JPS6239710B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention includes an attenuator for attenuating a received Loran signal, and an apparatus that automatically adjusts the gain of the Loran signal amplification circuit in the Loran receiver in order to keep the output of the amplifier circuit constant. The present invention relates to a gain control device for a Loran receiver having an AGC (automatic gain control) circuit for controlling the gain.

Loran navigation, a type of hyperbolic navigation, uses a Loran receiver on a ship to receive pulses of the same period alternately transmitted from a pair of Loran transmitting stations, and measures the arrival time of both pulses. It is a method of navigation to know the position of one's own ship.

Generally, the transmission power from the Loran transmitting station mentioned above is set very high, but since there is a limit to the dynamic range of the input side of the Loran receiver on a ship, when approaching one of the transmitting stations, the Loran receiver cannot be expected to behave correctly.

Therefore, an attenuator is inserted before the receiver to lower the level of the Loran wave reception signal,
At that stage, a method that performs normal signal processing is exclusively adopted.

In addition, the measurement of arrival time difference in Loran navigation is
Since it is necessary to precisely superimpose the received pulses of each of the main station and slave station inside the receiver, it is necessary to keep the output signal amplitude of the amplifier circuit of each received signal constant at all times.
Therefore, an ordinary Loran receiver is also provided with an AGC circuit that automatically controls the gain in the amplifier circuit so that the amplitude of the output signal is constant.

Of these, the AGC circuit must be operated at all times, but due to its nature, the attenuator only needs to be inserted before the amplifier circuit when the ship approaches the transmitting station and the reception level becomes excessive. Therefore, the conventional Loran receiver has an attenuator 1 as shown in FIG.
The amplifier circuits 2 are configured to operate individually, and in many cases, the attenuator is turned on or off as appropriate using a manual switch 3.

However, with such a device, manual operation is required to turn on attenuator 1 when the ship approaches the transmitting station, and turn off attenuator 1 when the ship is a certain distance away. At the moment when the state is reversed, the input voltage of the amplifier circuit changes rapidly, so the operation of the AGC circuit is unable to follow this change, and the output of the amplifier circuit becomes discontinuous at least for the time that the tracking is delayed, making it impossible to measure the time difference. There were shortcomings that had a serious impact on the

Therefore, the main purpose of this invention is to
Focusing on the fact that both AGC circuits have a common function of increasing and decreasing the gain of the entire receiver, it automatically sets the appropriate on-off state of the attenuator according to the position of the ship, and To provide a gain control device that does not require any manual operation and automatically readjusts the amplifier circuit so that the total gain of the receiver does not change discontinuously every time the state of the receiver is reversed. .

To summarize the present invention, a gain control device for a Loran receiver includes an attenuator that can selectively set two states of on and off, an amplifier circuit that amplifies a Loran wave received signal, and an AGC circuit. an attenuator on-off control circuit that reverses the state of the attenuator when the gain of the amplifier circuit reaches a predetermined constant value when the amplifier is in a constant state;
The present invention is characterized in that it includes an AGC changing means that changes the magnitude of the gain control signal so that when the attenuator is inverted, the receiver overall gain fluctuation due to the inversion is compensated by the amplifier circuit.

The constant value of the gain of the above amplifier circuit is, for example,
AGC when the attenuator is off and the received signal becomes strong to the limit of the amplifier circuit's dynamic range.
It is defined as the gain value of the amplifier circuit reduced by the action of the circuit, and conversely the amplification increased by the action of the AGC circuit when the attenuator is in the on state and the received signal becomes considerably weak. It is defined as the gain value of the circuit.

In the embodiments described below, it is assumed that a constant value of the gain of the amplifier circuit is predetermined as the above gain value.

FIG. 2 is a block diagram of an automatic gain control device which is an embodiment of the present invention.

First, the configuration of this device will be described. A Loran wave signal received from an antenna 5 is introduced into an attenuator 7 via an antenna coupler 6. This attenuator 7 is an attenuator that has two states, an on state and an off state, and either state is selected by an attenuator on-off control circuit to be described later. The received signal that has passed through the attenuator 7 is then introduced into the amplifier circuit 8, where an envelope wave of an appropriate level necessary for the next stage time difference measuring section (not shown) is formed. It is assumed that this amplifier circuit 8 also includes a detection circuit and the like.

