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  1. Z

    Phantom resistors

    hi guys I am attempting to solve a problem that has me scratching my head. I have a small connector PCB with one 8k resistor present. The connector is four way with the resistor terminals being the two inner pads. The outer two pads are short circuit together. I solder two wires on the...
  2. Z

    Speed of sound in vortical flows

    hi there I am currently working with linear flows and using a ultrasonic setup to determine the speed of sound in a linear gaseous flow. But I would like to know more about the speed of sound in a vortical flow. Unfortunately I haven't been able to find any good book with regard to my topic...
  3. Z

    Fourier transform of a lorentzian function

    hi I know the Fourier transform of a lorentzian function is a lorentzian but i was wondering if the Fourier transform of the second derivation of a lorentzian function is also a second derivative of a lorentzian function Thanks
  4. Z

    Solving a first order differential equation

    hi the differential equation i am attempting to solve is: \frac {dP} {dx} = \frac {gP} {1+P/Psat} here is what I have done: \frac {dP} {dx} = \frac {gP*Psat} {Psat+P} divide both sides by \frac {Psat+P} {gP*Psat} to get: \frac {Psat+P} {P*Psat} \frac {dP} {dx} =g...
  5. Z

    PAM signal with a cosine input

    sketch the spectrum of the PAM signal S(f) if the input is m(t)=cos(2*pi*fm*t) where fm=3000 at a sampling rate of 10000 using rectangular pulses of duration 0.04ms. in the range +-15Khz S(f)=H(f)*M'(f) taking the Fourier transform of the rectangular pulse we obtain: H(f)=Tsinc(Tf) where...
  6. Z

    What does normalization mean?

    ok thank you will look into it
  7. Z

    What does normalization mean?

    what does normalization mean? for example say i have the guassian input as : A(0,T) = \sqrt{Po}*exp(-T^2/2To^2) then we can normalize it by defining t=T/To and A(z,T) = \sqrt{Po}U(z,t) Po= peak power t= normalized to the input pulse width To. if the peak of the pulse is...
  8. Z

    Difficult project decision

    Hey guys, I have a good job lined up for me after I graduate with a good company, i am currently 8 months away from graduation. I have a diffcult desicion to make about my final year project. I have been offered projects from two companies and one of them is the one i start working for at the...
  9. Z

    Electromagnetic wave /Field question

    Hi i was wondering what's is the difference between electromagnetic waves and fields or is a field just a number of electromagnetic waves. also i was wondering is it possbile to have an electromagnetic wave where there is only a magnetic field and no electric field and vice versa Thanks
  10. Z

    Electric power question

    so if i wanted to measure the total power dissipation for this circuit would be 59W ?
  11. Z

    Electric power question

    Hi if i have a voltage supply of 100V connected across a 66 ohm resistor which has a power rating of 155W. then P=V^2/R=10000/66=151W but say if i had the same situation except i add another resistor in series to increase the resistance of the overall circuit by adding a 100 ohm resistor...
  12. Z

    Voltages across capacitor,inductor for ac voltages

    well i connected a 0.1uH inductor to a signal generator which generated 5V ac voltage and then i added a resistor connected to the inductor and ground. then i measured the voltage across the 10 ohms resistor on a oscilloscope and at was the same as the input so that's why i wondering if i...
  13. Z

    Voltages across capacitor,inductor for ac voltages

    hi i was wondering if we would treat inductors and capacitors as short circuits for AC voltages. i am aware that there is a 90 degrees phase shift in a RC or RL circuit with an ac voltage but the phase shift only applies to the current. thanks
  14. Z

    Where can i buy monochromatic coloured filters(optics):

    hi there i am looking for monochromatic colored filters like on the picture on the following web page: http://en.wikipedia.org/wiki/File:Filter-optics-1.jpg (preferably with no reflectivity) but i have had no luck trying to find them while looking on google
  15. Z

    Choosing the correct type of filter

    hi i bought a machine which determines led colours by measuring intensity for a product. the product has three leds:green,red,orange. the equipment works well for the green and red leds but fails most of the time with the orange leds. i looked up wavelength values for the colours and i...
  16. Z

