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  • jalves61 6:06 pm on February 27, 2020 Permalink | Reply
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    Object Oriented Programming in C# – Constructors 

    Object oriented programming is an entirely new perspective on programming from procedural programming. It focuses on the manipulation of objects rather than a “top-down” approach. This in general makes object oriented programs easier to modify than procedural based programs. A class is a category of objects which defines common properties of all the objects that belong to it. An object is a self contained entity that consists of data and procedures to manipulate the data.

    In the following snippet of a program, a class “Person” is initialized after the class “Program”. The variables defined within the class are hidden from the parent class unless they are made public. The “perOne” is in instance of a class which is an object.

    prog

    The “Firstname”, “LastName”, etc are properties of each object which are set to different strings.

    A “constructor” is a method with the same name as the class, as shown by the line “Person perOne = new Person()”. The following shows the constructor for the class “Person”

    const

    If a property for “firstname” is not set, when a new object is created that property will default to “unknown” due to the constructor.

     
  • jalves61 4:06 pm on February 26, 2020 Permalink | Reply
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    Keysight ADS – Microstrip Line Design 

    The goal of the project is to design a 50 ohm microstrip line at an operating frequency of 10 GHz and phase delay of 145 degrees.

     

    The following ADS simulation will be composed of four major parts:

    a) Designing the microstrip lines using two models (I.J. Bahl and D.K. Trivedi model and E. Hammerstad and Jensen model). The insertion loss (S(2,1)) will be plotted over the range of 10 MHz to 30 GHz.

    b) Assuming reasonable dielectric losses, results should be compared to part a

    c) Creation of ideal transmission lines with same parameters compared to part a and b

    d) Showing dispersion on the lossless microstrip line. This is compared to the ideal line.

     

    The LineCalc tool (which uses the Hammerstad and Jensen model) within ADS is used to design the second line with the correct specifications. The first circuit is designed using hand calculated values.

    schem

    The following shows using the LineCalc tool to get the values for the second schematic.

    linecalc

    The simulation is shown below.

    sim.PNG

    A new substrate is created with a loss tangent of .0002 for the second schematic. The simulation results in:

    schem2.PNG

    An ideal transmission line circuit is created and compared with both the lossy and lossless lines.

    IL.PNG

    In order to demonstrate dispersion, the phase velocity must be calculated. As shown by the values compared from 0 GHz to 30 GHz, the phase velocity does not change for the ideal line, but does for the microstrip line.

    PV

     

     
  • jalves61 7:52 pm on February 23, 2020 Permalink | Reply
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    Keysight ADS – Frequency Dependence of Microstrip Lines 

    The following ADS simulation will demonstrate how the characteristic impedance and effective dielectric constant change with frequency.  In the simulation, a quarter wave section of multi-layer microstrip line is used to demonstrate frequency effects. The result are expected to show that the dielectric constant and the characteristic impedance are inversely related. When the frequency of the electric field increases, the permittivity decreases because the electric dipoles cannot react as quickly. The multi-layer component is used in place of an ideal component because frequency dependence must be demonstrated. An “MLSUBSTRATE2” component is used with the updated dielectric constant and Dielectric loss tangent.

    schem

    For S parameter analysis, two terminated grounds are required. The effective dielectric constant must be solved for by unwrapping the phase of S(2,1). The results show the characteristic impedance (both real and imaginary parts) increasing with frequency and the dielectric constant decreasing.

    results

     
  • jalves61 6:54 pm on February 21, 2020 Permalink | Reply
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    Keysight ADS – Transient Propagation 

    The following ADS simulation will demonstrate the effects of transients on a transmission line. A rectangular pulse of duration .5 microseconds will be generated and a net voltage vs time will be plotted for a period of .7 microseconds. The circuit has a mismatched load, producing reflections. A time domain reflectometry analysis will prove that the propagating signal voltage steadily increases after the initial time and as time increases, the reflections will eventually die out and leave a steady state response. This is shown with transient analysis.

    schematic.PNG

    The schematic above contains two circuits for the two parts of the rectangular pulse (one with and one without a time delay). The simulated results are shown below.

    res

    A bounce diagram can also be used to convey Time domain reflectometry analysis, as shown below. This diagram is a plot of the voltage/current at the source or load side after each reflection. This is a general diagram and does not apply to the problem.