On the other hand, the AGC circuit for keeping the output signal of the amplifier circuit 8 at a constant level includes an AGC detector 9 that detects an increase or decrease in the gain of the amplifier circuit 8 based on the level of the output signal from the amplifier circuit 8, Vessel 9
an AGC value circuit 10 that sets a gain control amount based on as a digital amount; and this AGC value circuit 1.
It is composed of a DA converter (digital-to-analog converter) 11 that converts the output of 0 into an analog quantity and supplies it to the amplifier circuit 8 as a gain control signal.
If the AGC circuit is made into a digital control system with the AGC value circuit 10 as its main body, the gain control amount for the amplifier circuit 8 can be handled as a digital value, and as a result, gain control can be performed accurately and easily. can. Incidentally, the AGC detector 9 detects the gain increase/decrease of the amplifier circuit 8 by generating a sample pulse in the frequency divider 12 and using this pulse to set a detection point on the envelope output from the amplifier circuit 8.

Since the AGC circuit has this configuration,
The gain control amount set in the AGC value circuit 10, i.e.
The gain of the amplifier circuit 8 increases or decreases as the AGC value increases or decreases.

Next, the attenuator on-off control circuit 13:
A control circuit that turns on or off the attenuator 7 according to the magnitude of the AGC value set in the AGC value circuit 10, and when the attenuator 7 is in the on state and the AGC value reaches a predetermined upper limit value. Shifting the attenuator 7 to the off state, and conversely, when the attenuator 7 is in the off state,
When the AGC value reaches a predetermined lower limit value, the attenuator 7 is turned on. Moreover, this control circuit 13
When the state of the attenuator 7 is reversed as described above, the adder/subtracter 14 is simultaneously activated to change the AGC value. That is, the adder/subtractor 14 corresponding to the AGC changing means of the present invention functions as an AGC control circuit, and when energized by the control circuit 13,
In order to compensate for the receiver total gain fluctuation caused by the inversion of the attenuator 7 in the amplifier circuit 8, the AGC value circuit 1
Change the AGC value that is set to 0 by directly adding or subtracting it. Therefore, when the attenuator 7 changes from the on state to the off state, the AGC value is subtracted so that the increased gain becomes the decreased gain of the amplifier circuit 8, and conversely, when the attenuator 7 changes from the off state to the on state, the AGC value is subtracted so that the increased gain becomes the decreased gain of the amplifier circuit 8. When the state changes, the AGC value is added so that the decreased gain becomes the increased gain of the amplifier circuit 8.

By doing this, it is possible to prevent the overall gain of the receiver from changing suddenly immediately after the state of the attenuator 7 is reversed, and the overall gain of the entire receiver changes linearly. .

For ease of understanding, the operation of this device will be further explained in detail with reference to FIG.

FIG. 3 is a diagram illustrating the gain state inside the receiver according to the movement of the ship.

In the figure, region (A) shows the gain fluctuation state when the ship moves away from the transmitting station, and region (B) shows the gain fluctuation state when the ship approaches the transmitting station. Also, area (1)
and (4) indicate that the attenuator 7 is in the on state, and regions (2) and (3) indicate that the attenuator 7 is in the off state.

The vertical axis corresponds to the gain of the amplifier circuit 8
Indicates AGC value. Note that the solid line (a) shows the gain of the amplifier circuit, and the broken line (b) shows the overall gain of the receiver.

Now, suppose that the AGC value and the gain of the amplifier circuit are in a proportional relationship, and when the AGC value is 1000, the gain of the amplifier circuit is
Assume that there is 100dB. Also, the attenuation amount of attenuator 7 is
30dB.

Initially, if the receiver turns on the attenuator 7 because the reception level in the initial state is high, then as the received signal becomes weaker, the gain in the amplifier circuit is increased.

Then, when the gain of the amplifier circuit reaches 80 dB, which is the upper limit value in this state, that is, the AGC value reaches 800, the attenuator on-off control circuit 13 detects this and shifts the attenuator to the OFF state.

At this time, the AGC value is simultaneously calculated by the adder/subtractor 14.
300, so that the gain of amplifier circuit 8 is reduced by AGC
A value of 300 would result in a reduction of 30dB.

Subsequently, as the received signal becomes weaker, the gain of the amplifier circuit 8 increases while the attenuator 7 remains in the off state.

The transition of the gain state of the amplifier circuit 8 and the overall gain state of the receiver due to the above operation is shown in the area (A) in Figure 3.
is shown. As is clear from the figure, the gain increase due to turning off attenuator 7 corresponds to
It can be seen that by directly reducing the AGC value, it is ignored, and as a result, the overall gain shown by the broken line (b) changes linearly.

