JPH01320827A - Control system for notch frequency - Google Patents

Abstract

PURPOSE:To avoid notch effect from being lost due to a slight frequency difference by always making the frequency of a disturbed wave coincident with a notch frequency. CONSTITUTION:A frequency of a reference oscillator 33 is set the same as the notch frequency in a local oscillator 3 of a mixer stage 2 placed in front of a notch circuit 1 and a disturbed radio wave is used as a comparison input to a phase detector 32. Then a phase difference output of the phase detector 32 controls the frequency of a voltage controlled oscillator VCO 31 as a control DC voltage through an LPF 34 to constitute a phase controlled oscillation circuit through a path of pre-stage mixer 2 phase detector 32 VCO 31 so that the disturbing frequency applied to the phase detector 32 is equal to the reference frequency (=notch frequency). Thus, the disturbing wave frequency is always made coincident with the notch frequency.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a circuit in a radio receiver having a notch circuit for removing interference waves existing within a pass band.

[Conventional technology]

In a wireless receiver, in order to add only the desired received wave to the demodulator and remove other unnecessary interference waves, the superheterodyne system uses a BPF (pantone or filter) in the intermediate frequency amplification stage. , its passband width is 7 to 15 kHz for DSB (both sideband) waves for broadcasting etc.
z, 2 to 4 for SSB (one side band) for communication
For kHz2%CW (telegraph), interference waves are effectively removed by limiting the frequency to 0.5 to 3 kHz and using a crystal filter or ceramic filter with excellent out-of-band attenuation. However, since amateur radio and small business radio can transmit at any frequency within the permissible band, there is a high possibility that other radio waves will mix into the receiving band. Problems such as image interference, harmonic interference, and spurious beats also occur.

Notch filters have conventionally been used to remove such unnecessary signals within the passband.

These include a series notch, which is used in relatively low-impedance circuits, and which increases impedance at a specific frequency to block the passage of unnecessary signals, and a series notch, which is used in relatively high-impedance circuits, where the parallel impedance decreases at a specific frequency to short-circuit unnecessary signals. There is a parallel notch for absorption, but since the receiver circuit often has high impedance, a parallel notch is usually used. As a notch element for that purpose! : Since the series circuit of C is insufficient, the notch frequency can be adjusted by using the series resonance of a high Q crystal oscillator and adding or subtracting a small series capacitance as shown in Figure 6, so the interfering signal can be removed at the notch. To do this, the interference signal frequency and the notch frequency are matched by adjusting the minute capacitance or by adjusting the local oscillation frequency of the premixer, but if the interference frequency fluctuates,
Even if you fine-tune the tuning of the received wave, if the interference frequency and the notch frequency shift even slightly, the interference wave removal effect will be lost, so you will have to readjust the tuning each time.
Another problem is that the sharper the notch characteristics, the more difficult it is to adjust.

[Problem to be solved by the invention]

As mentioned in the previous section, the sharper the notch characteristic is, the greater the interference wave removal effect is, but there is a problem in that the notch effect is quickly lost even with a slight frequency difference.

The present invention attempts to solve the above-mentioned problems by always drawing the interference waves into the notch frequency.

[Means to solve the problem]

There are two ways to draw interference waves into the notch frequency: to match the notch frequency to the interference wave frequency, and to match the interference wave to the notch frequency. The present invention relies on the latter method of always matching the frequency of the interference wave with the notch frequency.

The present invention is basically as described in claim 1, and to explain it with reference to FIG. It is composed of a VCO (voltage controlled oscillator) 31, a phase detector 32, and 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 as a comparison input to the phase detector 32, 32 The phase difference output passes through the LPF 34 as a control DC voltage to control the frequency of the VCO 31, and the interference wave frequency applied to the phase detector 32 becomes the reference frequency (=
By configuring a phase controlled oscillator circuit through 2→32→31 so that the notch frequency), the interference wave frequency can always be made to match the notch frequency.

The interference frequency applied to the phase detector may be the output of mixer stage 2 divided, multiplied, or frequency converted, and the condition for phase control is to match the interference frequency to the notch frequency by increasing or decreasing the reference frequency at the same rate. holds true.

The range in which the above basic configuration works well is limited. For example, when receiving SSB, the interfering frequency fluctuates, and the oscillation frequency of the VCO 31 moves by that amount to bring the interfering frequency back to the notch frequency. At the same time, the signal frequency also moves by the same amount, so the BFO frequency is changed at the demodulation stage. This results in a deviation from the BFO frequency, making demodulation impossible, resulting in the side effect of having to readjust the BFO frequency.

