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A narrow band pass filter audio presentation

2015-01-10 02:13  
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This article is a narrow band pass filter the audio presentation. To grasp this principle more effective, the proposed combination of text read schematics. Audio sideline tee or headphone output from a VHF / UHF scanning or communication receiver is connected to the input of the bandpass filter. Band-pass filter output to connect a digital frequency meter (DFM), and / or audio monitor speaker. The use of a monitor speaker tw1eaking filter's resonant frequency. If a DFM, will not be using the computer program, such as Spectroscopy Laboratory for spectral display TV Video airlines on the computer screen. Tuning range from ~ 400 Hz filter is 4 KHz, 50 KHz when using a potentiometer. Adjustment of the filter is usually resonate around 1000 - 1300 Hz. This frequency range corresponds to the maximum output level of 2.4 KHz USB mode. A 10 k trimmer also added (not shown in the schematic). This may include in the series with the main boiler 50 k. I do this in my filters, and the central tuning range is from 300 Hz to 1000 Hz to move to the band broadening and increasing by a factor of about 4 times up to 2 kHz. A trim pot useful for the receiver, the most low-key actor step 100 Hz, for example, the International Council of Museums R7000/7100/8500 so on. Initially, an LM348 op amp is used in circut. While this work is good, is found by replacing LM348 with LM6134BIN IC, improve the high frequency response has been. Please note that only a single integrated circuit for band-pass circuits. Four amplifier circuit is indicated on the diagaram all contained in a single integrated circuit. The circuit is simple but effective. 


bandpass filter Narrow band audio bandpass filter
Part list:

(1) 50K linear dual-gang potentiometer.

(1) 10K linear dual-gang potentiometer (optional fine tune control).

(2) .1 uf ceramic capacitors.

(1) .01 uf ceramic.

(2) .01 uf greencap capicitors.

(2) .1 uf monoceramic capacitors.

(2) 5.6K resistors.

(2) 10K resistors.

(3) 11K resistors.

(1) 120K resistor.

(1) 1M ohm resistor.

(1) LM6134BIN op-amp IC,OR: (1)  LM348  (or similar) op-amp.

Note: all resistors are 1/4 watt, metal film 1% tolerence.Bandpass filter Schematic without extra amplification (only three op-amps used)    Biquad filter. A close relative of the state variable filter,is showm below. This circut uses three op-amps. It has the interesting property that you can tune its frequency (via the single double-gang pot) while maintaining constant bandwidth(rather than constant Q).