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  • jalves61 9:23 pm on March 26, 2020 Permalink | Reply
    Tags: Communications,   

    RFID – Radio Frequency Identification 

    RFID is an important concept in the modern era. The basic principle of operation is simple: radio waves are sent out from an RF reader to an RFID tag in order to track or identify the object, whether it is a supermarket item, a car, or an Alzheimer patient.

    RFID tags are subdivided into three main categories: Active, passive and semipassive. Active RFID tags employ a battery to power them whereas passive tags utilize the incoming radio wave as a power source. The semipassive tag also employs a battery source, but relies on the RFID reader signal as a return signal. For this reason, the active and semi passive tags have a greater range than the passive type. The passive types are more compact and also cheaper and for this reason are more common than the other two types. The RFID picks up the incoming radio waves with an antenna which then directs the electrical signal to a transponder. Transponders receive RF/Microwaves and transmit a signal of a different frequency. After the transponder is the rectifier circuit, which uses a DC current to charge a capacitor which (for the passive tag) is used to power the device.

    The RFID reader consists of a microcontroller, an RF signal generator and a receiver. Both the transmitter and receiver have an antennas which convert radio waves to electrical currents and vice versa.

    The following table shows frequencies and ranges for the various bands used in RFID

    RFIDtable

    As expected, lower frequencies travel further distances. The lower frequencies tend to be used for the passive type of RFID tags.

    For LF and HF tags, the working principle is inductive coupling whereas with the UHF and Microwave, the principle is electromagnetic coupling. The following image shows inductive coupling.

    inductive coupling

    A transformer is formed between the two coils of the reader and tag. The transformer links the two circuits together through electromagnetic induction. This is also known as near field coupling.

    Far field coupling/radiative coupling uses backscatter by reradiating from the tag to the reader. This depends on the load matching, so changing the load impedance will change the intensity of the return wave. The load condition can be changed according to the data in order for the data to be sent back to the reader. This is known as backscatter modulation.

     
  • mbenkerumass 10:02 am on November 27, 2019 Permalink | Reply
    Tags: Communications, , , RADAR   

    Doppler Effect 

    RF/Photonics Lab
    November 2019
    Michael Benker

     

    Doppler Effect

                    The Doppler Effect is an important principle in communications, optics, RADAR systems and other systems that deal with the propagation of signals through space. The Doppler Effect can be summarized as the resultant change to a signal’s propagation due to movement either by the source or receiving end of the signal. As the distance between two objects changes, so does the frequency. If, for instance, a signal is being propagated towards an object that is moving towards the source, the returning signal will be of a higher frequency.

    260px-Dopplerfrequenz

    The Doppler Effect is also applied to rotation of an object in optics and RADAR backscatter scenarios. A rotating target of a radar or optical system will return a set of frequencies which reflect the distances of each point on the target. If one side of the target is moving closer while the other side is moving away, there will be both a higher and lower frequency component to the return signal.

    Dopplereffectsourcemovingrightatmach0.7

     
  • mbenkerumass 4:35 pm on November 9, 2019 Permalink | Reply
    Tags: Communications,   

    Angle Modulation 

    RF/Photonics Lab UMASS Dartmouth
    November 2019
    Michael Benker

    Angle Modulation

    In comparison to Amplitude Modulation, which varies the magnitude of the sinusoidal carrier wave, Angle Modulation varies the phase of the carrier wave. The two most common forms of angle modulation are phase modulation (PM) and frequency modulation (FM). Phase modulation varies the instantaneous angle linearly with the message signal, while frequency modulation varies the instantaneous frequency with the message signal. The signals on the right are understood (from top to bottom) as the carrier frequency,the modulating wave and the result signal of amplitude modulation, phase modulated and frequency modulation. Due to phase modulated and frequency modulated waves having constant amplitude AC, noise is expected to be lower, although the transmission bandwidth is increased.Rates of distortion are reduced with a reduced possibility of a polarity shift. The average power for angle modulated wave is Pave=(1/2)*(AC)2.The table below summarizes the relationship between phase-modulated and frequency-modulated waves. An FM wave can be seen as a PM wave with a substitution of the integral of the message signal for the message signal. Further, an FM wave can be represented as having gone through an integrator while a PM wave is represented as having gone through a differentiator.

    The benefits of conserving bandwidth lead to the development of the narrow-band frequency modulation scheme. To achieve this, several parameters are defined. The frequency deviation, or the maximum departure of the instantaneous frequency from the carrier frequency is defined as Δf = kfAm, where kf (as mentioned in Table 4.1) is the frequency sensitivity factor.The modulation index, β is the ratio of the frequency deviation to the modulation frequency: β = Δf/fm. The angle of the FM wave and the FM wave itself are described as: The following block diagram depicts a method for generating a narrow-band FM wave:Carson’s rule defines an approximate relation for the transmission bandwidth of an FM wave generated by a single-tone modulating wave. From the following expression(Carson’s rule), it is understood that large values of the modulation index β the bandwidth is slightly greater than the twice the frequency deviation Δf and for small values of the modulation index, the spectrum is limited to the carrier frequency and a pair of side-frequencies at fc± fm, in which case the bandwidth approached 2*fm.

    anglemodulation

    angle1angle212349fm

     
    • Jared 11:28 pm on November 9, 2019 Permalink | Reply

      Phase modulation is a bit tougher to understand for me than frequency modulation. Awesome post

      Like

      • mbenkerumass 5:59 am on November 10, 2019 Permalink | Reply

        For phase modulation, I think one way to understand it is to think of the effects we talk about using transmission lines. Depending on the length of the line in comparison to the wavelength, there is a phase shift on the output. This is a type of phase modulation. It would be interesting to ask Dr. Gendron about that one.

        Like

  • mbenkerumass 7:11 pm on November 6, 2019 Permalink | Reply
    Tags: Communications, ,   

    Frequency Shift Keying 

    ECE471 – Communication Theory, Professor Dr. Paul Gendron
    November 2019
    Michael Benker
    Frequency Shift Keying

    300px-Fsk.svg

    The following MATLAB code simulates Frequency Shift Keying, an essential part of Communications.

    fsk1fsk2

     

    inclass20191105

     

     
  • mbenkerumass 12:48 am on October 9, 2019 Permalink | Reply
    Tags: Communications, ,   

    MATLAB Simulation: Voltage Control Oscillator 

    ECE471 – Communication Theory, Professor Dr. Paul Gendron
    October 2019
    Michael Benker
    Voltage Control Oscillator MATLAB Simulation, Integral to Costa’s Receiver

    voltagecontroloscillatorsim

     
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