JPS606137B2 - AFC method using modulated waves - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention modulates a transmission signal with an identification signal and sends it out, and on the receiving side, uses the identification signal to perform AFC operation in a local VCO, and prevents malfunctions caused by external radio waves. This invention relates to an AFC method that is also used as a discrimination signal.

A conventional device of this kind has a configuration diagram as shown in FIG. 1, where 1 is a transmitting signal generator, 2 is a transmitting antenna, 3 is a receiving antenna, and 4
5 is a high frequency amplifier including a mixer, 5 is an intermediate frequency amplifier that also serves as a limiter, 6 is a frequency discriminator that detects the AFC signal, 7 is an amplifier that amplifies the AFC signal, and 8 is a local oscillator.

The transmission signal is emitted from the antenna 2, and this signal is transmitted to the antenna 3.
The signal is received by the high frequency amplifier 4, mixed with the signal from the local oscillator 8, and guided to the frequency discriminator 6 via the intermediate frequency amplifier 5.
When the frequency of the intermediate frequency coincides with the center value, an atmospheric potential appears in the output signal, and when it deviates from the center value by either 10 or -, a 10 signal or a - signal appears. This signal is amplified by an amplifier 7 and added to a local oscillator 8 to perform an AFC operation. In this case, there is a drawback that when an interfering signal of the same frequency is received, the AFC operates on that signal, and in order to compensate for this drawback, it is necessary to make the output level of the transmitted signal on the transmitting side higher than that of the interfering wave signal. In order to eliminate such drawbacks, the present invention applies shallow frequency modulation to the RF signal on the transmitting side using the identification signal fw and sends it out, and on the receiving side, the local VCO uses the frequency modulated signal using fw. A
This is to perform FC operation.

In addition, it is characterized by the provision of a discrimination circuit that turns on the AFC loop system only when there is both an intermediate frequency detection output and an FM demodulation output of W, which will be described in detail later. The purpose is to apply tracking ArC only to the transmitted signal without being affected.

FIG. 2 is a block diagram of an embodiment of the AFC circuit according to the present invention, and 11 is an RF signal generator that is swept by, for example, a motor.

12 is an oscillator for the identification signal fw, 13 is a modulated wave generator,
The identification signal oscillator 1 receives the RF signal from the RF signal generator 11.
It applies shallow FM modulation using the identification signal from 2 and radiates its output from the antenna 14.

This radiated signal is received by the receiving antenna 15, and this received signal and the output voltage from the local VC024 are combined into a mixer (
The output from the mixer 6 mixed by the mixer 16 is converted to an intermediate frequency and amplified by an intermediate frequency amplifier 17 which also serves as a limiter.

The output of the intermediate frequency amplifier 17 is sent to an intermediate frequency tuned detector 18.
, are added to the frequency discriminator 19 and the intermediate frequency detector 22.

As is clear from the frequency vs. demodulated output voltage characteristic diagram in FIG. 3, the output of the intermediate frequency tuning detector 18 is 2W of the signal frequency-modulated by the identification signal fence at the tuning frequency mo, and the signal is demodulated by IF-△. In the region of F, E1 and sinW are demodulated. For example, cosfw is demodulated in the IF+ΔF region. That is, the phase of fw is reversed around the tuning frequency IFo. In this way, the intermediate frequency tuned detector 18
An output signal with a phase change depending on the input frequency of IFo-ΔF, mo or IFo+ΔF is applied to the phase detector 20.

On the other hand, in the frequency discriminator 19, the output signal frequency f
Due to the nature of w', it is hardly subject to phase changes, so when this world power signal frequency fw is applied to the phase detector 20, this 20 performs the following operation. The phase detector with the configuration shown in Fig. 4 is well known, but the output of the intermediate frequency tuning detector 18 is applied to the terminal R, and the output of the frequency discriminator 19 is applied to the terminal L. It means that it was done.

Terminal 1 corresponds to 20 output terminals. Here, a signal of the same frequency fw is applied to both R and L terminals, but
From the terminal 1, a DC output as shown in the phase difference versus phase detection characteristic diagram of FIG. 5 is obtained corresponding to the phase difference between the output signals 18 and 19.

That is, the intermediate frequency tuned detector 18 and the frequency discriminator 1
When both output signals of 9 are in phase, the negative maximum D is output from terminal 1.
A C output signal is obtained.

If there is a phase difference of 90 degrees between the two output signals, the output of the terminal 1 will be O, and if there is a phase difference of 1800 degrees between the two output signals, the maximum positive DC output signal will be obtained from the terminal 1. Here, the positive and negative DC output signals are sent to the phase detector 2
Of course, if the sacrifice of the connection of the diode at 0 is made different from that shown in the figure, the polarity of the positive and negative DC output signals can be inverted and a DC output signal can be obtained. It has a frequency band range as shown in the figure, and in the range of IFo ΔF, for example, from 6 day z to 7 day z, a detection output of, for example, 15 V can be obtained as an output signal.

Now, shallow FM modulation is applied to R using the identification signal frequency.
Considering the case where only the F signal is being received, both the outputs of the intermediate frequency tuned detector 18 and the frequency discriminator 19 are phase detected by the phase detector 2, and from this 20, the phase difference between the two outputs is detected. A DC output signal in a form corresponding to this can be obtained. In this state, the intermediate frequency detector 22 and the frequency discriminator 19 have obtained the above-mentioned DC signal of, for example, 15 V and the output signal of fw, respectively, so these two signals are applied to the discrimination circuit 23. Therefore, in order to operate the switch of the switch circuit 21 in a closed state, the DC output signal of the phase detector 20 is supplied to the local oscillator VC024, so that the AFC operation is performed to pull this 24 to the intermediate frequency IFo. That is why it is done. This is the case where the fw signal is present on the input side of the discrimination circuit 23 and the output of the intermediate frequency detector 22 is present. No fw signal, 2
If there is no output of 2, it can be considered that the RF signal is not being received from the receiving antenna 15.

