JPH084237B2 - Receiving machine - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiver circuit having a notch circuit for removing an interfering wave existing in a pass band in a radio receiver.

[Conventional technology]

In the radio receiver, only the desired received wave is added to the demodulator, and in order to remove other unnecessary interference waves, the super heterodyne system has a BPF (bandpass filter) in the intermediate frequency amplification stage and its pass band. Width is DS for broadcasting etc.
7 to 15 kHz for B (both sideband) waves, SSB for communication
2-4kHz for (one sideband), 0.5 for CW (telegraph)
Limiting to ~ 3kHz, by using a crystal filter or ceramic filter with out-of-band attenuation, it is effective in removing the interference wave. However, in amateur radio and small business radio, it is possible to transmit at any frequency within the allowable band, so it is not uncommon for other radio waves to be mixed into the reception band. In addition, problems such as image interference, harmonic interference, and spurious beat mixing occur.

A notch filter has been conventionally used to remove such an unnecessary signal in the pass band. This includes a series notch that increases the impedance at a specific frequency using a relatively low-impedance circuit and blocks the passage of unwanted signals, and the parallel impedance drops at a specific frequency used by a relatively high-impedance circuit to short-circuit unwanted signals. Although there is a parallel notch that absorbs, the parallel notch is typically used because the receiver circuit has a high impedance. Since a series circuit of L and C is not sufficient as a notch element for that purpose, the series resonance of a high Q crystal unit is used.
As shown in the figure, the notch frequency can be adjusted by adjusting the minute capacitance in series.Therefore, in order to remove the interference signal with the notch, the minute capacitance can be adjusted or the local oscillation frequency of the premixer can be adjusted to reduce the interference signal. The frequency and the notch frequency are made to match, but if the interfering frequency fluctuates or the tuning of the received wave is finely adjusted and the interfering frequency and the notch frequency deviate even a little, the effect of removing the interfering wave disappears. It is necessary to adjust each time, and the sharper the notch characteristic is, the more difficult the adjustment is and the more the notch frequency shifts.

[Problems to be Solved by the Invention]

As described above, the sharper the notch characteristic is, the greater the interference wave removing effect is, but there is a problem that the notch effect is rapidly lost even if there is a slight frequency difference.

The present invention is intended to solve the above-mentioned problems by always drawing the interfering wave into the notch frequency.

[Means for solving the problem]

There are two methods of pulling the interference wave to the notch frequency: adjusting the notch frequency to the interference wave frequency and adjusting the interference wave to the notch frequency. The present invention is performed by the latter method of always matching the frequency of the interference wave with the notch frequency. That is, referring to FIG. 1, the local oscillator 3 of the mixer stage 2 preceding the intermediate frequency amplification stage 1 having a notch circuit is a VC.
O voltage controlled oscillator 31, consisting of a phase detector 32, a reference oscillator 33, if the reference oscillation frequency is set to be the same as the notch frequency, and the interference radio wave is used for comparison input to the phase detector 32,
The phase difference output of 32 passes through LPF34 and becomes a control DC voltage, and VCO
By configuring the phase-controlled oscillator 3 that passes through the premixer 2-> phase detector 32-> VCO 31 so that the interference frequency applied to the phase detector 32 by controlling the frequency of 31 becomes (reference frequency = notch frequency), Make the jammer frequency always match the notch frequency.

The interfering frequency applied to the phase detector 32 may be the output of the premixer stage 2 divided / multiplied or frequency-converted,
The phase control condition for matching the jamming frequency with the notch frequency by increasing or decreasing the reference frequency at the same rate is satisfied.

When the radio wave format is SSB reception, the interfering radio frequency fluctuates, the oscillation frequency of the VCO 31 moves by that amount, and if the interfering frequency is returned to the notch frequency, the signal frequency also moves at the same amount, so Since there is a deviation from the BFO frequency at the demodulation stage and demodulation is impossible, the side effect is that the BFO frequencies must be adjusted again. Therefore, the rear mixer 4 is provided in the intermediate frequency stage having the notch circuit 1, and a common local oscillation frequency is supplied from the VCO 31 to the front mixer 2 and this rear mixer 4, and the rear mixer output is supplied to the demodulation stage. By the supply, the notch frequency control is configured so that even if the reception frequency moves due to the fluctuation of the interfering radio frequency, it is compensated by the rear mixer 4 and does not affect the demodulation.

