JPH0433424A - Transponder - Google Patents

Abstract

PURPOSE:To reduce a noise level by disposing a frequency compressor circuit compressing the frequency of a transponder operating signal to the pre-stage of a band pass filter. CONSTITUTION:A signal S5 is detected by an envelope detecting circuit 7 to obtain a signal S6 representing the amplitude characteristic and the signal is shaped by a waveform shaping circuit 8 to obtain a transmission driving signal S7. Then the transmission driving signal S7 drives a transmission signal generating circuit 9 to send a transponder response signal S8 in the sea water. Thus, when a reception signal passes through a band pass filter 6, the reception signal is compressed 100 times by a pre-stage frequency compression circuit 3. Thus, the noise level is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to transponders, and particularly to long-distance or high-noise resistant transponders.

[Conventional technology]

Conventionally, this type of transponder includes a transducer 1 that receives a transponder activation signal S1, a preamplifier circuit 2 that amplifies the received signal, and a received signal S2, as shown in FIG.
Enter the center frequency f.

and the output signal 35' of the bandpass filter 6'.
an envelope detection circuit 7 that detects the envelope of , a waveform shaping circuit 8 that generates a transmission drive signal S7 from the envelope detection output signal 36', and a transponder response signal S8 from the transducer 1.
The transmission signal generation circuit 9 is configured to transmit a signal.

The transponder activation signal S2 amplified by the preamplifier circuit 2 has the frequency characteristics shown in FIG. 4(a), and has a bandwidth Bw,
By passing through the bandpass filter 6' having a center frequency f0, the frequency characteristic becomes as shown in FIG. 4(b). When the envelope of the bandpass filter output signal S5' is detected, a signal S6' having the amplitude characteristic shown in FIG. 4(c) is obtained, and this waveform is shaped to drive the transmission signal generation circuit 9 as shown in FIG. 4(d). transmission drive signal S7
and transmits a transponder response signal S8 into the sea.

[Problem to be solved by the invention]

By the way, in such a transponder, in order to detect the envelope of frequency 10 as shown in FIG. 4(c), the signal-to-noise ratio (S/N) of the bandpass filter output signal S5' must be
ratio) must be greater than the circuit-specific S/N setting value,
In order to increase the response distance of the transponder, the signal f0
It is necessary to reduce the noise level commensurate with the level reduction. The noise level is expressed by equation (1), and in order to reduce the noise level, it is necessary to narrow the bandwidth B8 of the bandpass filter 6'.

NL = NSL + 10101o - (1) NL: Noise level (dB) NSL: Noise spectrum level at frequency 10 (
d B re 1 μbar ) Bo : Bandpass filter passband width (H2) Therefore, in conventional transponders, in order to reduce the noise level, a bandpass filter 6' with a very narrow band is used. There must be.

However, the narrower the bandwidth, the larger the bandpass filter itself becomes. There is a problem in that it becomes difficult to realize a transponder for distance use and high noise resistance.

SUMMARY OF THE INVENTION An object of the present invention is to provide a compact and high-noise resistant transponder that can reduce the noise level without using a bandpass filter with a narrow bandwidth.

[Means to solve the problem]

The transponder of the present invention includes a frequency compression circuit that compresses the frequency of the transponder activation signal before a bandpass filter that performs bandpass filtering of the transponder activation signal.

Further, it is preferable to include an oscillator and a mixer that convert the frequency of the frequency-compressed signal so that the center frequency of the frequency-converted signal matches the center frequency of the transponder activation signal.

[Effect]

According to the present invention, by compressing the frequency of the signal,
A bandpass filter with a bandwidth of B8 can be made into a bandpass filter with an apparent bandwidth of B, 1/frequency compression ratio, and the input noise level can be reduced without increasing the size of the bandpass filter.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram of one embodiment of the present invention.

In the figure, 1 is a transducer that receives the transponder activation signal S1, 2 is a preamplifier circuit that amplifies the received signal, 3 is a frequency compression circuit that compresses the frequency by a required multiple, here 100 times, and 4 is a frequency compression circuit that compresses the frequency by a required multiple, in this case 100 times. The oscillation circuit 5 is a mixing circuit that mixes the respective outputs of the frequency compression circuit 3 and the oscillation circuit 4. Also, 6 is the center frequency 10Ofof+ (H
z), a bandpass filter with a bandwidth B1, 7 an envelope detection circuit that detects the envelope of the output signal of the bandpass filter 6, and 9 a waveform that generates a transmission drive signal from the output signal of the envelope detection circuit. The shaping circuit 9 is a transmission signal generation circuit that transmits a transponder response signal from the transducer 1.

