JPH0478210A - Automatic frequency control method for notch filter or band eliminate filter - Google Patents

Abstract

PURPOSE:To stabilize a frequency to be eliminated of a filter by correcting the deviation of the eliminating frequency automatically on each occasion when the eliminating frequency of a notch filter or a band eliminate filter is deviated. CONSTITUTION:A filter 1 consists of a coil and a capacitor and a varactor element such as a variable capacitor diode in which the capacitance C is varied with an applied voltage is employed for the capacitor. A branching device 2 is used to branch part of signals passing through the filter 1. A band pass filter 3 extracts only a signal of a prescribed frequency band from the signal extracted by the branching device 2. An amplifier 4 amplifies the signal passing through the filter 3 and a detector 5 detects a signal outputted from the amplifier 4. A comparator 6 compares a signal from the detector 5 with a preset reference frequency signal, discriminates whether or not the input frequency is deviated from the reference frequency and applies a voltage to the varactor diode of the filter 1 so as to correct the deviation when the frequency is deviated from the reference frequency.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The method of automatically removing the frequency side of a notch filter or band emitting filter of the present invention is used, for example, in a CATV system to remove specific frequencies such as spurious signals. When the removal frequency of a notch filter or a band eluminate filter deviates due to temperature changes, etc., the deviation can be automatically corrected.

(Prior Art) In the conventional notch filter or band eluminate filter, the removal frequency was set by manually controlling the inductance of the coil and the capacitance C of the capacitor.

[Problems to be Solved by the Invention] In conventional notch filters or band eluminate filters, C changes due to temperature changes, and the preset removal frequency may shift. To correct this deviation, C must be readjusted as described above. However, conventional glue and C adjustments have to be done manually, which is time-consuming, and requires the casing in which the coils, capacitors, etc. are housed to be opened.

(Object of the Invention) An object of the present invention is to adjust the frequency of the notch filter or band elluminate filter so that when the removal frequency of the notch filter or band elluminate filter deviates due to temperature changes, the deviation is automatically corrected. The object of the present invention is to provide an automatic control method.

(Means for Solving the Problems) As shown in FIG. 1, the frequency automatic control method for a notch filter or band elluminate filter of the present invention uses a variable capacitance element whose capacitance changes depending on the applied voltage in the filter 1. , the same filter], and detects whether the frequency of the signal deviates from a preset frequency. If it deviates, the voltage applied to the variable capacitance element is Change, filter 1
The invention is characterized in that the removal frequency is automatically corrected each time by the amount of the deviation.

(Function) In the frequency automatic control method of the non-chip filter or the band eluminate filter of the present invention, when the removal frequency of filter 1 deviates, the deviation is automatically corrected each time, so that the removal frequency of the filter is always constant, and only desired frequencies can be removed.

(Embodiment) FIG. 1 shows an embodiment of the method for automatically controlling the frequency of a notch filter or band emitting filter according to the present invention, in which the filter 1 is a notch filter.

The filter 1 shown in FIG. 1 is composed of a coil and a capacitor, and a variable capacitance element such as a varicap diode whose capacitance C changes depending on an applied voltage is used as the capacitor.

Reference numeral 2 in FIG. 1 is a splitter, which branches part of the signal that has passed through the filter 1.

Reference numeral 3 in FIG. 1 is a bandpass filter, which extracts only signals in a predetermined frequency band from the signal extracted by the splitter 2.

Reference numeral 4 in FIG. 1 is an amplifier for amplifying the signal passed through the band-pass filter 3, and reference numeral 5 is a detector for detecting the signal output from the amplifier 4.

6 in Fig. 1 is a comparator, which compares the signal input from the detector 5 with a preset reference frequency to determine whether the frequency deviates from that frequency. Filter 1 to correct the deviation.
This applies voltage to the variable capacitance diode. The capacitance C of the variable capacitance element to which the voltage is applied changes according to the applied voltage, and the removal frequency of the filter 1 is automatically adjusted to a predetermined value.

(Effects of the Invention) According to the present invention, when a deviation occurs in the removal frequency of a notch filter or a band emitting filter, the deviation is automatically corrected each time.
The removal frequency becomes stable.

It is also convenient because there is no need to open each case that houses the coils and capacitors and manually adjust them.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the automatic filter frequency control method of the present invention. ■ is a filter

Claims (1)

[Claims] In notch filters or band emitting filters that remove specific frequencies, those filters 1
A variable capacitance element whose capacitance changes depending on the applied voltage is used to extract a part of the signal that has passed through the filter 1, detect whether the frequency of the signal deviates from a preset frequency, and detect the deviation. A notch filter or band eluminate, characterized in that when the voltage applied to the variable capacitance element changes, the removal frequency of the filter 1 is automatically corrected by the deviation each time. Automatic filter frequency control method.