〔Example〕

FIG. 2 is a block diagram showing an embodiment of the SSB receiver using the present invention. In the figure, the same symbol parts as in FIG. 1 are the same operation parts as in FIG.

The received radio waves are converted from the antenna (through the high-frequency amplification stage) into the intermediate frequency of 9000 kHz by the first mixer, and this portion is a front intermediate frequency stage for the notch circuit of the present invention. This output is converted to 455kHz by the front mixer 2, converted to 9000kHz again by the rear mixer 4 through the notch circuit 1, and the output is demodulated by the product detector through the rear intermediate frequency stage. ing.

Since the local frequency for converting 9000 kHz to 455 kHz in the front mixer 2 is 9000 kHz ± 455 kHz, 8545 kHz
, And 9455kHz, but in the latter case, the sideband frequency relationship is reversed, so a simple explanation of 8545kHz will be described.

Next, when converting the 455 kHz back to the original 9000 kHz with the rear mixer 4, the local frequency is the same as that of the front mixer.
When 8545kHz is used, when the local frequency changes, the intermediate 455kHz changes accordingly, but not only the front intermediate frequency and the post intermediate frequency do not change at all, but also the sideband relationship does not change. . This means that the front intermediate frequency is f ₁ , the rear intermediate frequency is f ₂ , and the local frequency is
if f _L is _{f 1 -f L + f L =} f 2, regardless where _{(-f L + f L) =} 0 a is from f ₁ = f _2, and the how to change the local frequency F _L , F ₁ and F ₂ can be proved to be an exact match. The frequency shift method for changing the relative position of the filter and the signal by utilizing the above relationship is well known to those skilled in the art, but is used for another purpose in the present invention. FIG. 3 is a diagram showing a pass band when passing through the intermediate frequency notch circuit. FIG. 3 (A) shows the band characteristic of the filter with the center frequency 9000 kHz of the pre-intermediate frequency f ₁ , 9000−1.5 = 8998.5 (kHz) is the carrier point of the SSB signal, and the SSB signal is in the upper side of 300-2700 Hz. Only sideband is amplified. The passband width of this filter is about 2.4 kHz.

The frequency converted by the front mixer 2 has a center frequency of 455kHz and a carrier frequency of 453.5k as shown in Fig. 3 (B).
Hz. If there is a 9000.5kHz interfering wave in the pre-intermediate frequency stage, the output of the mixer 2 is 455.5kHz, so a notch of this frequency can be inserted to remove most of the interfering wave. The frequency of the rear intermediate frequency stage converted again by the rear mixer 4 is the center frequency as shown in FIG. 3 (C).
9000kHz, carrier frequency 8998.5kHz, interference wave is attenuated at the notch, and only the rest remains at 9000.5kHz.

The notch circuit utilizes the series resonance of the crystal unit, and the electrical equivalent circuit of the crystal unit Y is shown in FIG.
(B), the series resonance frequency is , L _o is extremely large, C _o is extremely small, and R _o is also a small value, which indicates the sharpness of resonance. Is a few thousand or more, which is a high value that cannot be obtained with other elements, so it is inserted in parallel between transmission lines to absorb and attenuate only the resonance frequency. However, in practice, it is shown in FIG. 6 (A). As shown in, the variable capacitance C _s is put in series with the crystal unit Y to finely adjust the resonance frequency, but since C _o is an extremely small value, C _s
The amount of change in the resonance frequency due to the change in is small, only about 1kHz near 455kHz. Although it is possible to slightly increase the amount of change by inserting C _s and the impedance L _s ′ in series as shown in FIG. 6 (B), it is difficult to completely follow up when the interference frequency changes.

In the present invention, the notch frequency is around 455 kHz (see FIGS. 2 to 4).
The frequency is fixed to 455.5 kHz in the figure) and the frequency of the local signal phase control oscillator 3 is changed to easily adjust the intermediate frequency of the jamming radio wave to the frequency of the notch circuit. Therefore, the constant of the notch crystal unit does not need to be so strict. However, the notch frequency and the frequency of the reference oscillator 33 must be exactly the same, but both the notch circuit 1 and the reference oscillator 33 can be finely adjusted, and the absolute value is not restricted. It's easy because you can form a matching pair with.

The basis of the phase-controlled oscillator 3 is to add a reference frequency of 445.5 kHz and a comparison frequency (in this case, an interfering wave) to the phase detector 32,
The phase difference output is integrated by the LPF to control the frequency of the VCO31 as a DC voltage, and the VCO31 is locked when the interference frequency and the reference frequency match.Therefore, the interference frequency moves in the front intermediate frequency stage. However, the output from the premixer 2 to the notch circuit 1 follows so that the interference frequency always matches the notch frequency.