    bounce.png

     
  • jalves61 11:44 pm on February 19, 2020 Permalink | Reply
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    Acoustics and Sound: Beating 

    Beating is a very important concept in musical instruments. This tremolo-like variation in sound intensity occurs when two pure tones of slightly different frequencies are sounded simultaneously. An experiment can be performed with two tuning forks (one regular and one wrapped with tight rubber bands on the prongs) struck at the same time. The resultant sound intensity will vary, rising and falling periodically. When the sound wave arrives at the ear, the waves initially appear out of phase (destructive interference) then appear in phase (constructive interference). The superposition of the two waves is shown to have a pulsation effect. The frequency of the pulsations is determined by the beat frequency, which is the difference in frequency of the pure tones.

    beating

    The pitch perceived by the ear is the average of the two pure tones. A demonstration can be done with two pipes in an organ (one adjustable pipe). The adjustable pipe is varied within a certain range of the other pipe’s frequency. If the second pure tone is greater than approximately 15 Hz away from the first tone, beating is no longer heard.

     
  • jalves61 5:01 pm on February 18, 2020 Permalink | Reply
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    Keysight ADS – Conjugate Matching 

    This project will use conjugate matching to match a capacitive load of 50-j40 to a generator of impedance 25+j30. Since the generator impedance is complex, conjugate matching is required to match the network, as opposed to in situations of low frequency where the reactive components are negligible. In the example, an L network is used to match the generator to the load. Theoretically, differentiating the power and setting this equal to zero proves that maximum power is transferred when the resistance of the source and load are equal and the reactive portions are equal and opposite phase shift/sign.

    The first step is to use the impedances given to calculate the actual lumped inductor and capacitor values to use for the network to work at 2 GHz. 25+j30 corresponds to a 25 ohm resistor in series with a 2.387732 nH inductor and 50-j40 corresponds to a 50 ohm resistor in series with a 1.98944 pF capacitor.

    The following shows the schematic with the source, matching network and load.

    schem

    Running the simulation with Data Display equations yields….

    maxpower

    This shows maximum power transfer at the correct frequency of 2 GHz. The next step is to use the Smith Chart tool. A shunt inductor and series capacitor is used to form the L Network. Exact values can be typed in for these to get the impedance value Z = 0.5 +j0.6 which is the normalized equivalent source impedance (divided by 50).

    sc

    With the capacitor and inductor values recorded, these values can be loaded into a separate schematic and compared to the original schematic results.

    Conjugate matching is not achieved with this Smith Chart configuration so there is no peak at 2 GHz.

    power

    Alternatively, the Smith Chart tool can be used from the palette. From this point with the chart icon selected, the network can be created by selecting “Update Smart Component” from the Smith Chart tool window. These results show that it is important to select the proper design network for the specifications for optimal results.

    sc.PNG

     

     
  • jalves61 8:32 pm on February 17, 2020 Permalink | Reply
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    Keysight ADS – Quarter Wave Transformer Matching 

    In ADS, a batch simulation can be implemented to run different load impedance simulations. This function will be used to simulate a quarter wave transformer matching system for various loads (25, 50, 75, 100, 125 and 150 ohms),  The system is used to match a 50 ohm line with an electrical length of 60 degrees at 1 GHz.

    The simulation will demonstrate that an unmatched load will generate a constant VSWR at all frequencies. With the implementation of the matching network, the VSWR varies because it is only designed to match the network at a specific frequency. A previous post derived the relationship to find the impedance of a quarter wave matching transformer.

    schem

    The VSWR can be plotted by adding equations into the data display window and manually adding equations into the plot window to plot VSWR against frequency for both the matched circuit and the unmatched circuit. The mismatched circuits appears constant over frequency with a very high SWR, as it does not have the matching transformer. The quarter wave transformer is shown to provide excellent matching at specific frequencies.

    VSWR.PNG

    For batch simulations, a slider tool can be implemented to show only specific impedances. Clicking on the axes and changing the names to include the index will update the plot with the specific impedances one at a time. The plot is updated to match the slider value for the load impedance.

    update.PNG

    With the axes correctly updated, sliding the slider tool will change the plot automatically. Also in the data display window, tables can be added to view specific values at different frequencies.

    table.PNG

     

     
  • jalves61 4:15 pm on February 16, 2020 Permalink | Reply
    Tags: , ECE551   

    Acoustic and Electromagnetic Waves – Problems (Part I) 

    a1a2a3a4a5

     
  • jalves61 11:44 am on February 14, 2020 Permalink | Reply
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    ARRL Examination Study (Part II) 

    For part II of the ARRL examination study, we will study propagation of radio waves.