Similarly, in region (B), when the received signal gradually becomes stronger and the amplifier circuit gain, which is the lower limit value in this state, reaches 40 dB, that is, the AGC value reaches 400, the attenuator on-off control circuit 13 switches the attenuator 7 from off to on, and at the same time, the adder/subtractor 14 switches the AGC
Add 300 to the value 400, which corresponds to a gain of 30dB.

As a result, the gain reduction caused by turning on the attenuator is ignored by directly adding the corresponding AGC value, and the total gain in region (B) in Figure 3 also changes linearly. I understand.

Note that the attenuator on-off control circuit 13 can determine the upper and lower gain limits of the amplifier circuit 8 when the attenuator 7 is in a constant state, and the upper and lower limit values can also be set. It is also easy to use the control circuit 13.

Also, in the above explanation, 300 is the addition/subtraction value of the AGC value.
It is assumed that is set in advance in the adder/subtractor 14 as a fixed value. Of course, this value can also be easily set to an arbitrary value.

Furthermore, this device is provided with a manual gain adjustment circuit 15 so that the AGC value, that is, the gain of the amplifier circuit 8 can be arbitrarily changed manually.

By the way, as shown in Fig. 3, there is a difference of 10 bB between the point where the attenuator 7 changes from on to off and the point where it changes from off to on.
A hysteresis width of 10 dB is provided for the following reason.

First of all, the amount of attenuation by an attenuator is not necessarily constant due to element errors, and for the same reason, the relationship between the AGC value and the gain of the amplifier circuit is not necessarily constant. As a result, even with the same attenuator and the same amplifier circuit, there are some receivers in which the overall gain does not change linearly.Secondly, if there is no hysteresis width, a certain input This is because the attenuator constantly turns on and off under signal strength, and the overall gain no longer fluctuates smoothly.

By providing a hysteresis width, these can be compensated to some extent.

For ease of understanding, in the above example,
It is assumed that the AGC value and the gain of the amplifier circuit are in a proportional relationship, but if they are not, the AGC value subtraction value when the attenuator transitions from on to off, and the AGC value when the attenuator transitions from on to off. It is necessary to make the added values different.

Although not shown in FIG. 2, it is actually desirable to provide a circuit for switching between master station reception and slave station reception.

As detailed above, according to the present invention, the attenuator is automatically turned on when the received signal is strong, and the attenuator is automatically turned off when the received signal is weak. Since the receiver overall gain fluctuation due to state reversal is compensated at the same time by the amplifier circuit 8, the gain of the amplifier circuit when the attenuator is reversed to the on or off state is determined by the dynamic range range of the amplifier circuit. By setting within 100 kHz, the overall gain of the receiver can always be in the best condition regardless of the condition of the received signal, and the overall gain will be discontinuous immediately after the attenuator is turned on or off. Since it is possible to prevent the total gain from changing, and to make the fluctuation of the total gain linear, it is possible to eliminate the negative influence on the time difference measurement.

Further, if the automatic gain control device according to the present invention is applied, the attenuator is turned on and off as appropriate depending on the received signal, so there is an effect that the dynamic range does not need to be expanded more than necessary.

[Brief explanation of the drawing]

FIG. 1 shows a partial block diagram of a conventional Loran receiver, FIG. 2 shows a main part block diagram of an automatic gain control device for a Loran receiver, which is an embodiment of the present invention, and FIG. FIG. 2 is a diagram illustrating the operating state of the automatic gain control device shown in FIG. 2; 1, 7... Attenuator, 2, 8... Amplifier circuit, 9...
...AGC detector, 10...AGC value circuit, 13...
Attenuator on-off control circuit, 14... Adder/subtractor.

Claims (1)

[Claims] 1. An attenuator that allows the Loran wave reception signal from the antenna to pass through as it is in the off state and attenuates and passes it in the on state, an amplifier circuit that amplifies the output signal from the attenuator, and A gain control device for a Loran receiver comprising an AGC circuit that controls the gain of the amplifier circuit by forming a gain control signal to keep the output of the amplifier circuit constant, when the attenuator is in a predetermined state, When the gain of the amplifier circuit reaches a predetermined constant value, the attenuator is turned on to reverse the state of the attenuator.
When the off control circuit and this attenuator are inverted, the magnitude of the gain control signal is changed so that the above amplifier circuit can compensate for the receiver overall gain fluctuation due to the inversion.
An automatic gain control device for a Loran receiver, characterized by comprising AGC changing means.