JPH0420533B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a receiver equipped with a notch filter circuit for removing interference signals appearing near a desired signal.

(Prior Art) FIG. 5 is a block diagram of a receiver using a conventional notch filter circuit. Conventionally, a notch filter is provided whose notch frequency can be changed continuously within the passband, and as shown in Fig. 5, when there is an interfering signal near the desired signal within the receiving passband, the notch frequency of the notch filter is changed. was manually varied to remove the interfering signal as shown in Figure 3a. (In FIG. 3, f _R ′ represents the desired signal frequency converted to an intermediate frequency, and f _N ′ represents the frequency of the interfering signal converted to an intermediate frequency.) (Problem to be solved by the invention) Here, The problem is that in the receiver shown in Fig. 5, the manual controller 8
After removing the interfering signal by adjusting the notch frequency to f _N ', if the desired signal deviates by Δf due to frequency deviation, etc., as shown in Figure 3b, the receiving frequency is finely adjusted by Δf and f _R +Δf is received. Therefore, the reception frequency setter controls the first local oscillator 3 so that the desired signal f _R '+Δf is at the center of the reception passband. Then, as shown in Figure 3c, because the notch frequency does not move within the reception passband (the position indicated by the dotted line), the interfering signal may not be removed or a part of the desired signal may be removed. Become. Therefore, in order to remove the interfering signal, the notch frequency must be adjusted by Δf again (the position of f _N ' indicated by the solid line), which is extremely complicated.

(Means for solving the problems) In order to solve these problems, the present invention has the following features:
When fine-tuning the receiving frequency, the notch frequency is automatically changed by the same amount as the fine-tuning, and the details will be explained below.

(Embodiment) FIG. 1 is a basic block diagram of the present invention. 1
is an antenna, 2 is a high frequency amplifier, 3 is a first local oscillator, 4 is a first mixer, 5 is an intermediate frequency amplifier,
6 is a notch filter, 7 is a notch frequency controller,
8 is a manual controller, and 9 is a receiving frequency setter.

The signal at the reception frequency f _R is mixed with the signal from the first local oscillator 3 by a first mixer 4, amplified by an intermediate frequency amplifier 5, and provided to a notch filter circuit 6 as an intermediate frequency signal f _R '. At this time,
If there is a disturbance signal as shown in Figure 3a,
By setting the notch frequency of the notch filter circuit 6 to _fN ', the interfering signal is removed. The notch frequency f _N ' at this time is set by the manual controller 8 and the notch frequency controller 7, and removes the interference signal as shown in FIG. 3a.

Here, it is assumed that the reception frequency deviates from the current set value f _R by Δf as shown in FIG. 3b. At this time,
By finely adjusting the receiving frequency by Δf, the receiving frequency setter 9 controls the first local oscillator 3 so that the desired signal f _R ′+Δf comes to the center of the receiving passband as an intermediate frequency. At the same time, the reception frequency setter 9 controls the notch frequency controller 7 to shift the notch frequency by Δf. As a result, the notch frequency of the notch filter circuit 6 is as shown in FIG.
This synchronizes with the fine tuning of the receiving frequency, and the interference signal that has been manually removed will be automatically tracked and removed in the fine tuning of the receiving frequency.

Further, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 2 is a detailed block diagram showing one embodiment of the present invention. 10 is a first mixer which converts the desired signal into a 455kHz intermediate frequency signal by mixing it with the first local signal. 11 is the center frequency
A 455kHz bandpass filter defines the aforementioned reception passband. (Here, ±
Set it to 3kHz. ) 12 is a second mixer that converts the intermediate frequency signal into a 100kHz signal using the intermediate frequency signal and the signal supplied from the notch PLL; 13
is a notch circuit with a fixed notch frequency of 100kHz,
14 controls the output of the notch circuit using the output signal of the notch circuit and the signal supplied from the notch PLL.
A third mixer is used to return the frequency to 455kHz, and among the above, the second mixer 12, notch circuit 13, and third mixer 14 correspond to the notch filter 6 in FIG.
is a phase lock loop (PLL for first local) that generates the first local signal, which includes a voltage control generator 151, a phase comparator 152, and a 1/1/2
Consists of N1 frequency divider. 16 is a PLL (for notch) that generates local signals for notch.
PLL) corresponds to the notch frequency controller 7 in FIG.
It shall be possible to vary ±3kHz around 355kHz. 17 is the first microcomputer
Set frequency division numbers N1 and N2 for each frequency divider of the local PLL and notch PLL. It also monitors the reception frequency setting knob 18, notch frequency adjustment knob 19, and notch operation (off, manual, automatic) changeover switch 20.

Next, the state of the signal in each block will be explained, assuming that the desired signal frequency is _fR .

First, a case where there is no interfering signal will be explained. The microcomputer 17 selects the first mixer 1 based on the frequency f _R set by the reception frequency setting knob 18.
0, the frequency division number N1 of the first local PLL 15 is set so that the desired signal is converted to a 455kHz signal. The 455kHz signal is band-limited by a bandpass filter 11, and then passed through a second mixer 12 to a 355kHz signal from the notch PLL 16.
The signal is mixed with the signal, converted to 100 kHz, and supplied to the fixed notch circuit 13. The output of the fixed notch circuit 13 is as shown in FIG. 4a, but since the center of the desired signal is removed by the fixed notch circuit 13, the signal is lowered. Therefore, by turning off the notch operation changeover switch 20, the microcomputer switches the desired signal to 105 kHz because the signal within the reception communication band is not affected by the fixed notch circuit 13, as shown in FIG. 4b. N2 is set in the frequency divider 163 so that the conversion is performed. Then, the signal in FIG. 4b is sent to the notch again by the third mixer 14.
It is mixed with the 350kHz signal of PLL 16, converted to 455kHz, and supplied to the detection circuit.

