted up to T with NΔτ as the autocorrelation function calculation period T is supplied to the digital comparators X to 2# forming the judgment section j, and the setting levels supplied to these comparators are Compare with each value of ~J/ at the input terminal.

Each comparison output of these comparators J-3 is supplied to an AND gate B, and, for example, the autocorrelation function calculation output is shown in FIG.
) or CB), and outputs the determination output to the terminal 6. For example, in FIG. 7(B), τ is 2! If it is more than μS, the presence or absence of autocorrelation corresponds to the autocorrelation function value, so select the m value to be 2j μm or more in τ, and use the output of AND gate B to calculate Be able to determine which of the following is the case.

Note that the output of the digital comparator
/ is the theoretical value of ψ(0).

This value determines the difference between 1 when normal program sound is not modulated (・
) can compensate for misjudgments caused by fluctuations in

In FIG. 5, the tying clock generator l/
From there, the recent pulse Rsl of /6~/ji and the recent pulse F of ~21 are sent to the digital comparator.
Lsco (period T) is generated.

As described above (1) According to the present invention, squelch operation can be realized while avoiding malfunctions due to interference waves and overmodulation.
When polar autocorrelation is used as in the example shown in the figure, the autocorrelation function calculation section can be configured simply using a foot register and a counter, and therefore the device can be made into LaI.
As a result, reliability is improved, the surface area occupied on one circuit board is reduced, and the device can be made more compact.

[Brief explanation of drawings]

Figure 1 is a frequency spectrum diagram of normal stereo broadcasting, Figure 1 is a block diagram showing a configuration example of the present invention, Figure 1 (A)
, (B) and the reference figure (mu), (B) are from this engine 1
FIG. 8 is a block diagram showing a specific example of the present invention; FIG. l...input terminal, c...frequency discrimination section,
3... Equalization low-pass filter. Hiroshi: Autocorrelation calculation section, j: Judgment section, ≦... Judgment output terminal. 7... Self-phase M function calculation unit input terminal, r... Reference input terminal, 9... Level comparator, 10... Foot register. //- Tying clock generator, ! 2~/S,) J・-and gate, /6~/9...Counter. X~2f...Digital comparator, b~J/...
- Setting level input terminal. Patent applicant: Japan Broadcasting Corporation (A> (A) Figure 3 (E) (Bn → ′ζ (ps)

Claims (1)

[Claims] 1) Guide the received output signal to an autocorrelation function generating means to generate an autocorrelation function output signal Y, and supply the autocorrelation function output signal t to a Skelna discriminating means to detect a change in the autocorrelation variable value. A squelp circuit having a device configured to discriminate between one-program sound and noise according to a state of change in an autocorrelation value. 2) The autocorrelation number M generation means includes a level comparator that compares the received output signal with a reference level, a shift register that stores the comparison result Y, and a shift register that stores the comparison result Y; Each coefficient of the polar autocorrelation function by counting the number? and a plurality of digital conhalers for digitally comparing outputs from the plurality of counters with a plurality of reference levels; The comparison output from the halter is supplied, and the squelch judgment output is generated according to these comparison outputs.