9000 ± 1.5kHz at the end of the pass band of the front intermediate frequency stage
FIG. 4 shows the frequency relationship in the case of changes up to. If the disturbing wave a moves to 8998.5 kHz, which is the same as the carrier, the phase control oscillator 3 operates so that the frequency of the disturbing wave a coincides with the notch frequency of 455.5 kHz at the output of the front mixer 2, and the oscillation frequency of the VCO 31 Is 8998.5−455.5 = 8543kHz. Therefore, the center frequency is 9000-8543 = 457 kHz, and the rear mixer 4 has 457 + 8543 = 9000 kHz, so the carrier frequency is also 455.5 + 8543 = 8998.5 kHz, which is exactly the same as the front intermediate frequency.

Also, if the interfering wave b is output at 9001.5kHz at the opposite band end, the oscillation frequency of VCO31 is 900
1.5−455.5 = 8546kHz, center frequency is 9000−8546
= 454kHz. The operation of the post-mixer is the same as that described above, so a description thereof will be omitted.

Since the disturbing waves a and b are both extreme frequencies, the pass band required in the notch circuit is [pass band a in FIG. 4 (B)].
+ Pass band b], and it is sufficient to cover the range of 452.5 to 458.5 kHz. VCO frequency at that time is 8543 ~ 8546k
Since the frequency is Hz, even if the phase-controlled oscillator 3 is not locked due to the absence of an interfering wave, setting the free-run frequency of the VCO 31 within this range will not cause any trouble in reception.

If notch operation is not required, the control voltage circuit of VCO 31 is switched by switch 34 and a stabilizing voltage is applied through a voltage regulator to fix the oscillation frequency to around 8545kHz and open the notch circuit at the same time, or If the notch frequency is located at the pass band edge as in (1), the effect of the notch can be completely eliminated.

When there are two or more frequencies in the band, the most powerful one is usually locked at the notch frequency. Also, SSB
The sidebands of the signal are a set of unspecified frequencies close to noise, so they are not locked by this.

〔The invention's effect〕

In the radio receiver provided with the notch circuit, in the present invention, the premixer is provided in the preceding stage of the notch circuit, and the local signal supplied to the premixer is equal to the output of the premixer and the frequency of the notch circuit. The frequency input to the notch circuit is the notch frequency by using the output of the phase-controlled oscillator that controls the oscillation frequency of the VCO with the DC voltage that passes through the LPF and the phase detection is performed by the phase detector that can be adjusted. Since the output of the premixer always holds the notch frequency even if the interference wave frequency changes and the interference wave frequency changes, it is particularly effective for an interference wave with a frequency change. Also, SSB
For reception, a post-mixer stage is provided after the notch circuit and the same local signal as that of the pre-mixer is supplied, so that demodulation is not hindered, and therefore the utilization effect is great.

[Brief description of drawings]

FIG. 1 is a block diagram of the basic configuration of the present invention, FIG. 2 is a block diagram of an embodiment of an SSB receiver using the present invention, and FIG.
4 and FIG. 4 are diagrams showing the frequency relationship of each intermediate frequency stage of the circuit of FIG. 2, FIG. 5 is an electrical equivalent circuit of a crystal oscillator, and FIG. 6 is a notch circuit of a crystal oscillator. 1 notch circuit, 2, 4 mixer, 3 phase control oscillator, 31 VCO, 32 phase detector, 33 reference oscillator, 34 changeover switch.

Claims (1)

[Claims] 1. A super-heterodyne receiver having a second intermediate frequency circuit provided with a notch circuit, wherein the notch circuit comprises a crystal filter having a frequency close to the second intermediate frequency, and a notch operation occurs when a notch selection switch is turned on. The frequency control of the VCO oscillator that supplies a local signal to the premixer in the preceding stage of the notch circuit consists of a fixed voltage circuit for converting to a normal intermediate frequency and the oscillation of the output of the premixer equal to the notch frequency. The circuit that detects the phase by the phase detector by the output of the frequency reference oscillator and outputs it through the LPF is configured by the switch that works in conjunction with the notch selection switch, and there is an interfering radio wave in the received signal. When the selection switch is turned on, the second intermediate frequency shifts so that the interference wave becomes the notch frequency, and the interference wave is generated by the notch circuit. Receiver characterized in that it is attenuated.