Therefore, in claim 2, a mixer stage is provided after the intermediate frequency stage 1 having the notch circuit shown in FIG. By supplying the notch frequency to the demodulation stage from the output of the post-mixer, even if there is a shift in the receiving frequency due to fluctuations in the interference wave frequency, it is compensated for in the post-mixer and does not affect the demodulation. The control method is disclosed.

Details of its configuration and operation will be explained in the next example section.

〔Example〕

FIG. 2 shows an example of an implementation configuration in which claim 2 of the present invention is applied to an SSB receiver for amateur radio. In the figure, the same symbol parts as in FIG. 1 are the same operating parts as in FIG. 1.

The received wave is converted to an intermediate frequency of 9000 kHz by the first mixer from the antenna (through a high frequency amplification stage).
This portion becomes a pre-intermediate frequency stage for the notch circuit of the present invention. The output is converted to 455 kHz by pre-mixer 2, passes through notch circuit 1, and is converted back to 9 kHz by post-mixer 4.
000 kHz, passes through a post-intermediate frequency stage, and demodulates the voice using a product detector.

9000 kHz to 455 kHz in premixer 2
The local frequency for converting to z is 9000±455kHz
z, either 8545 kHz or 9455 kHz may be used, but since the sideband frequency relationship is reversed in the latter case, 8545 kHz will be described for convenience of explanation. Next, use postmixer 4 to convert the 455 kHz to the original 900 kHz.
When converting back to 0 kHz, if the local frequency is 8545 kHz, which is common to the premixer,
As the local frequency changes, the intermediate 455k
Although the Hz changes, the pre-intermediate frequency and the post-intermediate frequency do not change at all, and the relationship between the sidebands does not change either. This means that if the pre-intermediate frequency is fl, the post-intermediate frequency is f2, and the local frequency fL, then fl-fL + fL-f2, where (-fL+fL) = 0, so f
If s = f t , it can be proven that Fl and F2 completely match regardless of the change in the local frequency FL. The frequency shift method that uses the above relationship to change the relative position of the filter and the signal is well known among those skilled in the art, but in the present invention, it is used for another purpose, and is shown in FIG. Refer to and explain.

In FIG. 3(A), Fl indicates the band characteristic of a filter with a center frequency of 9000 kHz in the pre-intermediate frequency stage, and 90
00-1.5=8998.5 kHz At the carrier point of the 75KssB signal, 1) the SSB carrier that has been suppressed by about 20 dB is further attenuated by 15 dB or more. Therefore, the SSB signal is approximately 300-2700Hz
Only the upper sideband of the filter is passed and amplified, and the passband width of the filter is approximately 2.4 kHz.

As shown in FIG. 3(B), the frequency converted by the premixer 2 has a center frequency of 455 kHz and a carrier frequency of 453.5 kHz. Now 900 to the prefix intermediate wave stage
If there is an interference wave of 0.5 kHz, the output of mixer 2 will be 455.5 kHz, so by inserting a notch at this frequency, most of the interference wave can be removed.

As shown in FIG. 3(C), the frequency of the post-intermediate frequency stage converted again by the post-mixer 4 is 9000 kHz as the center frequency, 8998.5 kHz as the carrier frequency, and only the remaining interference waves attenuated by the notch are 9000 kHz. It remains at 5 kHz.

The Notch circuit utilizes the series resonance of a crystal resonator, and the electrical equivalent circuit of the crystal resonator Y is shown in Figure 5 (A).
(119, its series resonance frequency is 2xi, Lo is extremely large, co is extremely small, and R is also a small value. Therefore, it is a high value that cannot be controlled by the sharpness of the resonance. It is placed in parallel between the transmission lines to absorb and attenuate only the resonant frequency, but in practice it is shown in Figure 6 (A
), the resonant frequency is finely adjusted by inserting a crystal oscillator YK variable capacitor C8 in series, but since co is an extremely small value, the amount of change in the resonant frequency due to a change in CB is small, and it is 1 at around 455kHz. It is only about kHz. By inserting C8 and inductance L in series as shown in FIG. 6(B), the amount of change can be increased slightly,
It is difficult to completely follow the disturbance frequency when it fluctuates.

In the present invention, the notch frequency is fixed at around 455 kHz (455.5 kHz in FIGS. 2 to 4), and can be easily followed by changing the frequency of the local oscillator 3. Therefore, the constants of the crystal oscillator for the notch do not need to be very strict. However, the notch frequency and the frequency of the reference oscillator 33 must be exactly the same, but fine adjustments can be made on both the notch side and the oscillator side, and the absolute value is not restricted, so it can be matched with a large number of oscillators during mass production. It's easy because all you have to do is make a bear.