    PIC programmer advice

    thats super cheap and awesome bassalisk i going to order one after i test the one i am building and colin thanks for the tip i have ordered a 18-pin IC pin socket. do you think it would be safe to put the cct together on a breadboard and connect to my pc via the RS232 female connecter
  17. Z

    PIC programmer advice

    lol i just found this out and it works for the PIC i am working on apparently,its really easy to make and so i am going to attempt to make it check it out: http://www.instructables.com/id/How-to-make-the-worlds-smallest-and-cheapest-PIC-/?&sort=ACTIVE&limit=40&offset=40
  18. Z

    PIC programmer advice

    i have just been reading up on pickit3 programmer but it seems like it you would have to solder the complete circuit together before you program it using the pickit3 by connecting to the pc via usb and you would also need to provide two I/O pins for the pickit3 to connect to the board is this...
  19. Z

    PIC programmer advice

    hello i have been learning about micro-controllers for about a month now and i have started my own private projects using them. at the moment i am using a PIC micro controller for a alarm clock which is programmed in C. I have ordered the parts and designed the pcb but i have had some...
  20. Z

    Pull up resistors

    hi there i have been reading up on the function of pull up resistors from the text:http://ti.tuwien.ac.at/ecs/teaching/courses/mclu/theory-material/Microcontroller.pdf and on page 37 it talks about it. in their example of the pull up resistor with the switch. i was wondering if they circuit...
  21. Z

    Reversed bias diode with applied voltage

    the output end is connected straight into a micro controller model p80C557E (at the interrupt pin) i am not really familiar with micro controllers but should the load be the internal resistance of the microcontroller?
  22. Z

    Reversed bias diode with applied voltage

    yes its drawn in the correct format. it would make sense to me if drawn the other way around
  23. Z

    Reversed bias diode with applied voltage

    hi there i just have a question about diodes say for example we have the following cct: the circuit with the diodes with the 5V supply, one of the diodes is on and the other off and i understand why this happens but when dealing with the circuit the opamp and the diode i am confused. the...
  24. Z

    Fabry perot Laser

    Homework Statement Consider a Fabry-Perot laser, length 0.1m, with an unsaturated gain coefficient, \gammao=1m-1 one of the mirrors of the Fabry-Perot cavity is perfectly reflecting, the other reflects 95% of the light and transmits 5%. wit the aid of a brief calculation explain why steady...
  25. Z

    Two level laser

    Homework Statement consider a two level atomic system , solve the rate equations for the two levels to find expressions for N1(t) and N2(t) in terms of the intial populations N1(0) and N2(0) Homework Equations i have been able to derive the rate equations as...
  26. Z

    Skin depth of a good conductor

    Homework Statement for my assignment given i was told to derive the equation of the skin depth of a good conductor and i derived it as d=sqrt(2/\mu\omega\sigma) then i was told to calculate d where i was given w=10^15 and sigma=10^7 and this gave me a d of d=1.26E-8 which i guess is...
  27. Z

    Pi matching network

    hi i need help with some pi matching for the following cct shown below, i would usually approach this problem with X=sqrt(1000*50) where X is the reactance of L1,C2,C3 but since C1 is in this cct then i can't use this equation so could someone please help me solve this problem
  28. Z

    How to measure the output impedance of this cct

    ugh well if i do it analytically and perform small signal analysis would it be correct to short cct the DC source and short circuit the coupling capacitors and also the capacitor in parallel with the base resistor and inductor. then the output impedance will be completely reactive and given by...
  29. Z

    How to measure the output impedance of this cct

    hi i want to find the output impedance of the following cct so i can perform pi matching on it but i don't know how to find it using lt spice please help! added schematic
  30. Z

    How to bias a transistor into cutoff

    ops i taught i attached it. anway i figured it out, it is used for RF applications
  31. Z

    How to bias a transistor into cutoff

    hi i would like to bias a transistor into cutoff. i have the schematic shown below and for the transistor i am using it has a collector cutoff current at 100nA. so my approach was frist to perform Dc analysis: Vth=5*(R10/(R10+R4)) Rth=(R4*R10)/(R10+R4) so my input equation is...
  32. Z

