JPS5839416B2 - monitor receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a monitor receiver (described in detail below).

In the United States and other countries, a lot of information, mainly news, is transmitted outside the general broadcast band whenever it becomes available.

Such broadcasts are called P, S, B (Public Service Broadcasting), and their carrier frequencies are 30 to 50 MHz (LOW VHF band).

FM signals of 150 to 170 MH2 (HIGHvHF band) and 450 to 470 MHz (UHF band) are widely used in firefighting, security, highway patrol, weather forecasting, etc.

Also, such broadcasts are not transmitted all the time, but are broadcast intermittently only when transmitting information.

Also, broadcast frequencies are typically allocated at intervals of 30 KHz.

The device that receives such broadcasts is a monitor receiver, and conventionally, the oscillation circuit of the monitor receiver is configured so that a crystal oscillator can be selectively inserted and replaced. The channels are grounded automatically or manually to switch channels and receive the desired broadcast.

There are various types of monitor receivers, from 4 channels that can receive 4 stations to 8, 10, 12, and 16 channels, and each hL
OW VHF B: / C, HIGHVHF band, U
There are those for exclusive use of the HF band, and those for multiple bands that are a mixture of these bands.

FIG. 1B is a block diagram of a 3-band, 4-channel monitor receiver and a specific circuit diagram of band switching means.

In Figure 1, ANT, ANT2 are antennas for VHF band and UHF band, respectively, and 4 and 5 are LOW V
A high frequency amplification circuit and a first mixing circuit that constitute the high frequency amplification stage 1 for the HF band, 6 and 7 a high frequency amplification circuit and the first mixing circuit that constitute the high frequency amplification stage 2 for the HIGHVHF band, and 8 and 9 the UHF A high frequency amplification circuit and a first mixing circuit constituting the high frequency amplification stage 3 for the band, each of the high frequency amplification circuits 4, 6, 8 and the first mixing circuit 5,
7.9 is selectively supplied with operating power by band switching means U.

The local oscillation means that supplies the local oscillation output (local oscillation injection voltage) to the first mixer 5, 7.9 for each band generates a basic oscillation signal determined by the crystal oscillators X1 to X4, and outputs the basic oscillation signal. An oscillator U is connected to the oscillator U, which is supplied to the first mixer 5 for the LOW VHF band via the line 11, and the frequency of the oscillation output derived from the oscillator is multiplied by three times, and the multiplied output is connected to the line. 13 through the H
The first to be supplied to the first mixer 7 for IGHVHF band
connected to the first stage frequency multiplier 14 and the oscillator 12 [
connected in parallel with the first first-stage frequency multiplier 14], and generates a multiplied output that is slightly different from the multiplied output of the first first-stage frequency multiplier 14 in response to the oscillation output of the oscillator. A second first-stage frequency multiplier 14' is cascade-connected to the second first-stage frequency multiplier 14' and multiplies the frequency of the output of the multiplier by three times [9 times the fundamental oscillation signal]. death,
A second frequency multiplier 16 supplies the frequency multiplied output to the first mixer 9 for the UHF band via a line 15.

17 is a first intermediate frequency stage (intermediate frequency amplifier) for amplifying the first intermediate frequency signal (frequency 10.7 MHz) from the first mixer 5, 7°9 for each band; 18 is a second intermediate frequency amplifier;
In the mixer, the first intermediate frequency signal and the oscillation signal from the second local oscillator 19 are added to the second mixer 18 to create a second intermediate frequency signal (frequency 455 KIIz).

20 is a filter circuit, and the output of this circuit is transmitted to the next stage, the second intermediate frequency stage.

21 is a clock pulse generator consisting of an astable multi-by-break, etc.; 22 is a counter, decoder, etc.;
23 is a diode switch circuit, LED
1 to LED4 are light emitting diodes for channel display.

The electrical performance required for a monitor receiver is desirable to have good reception sensitivity and selectivity characteristics, and to be strong against interference signals, but the relationship between sensitivity and interference is contradictory and it is generally difficult to achieve good performance in both.

Furthermore, if the broadcast waves are adjacent to each other and a strong electric field occurs, this will create bad conditions for the receiver.