The basic oscillation frequency of the phase controlled oscillator is 455.5kHz.
z and the comparison frequency (in this case, the interference wave) is detected by the phase detector 32.
In addition, the phase difference output is integrated by an LPF and used as a DC voltage to control the frequency of the VCO 31. Even if the interfering frequency moves in the wave stage, the output from the premixer 2 to the notch circuit follows the interfering frequency so that it always matches the notch frequency.

The interference wave is 9000±1 at the end of the passband of the front intermediate frequency stage,
Figure 4 shows the frequency relationship when the frequency changes up to 5 kHz. Assuming that the interference wave a moves to the same frequency as the carrier, 8998.5 kHz, the phase controlled oscillator operates so that the frequency of the interference wave a matches the notch frequency of 455.5 kHz at the output of the premixer 2. The oscillation frequency of the VCO 31 is 8998.5-455.5=8543kHz. Therefore, the center frequency is 9000-854.3=457
kHz and 457+8543= for post-mixer 4
Since it is 9000kHz, the carrier frequency is also 455B.
+8543 supplementary 9985kHz completely matches the pre-intermediate frequency.

Also, if the interference wave appears at the opposite band edge at 9001.5 kHz, based on the same principle as above, the oscillation frequency of the VCO 31 will be 9001.5-455.5 = 8546 kHz9, and the center frequency will be 9000-8546 = It becomes 454kHz. The operation of the post-mixer is the same as described above, so a description thereof will be omitted.

Since the interference waves a and b have extreme frequencies, the passband necessary for the notch circuit is [passband a + passband b] in FIG. 4(B), which is 452.5 to 458.5 kl (
It is sufficient to cover the range of z. Since the vCO frequency at that time is 8543 to 8546 kHz, even if there is no interference wave and the phase controlled oscillator is not locked, the VC
If the free run frequency of O31 is set within this range, there will be no problem in reception.

If notch operation is not required, switch the control voltage circuit of the VCO 31 with the switch 34, apply the stabilizing voltage through the voltage regulator, fix the oscillation frequency to around 8545 kHz,
At the same time, the influence of the notch can be completely eliminated by opening the notch circuit or by setting the notch frequency to one position at the end of the passband as shown in FIG. 4 (CB).

When there are two or more frequencies of interfering waves within the band, the most powerful interfering wave is usually locked to the notch frequency. Also SSB
Since the sidebands of the signal are a collection of unspecified frequencies close to noise, they are not locked by this.

〔Effect of the invention〕

In radio receivers, notch circuits are effective in eliminating interference waves within the receiving band, but because the notch element usually uses the series resonance of a crystal oscillator, the variable range of the notch frequency is extremely narrow. Therefore, it is often difficult to match the notch frequency to an arbitrary frequency within the band, and changing the local oscillation frequency of the premixer to match the interfering frequency to the notch frequency may cause the received signal to deviate from its proper position in the band. However, according to the present invention, the notch frequency can be controlled with a relatively simple configuration by applying claim 1 to remove interference waves having a constant frequency relationship. The effects that can be widely used as a notch method for removing arbitrary interference frequencies and greatly fluctuating interference waves by applying Claim 2 are as described in the above [Means for Solving the Problems] and [Example] sections. It is clear that

[Brief explanation of the drawing]

FIG. 1 is a basic configuration diagram of the present invention, FIG. 2 is a block diagram showing an embodiment of an SSB receiver using the present invention, and FIGS. 3 and 4 are each intermediate frequency stage of the circuit in FIG. 2. FIG. 5 is an electrical equivalent circuit of a crystal resonator, and FIG. 6 is a notch circuit of a crystal resonator. 1...notch circuit, 2, 4...mixer, 31...
V.C.O. 32... Phase detector, 33... Reference oscillator. Patent Applicant Yaesu Musen Co., Ltd. No. 1 No. 2 No. 3 No. 9000 KHz No. 5 No. 5 B No. 6 Dry Y

Claims (1)

[Claims] 1. A phase-controlled oscillator is used as a local oscillator in a mixer stage preceding an intermediate frequency amplification stage having a notch circuit for removing interference frequencies; A notch, characterized in that the interference wave frequency is made to match the notch frequency by adding the interference wave output directly or by dividing/multiplying or converting the frequency, and by setting the comparison reference frequency to a frequency corresponding to the notch frequency. Frequency control method. 2. A mixer stage is provided after the intermediate frequency amplification stage having a notch circuit for removing interference frequencies, and a common local oscillation frequency is supplied to the pre-mixer and the post-mixer from the phase-controlled oscillator described in item 1 above. Notch frequency control method.