    Common-collector buffer

    thanks for your help
  33. Z

    Common-collector buffer

    new input and output does this seem correct?
  34. Z

    Common-collector buffer

    DC voltages of base = 3.1V DC voltage of emitter =2.5V
  35. Z

    Common-collector buffer

    omg i can't believe i did not see that. i have now attached the resistors to the base and this the output i get (red/green graph where input is red and output green): i wasnt sure to measure the dc voltage using ltspice so i plotted the base voltage against the emitter voltage (...
  36. Z

    Common-collector buffer

    hi again i tried decreasing the size of the top base resistor but it didnt work so i tried changing the capacitor values and now my output looks like this(output is the green colour). so is the buffer working because in your above statement you said If the output is exactly like the input...
  37. Z

    Common-collector buffer

    sorry i taught i attached it.
  38. Z

    Common-collector buffer

    i have added a capacitor before the transistors base but still nothing is my configuration correct? added schematic
  39. Z

    Common-collector buffer

    i have designed the buffer to have a input impedance of 57.4k, output impedance of 50.9 ohms and gain of 0.99 are those specs good for a buffer and by the way this is the output i get from ltspice
  40. Z

    Common-collector buffer

    hi i am having my frist attempt on designing a common- collector transistor buffer which has a unity gain of 1. i am using lt spice to check the input and output of my buffer, however i am not sure how to determine if my buffer is working. if my input is a square wave with 3 volt amplitude...
  41. Z

    Designing a low-power FM radio transmitter

    hello i have been given six weeks to design a low-power FM radio transmitter for my project however there are no lectures for this course so i have to do the research on my own. so far from researching on the web. i have found that a simple radio transmitter may consist of a number of stages...
  42. Z

    Finding electric field incident on a medium

    \GammaHomework Statement if an electric field is traveling in air and hits a medium n2. then there will be three fields present: the incident electric field the reflected electric field and the transmitted electric field. the electric field in medium 1 would be...
  43. Z

    Half-wave dipole antenna radiation pattern

    thanks for the clear demonstration. so i was wondering if i had a choice between a half wave dipole and a 3 half wave dipole to design. then i should design a 3 half wave dipole antenna because it will have a higher gain ?
  44. Z

    Half-wave dipole antenna radiation pattern

    Homework Statement i just have a few questions about the radiation pattern of a half wave dipole antenna. firstly i know the for the half wave dipole we can dervie and expression for the electric field in the zenith angle and the magnetic field in the azimutal angle by using the far field...
  45. Z

    Finding expression for instantaneous Electric field

    Homework Statement hi i have been given the following electric field phasor E=(z(5)+x(10))e-jpi(y) mV/m Mr=100 er=3 Homework Equations The Attempt at a Solution i have been able to deduce from the results above that wave is traveling in positive y direction. intrinsic...
  46. Z

    Proving stokes theorem

    ok thanks i guess the textbook answers are wrong
  47. Z

    Proving stokes theorem

    Homework Statement for the vector field E=x(xy)-y(x^2 +2y^2) find E.dl along the contour find (nabla)xE along the surface x=0 and x=1 y=0 and y=1 Homework Equations The Attempt at a Solution i tried the second question (nabla)xE over the surface by finding the...
  48. Z

    The discrete fourier transform

    Homework Statement A 8-point data set is transformed with a DFT and the resulting array has values 1,2,3,4,5,6,7,8 was the data set real or complex? why? Homework Equations The Attempt at a Solution kind of confused with this question all i know is the discrete Fourier...
  49. Z

    Finding Aliased Frequencies

    Homework Statement An ADC system samples at frequency of 500Hz. it is preceded by 4-pole low_pass Butterworth filter having a 3db frequency of 1KHZ. Three intefering signals are present at frequencies of 2kHz,2.6kHz and 4.4kHz a) what is the Nyquist frequency of the process? b) what will...
  50. Z

    Error analysis

    yep all cm's
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