Understanding Filters: Types and Characteristics

Filter Characteristics

• Filters prevent unwanted quantities from passing through a system.
• Car oil filters are a typical example, preventing impurities from entering the engine.
• Electrical filters function similarly, blocking specific frequencies from proceeding to the subsequent circuit stage.
• Filters enable selection of a desired frequency or frequency band, discarding unwanted frequencies.
• Filters find application in channel selection for communications, interference reduction by unwanted frequency rejection, and prevention of spurious oscillations.
• Most electronic devices incorporate at least one filter.
• Filters are categorized based on their frequency response characteristics.

Types of Filters

• Low pass filters:
  • Pass low frequencies.
  • Reject high frequencies.
• High pass filters:
  • Pass high frequencies.
  • Reject low frequencies.
• Band pass filters:
  • Pass a specific range of frequencies.
• Band stop filters:
  • Reject a specific range of frequencies.
• Usually filters pass or reject a band of frequencies rather than a single frequency.
• Band refers to a range of frequencies.

Sound Reproduction and Speakers

• Accurate sound reproduction involves specific speakers.
• Tweeters:
  • Handle high frequencies.
• Mid-range speakers:
  • Handle medium frequencies.
• Woofers:
  • Handle low frequencies.
• Output from the amplifier is fed to the filter card, where the filter splits the audio.
  • High frequencies for tweeters
  • Medium frequencies for mid-range speakers
  • Low frequencies for woofers.
• Only the correct range of frequencies is sent to each speaker.

Low-Pass Filter

• Passes low frequencies.
• Rejects high frequencies.
• The cut-off frequency (fco) is the dividing line between the low and high frequencies.
• Signals below the cut-off frequency:
  • Pass through unaffected.
• Signals above the cut-off frequency:
  • Significantly reduced.

High-Pass Filter

• Passes frequencies higher than a cut-off frequency.
• Rejects frequencies lower than a cut-off frequency.

Aircraft Vibration Sensor

• Filters are used to select frequencies.
• Filters selectively monitor aircraft engine vibration:
  • Rejecting taxi rumble.
  • Rejecting air turbulence.

Basic Filter Operation

• Low pass filters with a cut-off frequency of 1 kHz have different signal outputs at different frequencies.
• 100 Hz signal applied at 10 V peak:
  • The filter allows the signal to pass, but some signal loss may occur due to component configuration.
• 1 kHz signal applied at 10 V peak:
  • Output amplitude is reduced to 7.07 V peak.
  • Attenuation occurs within the filter, output voltage reduces even before reaching the cut-off frequency.
• 10 kHz signal applied at 10 V peak:
  • Filter reduces the amplitude of the output to 1 V peak.

Practical Filters

• Ideal filters in the shaded area of the ideal curves, pass frequencies.
• Ideal filters in the unshaded area, reject frequencies.
• Ideal filters are selective, cutting off output voltage or starting sharply at the cut-off frequency, resulting in a sharp distinction between passed and rejected signals.
• Practical filters introduce gradual attenuation or loss with frequency, unattainable steep and selective curves.
• Output voltage gradually decreases as frequency increases beyond the cut-off in a practical low-pass filter response, increasing attenuation incrementally at a constant rate.

RC Low-Pass Filter

• RC low-pass filter uses a series resistor and a shunt capacitor.
• Also an attenuator:
  • The output is nearly always less than the input.
• Output voltage varies with frequency:
  • Inductors and capacitors are frequency sensitive.
• Inductive reactance (XL) :
  • Proportional to frequency.
• Capacitive reactance (XC) :
  • Inversely proportional to frequency.
• Capacitive reactance (XC) is high at low frequencies:
  • Most of the input voltage appears across the capacitor.
• XC decreases as frequency increases:
  • More voltage appears across the resistor.
  • Less voltage appears across the capacitor.

RL Low-Pass Filter

• Uses a series inductor and a shunt resistor.
• Inductive reactance (XL) varies:
  • Proportionately with frequency.
• At low frequencies, XL is very low:
  • Most of the input voltage appears across the resistor.
• As frequency increases, XL increases:
  • More voltage appears across the inductor.
  • Less appears across the resistor.
• This circuit rolls off the higher frequencies.

Summary of Low-Pass Filters

• An RC low-pass filter will perform the same task as an RL low-pass filter with the same cut-off frequency.
• The roll-off rates will also be the same.
• RC low-pass filters:
  • Typically less expensive and easier to use.
• Capacitors :
  • More cost-effective.
  • Greater range of values
  • Generally smaller than inductors.

Introduction to High-Pass Filter Operation

• Passes all frequencies above the cut-off frequency with little or no attenuation.
• Rejects signals below the cut-off frequency.
• Easily constructed with various combinations of resistance, capacitance and inductance.