Next, a case where there is an interfering signal near the desired signal will be described. (Here, set the frequency of the interference signal to
Let f _N. However, 1f _R −f _N1 shall be smaller than 3kHz (1/2 of the passband width). ) The signal outputted from the bandpass filter 11 by operating the reception frequency setting knob 18 is as shown in FIG. 4c.

At this time, the frequency of the interference signal is 455kHz+
( _{fN −fR} ). Subsequently, the signal converted to 100kHz by the second mixer 12 becomes as shown in FIG. 4d. The frequency of the interference wave at this time is 100kHz
+(f _N +f _R ). Next, in order to remove this interference signal, manually operate the notch operation changeover switch 20, and adjust the notch frequency adjustment knob 19 so that the frequency of the interference signal becomes 100kHz.
The output signal of the PLL 16 is assumed to be 355kHz+(f _N −f _R ). At this time, the desired signal frequency is 100kHz−
( _{fN −fR} ). When the interference signal is removed, as shown in FIG. 4e, the signal is mixed with the output signal of the notch PLL 16 again by the third mixer, converted to 455 kHz, and then supplied to the detection circuit.

Next, the frequency of the desired signal is changed as shown in Figure 4 f.
Consider the case where f deviates from _R by Δf. However, Δf is
Must be less than 6kHz (typical bandwidth). or,
The notch changeover switch 20 is set to automatic in order to automatically remove the interfering signal.

When the deviation of Δf is finely adjusted using the reception frequency setting knob 18, the microcomputer 17
As shown in Figure _g , the first local PLL1
Define the frequency division number N1 of 5. At this time, the frequency of the interference wave is 455kHz+{f _N (f _R +Δf)}. Subsequently, it passes through the bandpass filter 11 and is mixed with the notch PLL signal {355kHz+( _fN - _fR ) which was manually set last time] in the second mixer and converted to 100kHz. (Figure 4h) As a result, the frequency of the desired signal is 455kHz + {355kHz + (f _N - f _R )} = 100kHz
+(f _N −f _R )……(1) Similarly, the frequency of the interference signal is 455kHz + {f _N −(f _R −Δf)} = {355kHz
+(f _N −f _R )}=100kHz−Δf……(2). From this equation (2), if the signal of the notch PLL 16 is shifted by Δf, the frequency of the interference signal will be
It can be seen that the frequency is 100kHz.

455kHz + {f _N − (f _R −Δf)} = {355kHz
+(f _N −f _R )−Δf}=100kHz……(3) From this, the microcomputer 17
A frequency division number N2 is set in the frequency divider 163 so that the output of the notch PLL 16 changes by -Δf. The frequency of the signal at this time is 100kHz-( _fN - _fR )+Δf. (Figure 4 i) The signal from which the interfering signal has been removed is
The signal is mixed with the output of the notch PLL 16 by the third mixer 14, converted to 455kHz again (FIG. 4j), and supplied to the detection circuit.

100kHz+(f _N −f _R )+Δf+{355kHz+(f
_N −f _R )−Δf}=455kHz……(4) As explained here, if the notch operation is set to automatic, the interference signal once removed manually will be
Even when the receiving frequency is finely tuned, tracking and removal is automatically performed.

(Effect of the invention) According to the present invention, the interference signal within the reception passband is
Once the notch frequency is manually set, even if the receiving frequency is finely tuned, the notch frequency is automatically tracked and removed without having to adjust the notch frequency again.

[Brief explanation of drawings]

FIG. 1 is a basic block diagram of the present invention, and FIG. 2 is a detailed block diagram of a receiver showing an embodiment of the present invention.
FIG. 3 is an operational diagram for explaining the present invention, FIG. 4 is an explanatory diagram of the operation of the receiver of FIG. 2, and FIG. 5 is a block diagram of a receiver having a conventional notch filter circuit. 3...first local oscillator, 4,10...first
Mixer, 6... Notch filter circuit, 7... Notch frequency controller, 8... Manual controller, 9... Receiving frequency setter, 11... Bandpass filter, 12
...Second mixer, 13...Fixed notch circuit, 14
...3rd mixer, 15...1st local PLL
Circuit, 16... PLL circuit for notch, 17... microcomputer, 18... reception frequency setting knob, 19... notch frequency adjustment knob, 20...
...Notuchi operation changeover switch.

Claims (1)

[Claims] 1. In a receiver equipped with a notch filter circuit in an intermediate frequency amplification stage that removes interference signals that appear near a desired signal, a notch circuit with a fixed notch frequency and a notch circuit provided on the input side of the notch circuit are provided to output a first intermediate frequency signal. a second mixer for converting the second intermediate frequency signal into a second intermediate frequency signal that changes around the notch frequency, and a third mixer provided on the output side of the notch circuit to return the second intermediate frequency signal to the first intermediate frequency signal. A local signal for the notch is generated by controlling the notch frequency by a signal from a manual controller that manually controls the notch frequency, or by controlling the notch frequency by a signal from a receiving frequency setter to change the notch frequency by the same amount as the fine adjustment amount of the receiving frequency. A notch frequency controller that supplies signals of the same frequency to the second mixer and the third mixer, so that even if the receiving frequency is finely tuned, the interfering signal can be removed without adjusting the notch frequency. receiver.