The operation of the transponder having this configuration will be explained with reference to the waveform diagrams shown in FIGS. 2(a) to 2(f).

Transponder activation signal S1 of frequency f0 is transmitted to transducer 1
The received signal S2 is received by the preamplifier circuit 3 and is amplified by the preamplifier circuit 3 to produce the received signal S2 shown in FIG. 2(a). This received signal S2 is compressed by a factor of 100 in the frequency compression circuit 3, resulting in the frequency characteristic shown in FIG. 3(b). The received signal S3 after 100 times compression is sent to the oscillation circuit 4.
The signal with a frequency of 11 generated in the above is mixed in the mixing circuit 5, and sum and difference frequency components are generated to form a signal S4 having the frequency characteristic shown in FIG. 2(C). This signal S4 is passed through a bandpass filter 6 to a center frequency ioo r shown in FIG. 2(d).

f+(Hz), resulting in a bandpass filter output signal S5 with a bandwidth B8.

In addition, by appropriately setting the frequency f of the mixing circuit 5, in this example, the frequency of the mixed difference frequency 10°f, -f can be made to match the center frequency f0 of the transponder activation signal S1 before compression. This allows the use of the same bandpass filter 6 as the conventional bandpass filter 6'.

This signal S5 is detected by the envelope detection circuit 7 and is shown in FIG.
) is obtained, and by shaping it in the waveform shaping circuit 8, the transmission drive signal S7 of FIG. 2(f) is obtained.
is obtained. Then, the transmission signal generation circuit 9 is driven with this transmission drive signal S7, and the transponder response signal S8 is transmitted into the sea.

Therefore, in this operation, when the received signal is passed through the bandpass filter 6, the received signal has been compressed by a factor of 100 by the frequency compression circuit 3 in the previous stage.
Even if filtering is performed using the same bandwidth B as in Figure (b), the appearance is that the uncompressed received signal S2 is filtered using the bandwidth B, / 10
This is the same as filtering with 0. As a result, the noise level obtained from the above equation (1) is -20d
B (101 og (1/100)). Therefore, if the signal-to-noise ratio for signal detection is the same as that of a conventional transponder, the transponder according to the invention has a 20 dB improvement in noise immunity, or it is possible to move the transponder away to a distance where the transponder activation signal is reduced by 20 dB from the current point. It will be possible.

〔Effect of the invention〕

As explained above, the present invention has a frequency compression circuit that compresses the frequency of the transponder activation signal before the bandpass filter that performs bandpass filtering of the transponder activation signal. The appearance of the corrugated equipment is upper B. It becomes a bandpass filter with a bandwidth of 7 frequency compression ratios, and has the effect of reducing the input noise level without increasing the size of the bandpass filter.

In this case, the amount of reduction in the input noise level can be determined by changing the frequency compression coefficient.

Furthermore, by converting the frequency of the signal so that its center frequency matches the center frequency of the transponder activation signal, the same bandpass filter as before can be used.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the transponder of the present invention, FIGS. 2(a) to f) are waveform diagrams of signals in each part of FIG. 1, and FIG. 3 is a block diagram of an example of a conventional transponder. , FIGS. 4(a) to 4(d) are waveform diagrams of signals at each part of FIG. 3. DESCRIPTION OF SYMBOLS 1... Transducer/receiver, 2... Preamplifier circuit, 3... Frequency compression circuit, 4... Oscillation circuit, 5... Mixing circuit,
6.6'...Band filter, 7...Envelope detection circuit,
8 Waveform shaping circuit, 9... Transmission signal generation circuit. Figure 4

Claims (1)

[Claims] 1. A transponder that performs bandpass filtering of a transponder activation signal, performs envelope detection and waveform shaping to generate a transmission drive signal, and transmits a transponder response signal based on this transmission drive signal. 2. The transponder according to claim 1, wherein a frequency compression circuit for compressing the frequency of the transponder activation signal is disposed upstream of the bandpass filter. 2. The transponder according to claim 1, comprising an oscillator and a mixer for converting the frequency of the frequency-compressed signal, and the center frequency of the frequency-converted signal is made to match the center frequency of the transponder activation signal.