In this case, 21 is naturally in an open state. Now, next, in addition to the received RF signal of the main button, the RF signal of the outer button is simultaneously transmitted to the antenna 1.
If received from 5, it will be as follows.

The intermediate frequency amplifier 17 has a limiter function so that the outputs of the intermediate frequency tuned detector 18 and the frequency discriminator 19 are not affected by amplitude fluctuations.

If the level of the external RF signal is much higher than the original RF signal level, the external RF signal is compressed by the limiter function 17. At this time, the original RF signal is also compressed, making it impossible for the intermediate frequency tuning detector 18 and frequency discriminator 19 to function adequately (the egg signal becomes smaller or becomes zero).
.

Therefore, the function of the phase detector 20 becomes incomplete or stops. In this case, even if the limiter function 17 is operating, the intermediate frequency detector 22 has a frequency band limit of I as described above.
As long as it is within the range of Fo±△F, for example, DC
Since it has a DC output of +5V, the discrimination circuit 23
The fw from 19 is not input to , and the output from 22, for example, DC +5V, is added to it. At this time, at 23, the switch circuit 21 is opened (the state shown in the figure), and the local oscillator VC024 is opened.
△ for adding or subtracting from the immediately preceding control voltage, that is, the voltage of the immediately preceding output voltage polarity of the phase detector 20 at that time.
The voltage of F is also added to the local oscillator VC024. At this time 24
In this case, it is driven to a state shifted to a frequency other than L±ΔF. This is done in order to reduce the level of the external RF signal, which becomes a disturbance wave due to its large level. Note that while the above △V is output from 23,
There is an output from the intermediate frequency detector 22, and the local VC024 is disturbed until the output from the intermediate frequency detector 22 disappears, that is, the influence of the interference wave can be eliminated.

This state corresponds to the case where there is no fw at the input of 23 and there is no output of 22.

An RF signal generator 11 driven by a motor is connected from IFo to I
When Fo + △F, W is input to the input side of the discrimination circuit 23.
There is a state in which there is an output from the intermediate frequency detector 22, and the AFC operation starts again.

Here, just to be sure, the operation of the discrimination circuit 23 is summarized as follows. '1} When there is an fw signal (discrimination signal) and there is an output from the intermediate frequency detector 22, the switch circuit 21 is closed; '2' When there is no fw signal and there is no output from 22, the switch circuit 21 is open. condition, there is no '31fw signal,
When there is an output from 22, 21 becomes connected, and a voltage of 10△V is applied to the local oscillator VC024, and the intermediate frequency detector 2
The frequency of the VCO is IFo + △F until the output of 2 disappears.
Let's just move on.

(Reducing the interference wave Fo). This is in the state of [2}.
Note that within the gain range of the AFC group (24 → 16 → 17) (20 → 21 → 24), normal AFC operation can be performed in the '11 state even if the external RF signal is large. .

As explained above, the present invention modulates the transmitted signal with a known signal, and uses this to perform AFC operation on the receiving side, as well as automatically identify and eliminate interfering signals. It is possible to investigate the frequency characteristics of the line, including the antenna and propagation path, and it is also possible to perform AFC operation that follows RF signals received at a level lower than the interference signal level, so the transmission output level can be reduced. It is possible to make it smaller, and the effect is remarkable.

[Brief explanation of the drawing]

Fig. 1 is a block diagram for explaining the conventional AFC method, Fig. 2 is a block diagram showing an embodiment of the inventive method, Fig. 3 is an input/output waveform diagram of an intermediate frequency tuned detection circuit, and Fig. 4 5 is a diagram showing a specific configuration of the phase detector, FIG. 5 is a diagram showing phase difference versus phase detection characteristics, and FIG. 6 is a diagram for explaining the frequency band range of the intermediate frequency detector. 11... Signal generator, 12... Identification signal oscillator, 13... FM modulator, 14, 15... Antenna, 16... Mixer, 17...・Intermediate frequency amplifier, 18...Intermediate frequency tuning detector, 19...
... Frequency discriminator, 20 ... Phase detector, 1
21... Switch circuit, 22... Intermediate frequency detector, 23... Discrimination circuit, 24... Local oscillation VCO
. Figure 1 Figure 2 Figure 3 Figure 5 Figure 6

Claims (1)

[Claims] 1. A transmission system that frequency-modulates the RF signal using the identification signal fw and sends it out; a mixer that receives the transmission signal from the transmission system and mixes it with the output voltage from the local oscillation VCO;
an intermediate frequency amplifier that converts and amplifies the output signal from the mixer into an intermediate frequency and also serves as a limiter; an intermediate frequency tuning detector that detects the output signal from the intermediate frequency amplifier;
The identification signal fw is determined from the output signal from the intermediate frequency amplifier.
a frequency discriminator that demodulates the frequency discriminator, a phase detector that detects by comparing the phase of the output of the frequency discriminator and the output of the intermediate frequency tuning detector, and a phase detector that detects the output of the intermediate frequency amplifier and also serves as a band limiter. an intermediate frequency detector, an output of the intermediate frequency detector and the identification signal fw as an output of the frequency discriminator;
and a switch circuit that is provided between the phase detector and the local oscillation VCO and turns on and off according to the output of the discrimination circuit. The identification signal fw as the output of the discriminator
The switch circuit is opened and closed in accordance with the output obtained by determining the presence or absence of the intermediate frequency output as the output of the intermediate frequency detector, and the AF is activated without being drawn into interference waves.
AFC using modulated waves characterized by C operation
method.