RC High-Pass Filter

• Has a series capacitor and a resistor forming a voltage divider.
• The filter output is taken from across the resistor.
• At frequencies below the cut-off frequency:
  • Capacitive reactance (XC) is very high, and most of the generator voltage will be across the capacitor.
  • Very little voltage appears across the output resistor.
• As the frequency increases, Xc decreases.
  • Less voltage is dropped across the capacitor.
  • More voltage appears across the resistor, allowing the higher frequencies to pass.

RL High-Pass Filter

• Has a series resistor and an inductor forming a voltage divider.
• Output voltage is taken from across the inductor.
• Below the cut-off frequency:
  • Inductive reactance (XL) is very low.
  • Most of the generator voltage will be across the resistor.
  • Very little voltage will appear across the output inductor.
• As the frequency increases, XL increases.
  • Less voltage is dropped across the resistor.
  • More voltage appears across the inductor, allowing the higher frequencies to pass.
• The output of an RC high-pass filter at the cut-off frequency (fco) is 70.7% or 3 dB down from the maximum applied voltage.
• Performance of RC and RL high-pass filters is typically identical.
• Above the cut-off frequency, high-pass filters pass signals with little attenuation.

Summary of High-Pass Filters

• Performance of RC and RL high-pass filters:
  • Generally identical,.
• Above the cut-off frequency:
  • Both RC and RL high-pass filters pass signals with little attenuation.
• At the cut-off frequency:
  • The attenuation will be 3 dB.
• Below the cut-off frequency:
  • The attenuation increases at a rate of 6 dB per octave or 20 dB per decade, as in RC and RL low-pass filters.
• RC and RL low- and high-pass filters are made with various combinations of:
  • Inductors.
    • Capacitors.
    • Resistors.
• Filters are a voltage divider:
  • One is a resistor.
  • The other is a frequency - varying component, such as an inductor or a capacitor.

Output Voltage and Frequency

• Output voltage is tapped from a voltage divider is less than the input voltage.
• Output voltage varies:
  • Supply frequency changes.
  • Circuit reactance changes.
  • Voltage division ratio changes.
• By selecting resistance and capacitance for the voltage divider:
  • Filters are designed to pass/eliminate desired frequencies.

Series Resonance

• Inductive and capacitive reactances in an LCR circuit vary with frequency.
• The condition in which the inductive reactance equals the capacitive reactance is called resonance.
• For every L&C combination:
  • There is just one frequncy, in both series and parallel circuits, that causes XL to exactly equal Xc,
  • This is known as the resonant frequency.
• Series or parallel circuit is fed the resonant frequency:
  • XL becomes equal to Xc.
  • The circuit becomes resonant:
  • Totally resistive.
  • Circuit is tuned.

Circuit Operation

• Curves show how XL and Xc vary with frequency in a series resonant circuit.
• Resonant frequency (fr) is where the magnitude of XL equals the magnitude of Xc.
• Below the resonant frequency (fr):
  • Xc is larger than XL.
• Voltage across the capacitor is larger than the voltage across the inductor.
• The series LCR circuit will act capacitively.
• Above the resonant frequency (fr):
  • XL is larger than Xc, so voltage.
  • Voltage across the inductor will be larger than the voltage across the capacitor.
• Series LCR circuit act inductively.

Parallel Resonance

• The resonant frequency (fr) of a parallel resonant circuit is calculated with the same formula used for series resonant circuits:
  • fR = 1 / (2π√(LC) )
• In an ideal parallel resonant LC circuit the source voltage is applied across each component.

Tuned Circuits

• An LCR circuit has the ability to separate frequencies.
• An LCR circuit responds;
  • Differentiates resonant frequency from other frequency.
• LC 'tuner':
  • Divides frequencies.
  • Picks resonant frequency.
  • Rejects other frequencies.
• Tuner:
  • Selects desired station: -.Rejects all other stations.
• Frequency change:
  • Tunes the resonant circuit.
  • Selects another station.
• At resonance in a series resonant circuit, the impedance :
  • Resistive.
  • Low value:
  • The value of the resistance of the wire in the coil.
• In a parallel resonant circuit (tank circuit), at resonance, the impedance:
  • Resistive.
  • High value:
  • Depending on the values of L and C, can be almost infinite.

Resonant Circuits as Filters

• Resonant circuits can be made to serve as filters.
• Series LC circuits (resonant) offer:
  • Minimum opposition to current flow at frequencies at or near resonant frequency.
  • Maximum opposition to current flow at all other frequencies.
• Parallel LC circuits (resonant) offer:
  • Maximum opposition to current flow at frequencies at or near resonant frequency.
  • Minimum opposition to current flow at all other frequencies.
• These concepts construct band-pass and band-stop filters.
• Band-pass filters:
  • Two common types of filters that use resonant circuits.
• Band-stop filter:
  • Two common types of filters that use resonant circuits.