Furthermore, in the receiver shown in FIG. 1, the reception band of each channel is selected by band selection switch circuits S, ~S4 constituting the band switching means U, and the channel in which the crystal oscillator is inserted is selected. Regardless of whether
No matter which channel is swept and switched, power is always supplied to the high frequency amplification circuit and the first mixing circuit of one of the bands and they are in operation.

Therefore, in this type of monitor receiver, there is a risk that the following malfunctions may occur.

(I) Undesired broadcast signals are received even on channels where a crystal resonator is not inserted.

(I) When receiving the desired broadcast signal on a channel in which a crystal oscillator is inserted, interference occurs due to interference from other signals.

The present invention aims to provide a monitor receiver that completely prevents the malfunction (I) among the above malfunctions.

Before explaining the present invention, let us consider the causes of the above-mentioned malfunction.

First, as the cause of (I), (a) the second local oscillation circuit 19
When the following equation holds between the harmonics of the frequency (second local oscillation frequency fo2) and the broadcast frequency (fs) arriving at the antenna.

(However, n and m are positive integers, IFl is the first intermediate frequency,
■F2 is the second intermediate frequency.

) (b) Two or more strong electric field signals arrive,
■F1. ■If F2 is possible.

That is, when the following formula holds true.

(However, fu1fu2 is an undesired broadcasting signal frequency.) As mentioned above, double super is disadvantageous due to (a), but it can be seen that even single super is not completely absent due to (b).

Therefore, as a countermeasure against the malfunction in (1), In the case of (a) ■ Make the power injected into the second local oscillator 19 the minimum practical power.

■ Lower the harmonic content of the second local oscillator 19 as much as possible.

■ Shield the 2nd station 19.

In the case of (b), (2) use FETs (dual gate FETs are better) as transistors in the high frequency amplifier circuit and the first mixing circuit;

■ Add an AGC circuit to the high frequency amplifier circuit.

■ Emitter grounded surface for emitter of high frequency amplifier circuit.
Insert a 100g resistor.

(However, the noise figure increases.

)■ Lower the gain of the high frequency amplifier circuit and mixing circuit.

■ Increase the load Q of the tuning circuit.

Although measures such as these were taken, it was not possible to completely eliminate malfunctions in (I).

Therefore, in the present invention, when the receiver is sweep-switched to a channel in which a crystal oscillator is not inserted, for example, the 10B voltage of the high frequency amplifier circuit, first mixing circuit, second local oscillation circuit, etc. that constitute the front end section is The malfunction described in (I) above is completely prevented by shutting off and disabling these circuits and completely stopping reception of channels in which no crystal resonator is inserted.

Note that the purpose of the present invention is not to prevent the above-mentioned malfunction (n), so explanations regarding the causes and countermeasures for the above-mentioned malfunction (II) will be omitted.

Next, the present invention will be explained with reference to FIGS. 2 to 4.

FIG. 2 is a block diagram of the monitor receiver of the present invention,
In FIG. 2, the first local oscillation frequency amplification circuit 24,
A circuit 25 that converts the first local oscillation frequency into a DC voltage, and a switching circuit 26 that receives the DC voltage of the circuit 25 as an input.
, three new circuits have been added.

Furthermore, in Fig. 2, the presence or absence of a crystal oscillator, that is, the presence or absence of an oscillation signal from the crystal oscillator, is detected using a new circuit such as this.
Switching transistor Q7 t Qs tQo constituting band switching means Ly and second local oscillation circuit 19
Turn on the power.

I am trying to control it to OFF.

A specific circuit example of the operation is shown in FIG.

FIG. 3 shows a concrete circuit of the glue and parts 24 to 26 in FIG. 2.

In Figure 3, the transistor Q of the first local oscillation circuit U
, is grounded, an oscillation frequency fo is generated in the transistor Q1, the oscillation output is taken out at the 0 point, and the oscillation output is sent to the amplification transistor Q2. Q3. It is amplified by Q4 and applied to the frequency-voltage exchange transistor Q.

Here, is a varistor for temperature compensation of the transistor Q, and VR is a variable resistor for setting the threshold voltage of the transistor Q.