    Radio waves spread out when transmitted from an antenna in straight lines unless they are reflected or refracted by some object. Due to this spreading and scattering, the waves become weaker as they propagate farther into the air. This limits the “range” a radio transmission can communicate over. The curvature of the Earth creates a “radio horizon” that limits the range of radio propagation. “Line of sight” propagation is when radio waves are transmitted within direct sight of the receiver. This is commonly done in VHF frequencies and higher. Lower frequencies travel as “ground waves”.

    Radio waves are partially reflected when the medium through which the wave propagates changes due to a change in intrinsic impedance (a property defined by permittivity and permeability). Radio waves can even be reflected by change in weather patterns. The figure below shows the concept of diffraction (bending past an obstruction) of radio waves. Diffraction can also refer to spreading when a wave travels through a narrow medium into an open area.

    diffract.PNG

    Light waves also bend by “refraction” which is exactly how radio waves travel around the earth. The earth is curved and therefore the waves need to bend to propagate past “line of sight” distances. The shorter the wavelength (and hence higher frequency), the easier the wave can travel in and out of buildings by penetration of openings in solid objects.

    It interesting to note that different waves received by an antenna can interfere if they are out of phase (destructive interference). This is called “multipath” which is when antennas receive waves from different paths. Moving an antenna a few feet can counterract this. Multipath propagation results in irregular fading. VHF and UHF signals propagating with multipath propagation experience fluttering or “picket-fencing” which comes from rapid variation of the signal strength. Tropospheric propagation or “tropo” is propagation of VHF or higher frequencies assisted by atmospheric phenomena such as weather fronts or temperature inversions. It is not uncommon for Tropo signals to propagate over 300 miles. Reflections can also be caused by conductors such as airplanes. Satellites reflect waves with conductive plating.

    iono

    Thirty to 260 miles above the earth, the ionospheric layer resides. Atoms of nitrogen and oxygen are ionized by UV rays from the sun and become positively charged. The separation of the electrons and the creation of positive ions creates a weakly conductive region. The ionosphere is composed of many different regions. The E, F1 and F2 layers tend to reflect radio waves and the D and E regions tend to absorb waves.

    “Skip” or sky wave propagation is when HF waves are completely bent back towards the earth. The conductive surface of the earth reflects the wave back and the process repeats. These “hops” or reflections allow the waves to be received at farther distances. Lower frequencies are bent more than higher frequencies. For this reason, UHF signals are rarely heard beyond the radio horizon. The MUF (maximum usable frequency) and LUF (lowest usable frequency) are the highest and lowest frequencies that can be reflected by the ionosphere without absorption. When sunspot activity increases, the makes the ionosphere more conductive and increases the MUF.

    Sporadic or “E-Skip” propagation is when patches of the ionosphere become ionized enough to reflect frequencies as high as VHF and UHF. This is most common during early summer and mid winter months.

     

     
  • jalves61 4:26 pm on February 11, 2020 Permalink | Reply
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    Keysight ADS – Short Circuit Terminated Ideal Transmission Line 

    Using ADS, a parameter sweep can be used to confirm the results of a short circuited transmission line. The input impedance of a transmission line is given as

    input.png

    When the line is terminated by a short circuit, ZL = 0 and the equation reduces to only the imaginary part of the numerator. For integer multiples of the wavelength, the input impedance is equal to zero. At odd multiples of a quarter wavelength, the input impedance becomes infinite and looks like an open circuit.

    The following circuit is constructed to test the results. A parameter sweep with the variable theta (the electrical length) is used.

    schem.PNG

    The results are shown below. As expected, the reactance alternates between inductive and capacitive for different electrical length values. The reactance is infinite at quarter wavelength multiples and zero at integer multiples of the wavelength. The current is shown to be lagging the voltage by 90 degrees. The major conclusion to be made is that a transmission line does not behave like a lumped element circuit because voltages and currents are different at different lengths along the line.

    results

     
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