Band-Pass Filter

• Use resonant circuits.
• Designed to pass/reject narrow frequency range :
  • Widely used.
  • Communication/navigation equipment.
• Allows:
  • Selected range of pass.
  • Frequencies attenuated:
    • Above this range
    • Below this range
• Two configurations for a band-pass filter
  • Series resonant LC network.
  • Parallel resonant LC network.

Simple Band-Pass Filter

• Series LC circuit:
  • Acts as a band-pass filter.
  • Passes currents:
  • Frequencies are at to near its resonant frequency.
  • Opposes passage of frequencies.
  • Frequencies are outside this band.
• Parallel-LC circuit:
  • Tuned at same frequency:
    • Series LC circuit
  • It will produce the most direct line of current, which is the same frequency band outside of the series resident circuit
  • Provides a path for all currents:
    • Frequencies are outside the limits.
    • Frequency band passed.
    • Series-resonant circuit.
• Series LC:
  • Minimum Imepdance
  • Passes max current
  • Resonance
• Parallel-LC circuits:
• Max impedance:
  • Resonance
  • Minimun current: passing
• Simplest Form
• Two LC circuits:
  • Two LC circuits connection creates simplist form from the shown view (c)
  • Two LC circuit limits:
  • Action filter
  • Filter cut points.

Combination series-parallel band-pass filter

• Series LC resonant circuits:
  • Offer minimum impedance at resonance.
  • Passing maximum output
• parallel LC resonant circuits
  • offer maximum impedance at resonance.
  • passing minimum current.
• Frequencies:
  • Not within selected bandwith
  • Delivery will result in the LC Blocking -Shunt will block them away from the LOAD

Band-Stop Filter

• Blocks are attenuates signal: -Narrow Frequency Range
• Notch:
  • Band elimination
• Band Pass Filters has two basic configurations for A band-stop filter:
• Series Resident LC Newtork
• Parellel Resonate LC network
• All frequency's
• Above-Below band

Simple Band Stop Filters

• Blockage Narrow Frequency
• Current allows all frequencies.
• Direction opposite has been obtained, positions of filter interchanges are made:
  • A has blocking has been Act in Current:
• View B frequency -Can be for band for rejected can obtain for the simplest

Summary

• Resonant Series LC Circuits offer Minimum impedance for current
• Passes Max Current
• Resident
• Parellel LC Circuits of the the the Max impedance
• Minimums the current to pass the all the bandwidth
• Frequency is the most important because of all the signal and its pass of and shun out will

AC Generator Theory

• AC Generator - Electrical power : - Used onboarded from aircrafts is CA-Result is CA: Result AC all generators its the MOST imp
  • The load power that has supply is the CA.
• AC the CA alternators are hydroelectric are tremendous at High power are very low - Alternator - Potential is 12-v
• EMF will induced by colie as Cutting result or MAgnet colie
• CA generator the Relative station between conductor station

Alternator Types

• There are 2 alternate:
  • Revolivng armature is the stator for the field - Rotor is the field - Most Aircrafts will the the

CA generator operation

• Similar - By slip AC - In electric no high used with is in large Quantity's - Ring outputs is VIA AC output Ring

Rotating-Field Alternators

• High -Voltage AC ( is Quality type
  • High Voltage-High Amperage-Low Range

Permanent magnet Alternators

• PMGS,EDAS-PMS - The rate is Proportional - PM/AC is an OUTPUT

brushless Operation

(no requiring to power the supplied)

• No required to power the the power supplied (field supply brushes or slip(the depended to that ) - Operate the voltage-current

Generator CA

• Generator Field:
• Seperate magnet -Permanent Magnetic Magnet - exciter

Sine wave generator (CA)

• Is that each wave can - Alternation during (moment the Time) - In 360 rotation of loop the sinusoidal wave

Ac power with cycle CA motor

• CA power with circle CA motor that has direction -terminal/ voltage The Ac with electrons from one/both directions

Alternator Phase Types

- single Phase-Continuosly 
   - Volatge: Alternate - known as:
        - Single phase Alternate 

• Stator( winding armature) (is seriess for add-AC) to a voltge In mathematical analysis the Phase is Represent by:
  • ∅ CA
  • Power(portable tools
    • However(from alternattors single)

Three-phase alternator

• (2 or more in the single) the phases are single( wind are symmotrilly to the CA) Thesere will be Electric(the Other CA(desgined to produce to seprate single)

Two-Phase, Three-Wire Alternator

Now, look at the smaller schematic diagram in bottom left corner. A two-phase alternator connected in this manner is called a two-phase, three-wire alternator.

Three or PolyPhase alternate

• There are Three or Most Aircrafts; -120 degrees-any one(from 2)

3- ∅ Star and Delta Connections

• In The side of the out in from have will three-phase

• WYE- Connected value -Neutral

  • Neutral is The A/to /c-Singles

• DELTRA conncet- end to end.

Formular CA power:

To will consume this:

√3 × Volats × ampere