If the input signal fo is now input to transistor Q, transistor Q is turned on, and the collector potential (0 point potential) of transistor Q is lowered.

Conversely, when the fo input signal does not enter transistor Q, the collector potential of transistor Q increases.

Since the next stage transistor Q6 becomes a 0-point inverter, when the fo signal is generated, that is, in the channel where the crystal resonator is inserted, the transistor Q6 is turned on and the collector potential of the transistor (0-point potential) goes up.

()9 level. ) On the other hand, when the fo signal is not generated, that is, in a channel in which no crystal resonator is inserted, the transistor Q6 is turned off, and the collector potential of the transistor is lowered.

(It becomes low level.) The power supply is turned on and off by the collector potential of transistor Q6 in Fig. 4.
F-controlled band switching means and second local oscillator circuit 1
9 is a specific circuit diagram.

As mentioned above, in the channel where the crystal resonator is inserted, the collector potential of the transistor Q6, that is, the switching transistor Q7. Q8. The emitter potential of Q9 is high.
level, so the switching transistor whose base is grounded, that is, the switching transistor corresponding to the set band of the channel being swept, is turned on.
Power is then supplied to the high frequency amplification stage of the corresponding band.

On the other hand, in the channel in which the crystal resonator is not inserted, the switching transistor Q7. Q8. Since the emitter potential of Q9 becomes low level, all the transistors are OF.
F, and no power is supplied to the high frequency stage of any band.

Similarly, in the second local oscillation circuit 19, power is supplied to channels in which a crystal resonator is inserted, and power is not supplied to channels in which a crystal resonator is not inserted.

In this embodiment, an example is described in which the receiver is used in a 3-band double superheterodyne monitor receiver.
It goes without saying that the present invention is not limited to this embodiment, and may be used, for example, in a one-band single superheterodyne monitor receiver.

Furthermore, when a channel in which a crystal oscillator is not inserted is selected (when it is the turn of the sweep), not only the high frequency amplification stage and the second local oscillation circuit are disabled, but also the intermediate frequency amplification stage is disabled. The broadcast signal may be prevented from being received by disabling circuits such as the low frequency amplification stage and the low frequency amplification stage.

As described above, the monitor receiver according to the present invention disables at least one of the signal transmission circuits from the high frequency amplification stage to the low frequency amplification stage when a channel in which a crystal oscillator is not inserted is selected by sweep. As a result, it is possible to completely prevent a malfunction in which an undesired broadcast signal is received on a channel in which a crystal resonator is not inserted.

[Brief explanation of drawings]

Figure 1A2 shows a block diagram of a conventional monitor receiver and a specific circuit connection diagram of the band switching means, Figure 2 is a block diagram of a monitor receiver according to the present invention, and Figures 3 and 4. 2 is a detailed circuit connection diagram of the main part of FIG. 2. L2, 3...High frequency amplification stage, 4, 6, 8...
...High frequency amplification circuit, 5, 7, 9...First mixing circuit, 19...Second mixing circuit, 24...
...First local oscillation frequency amplification circuit, 25...Oscillation frequency-voltage exchange circuit, 26...Switching circuit controlled by the presence or absence of an oscillation signal, X, ~X4.
·····Crystal oscillator.

Claims (1)

[Claims] 1. In a monitor receiver that uses a plurality of crystal oscillators corresponding to predetermined broadcast waves as tuning elements and sequentially sweeps and switches the crystal oscillators, no crystal oscillator is inserted. A circuit is provided that disables at least one of the signal transmission circuits from the high-frequency amplification stage to the low-frequency amplification stage when a channel is selected, and broadcast signals are received in channels where a crystal oscillator is not inserted. A monitor receiver characterized in that: 2. When a channel in which a crystal resonator is not inserted is selected, a circuit that disables at least one of the signal transmission circuits from the high-frequency amplification stage to the low-frequency amplification stage depends on the presence or absence of the oscillation signal from the crystal resonator. The monitor receiver according to claim 1, characterized in that it is a controlled circuit. 3. The monitor receiver according to claim 1, wherein the power to the high frequency amplification stage and the second mixing circuit is cut off when a channel in which no crystal oscillator is inserted is selected.