# Search results

1. ### RF Signals - Radio waves or electrical signals?

Hi all Sorry if this is quite a basic concept, but I am confused about RF signals. The way I currently understand it is that radio waves in space are an oscillating electric and magnetic field at 90 degrees to each other traveling through a medium. However, when you pass a radio wave into a...
2. ### Matched filter vs. Incoherent detection

I am having trouble seeing how a matched filter for FSK is any more "coherent" in its detection than an envelope detection incoherent FSK demodulator. The matched filter simply requires a precise sampling time at the output, however, surely so does the incoherent FSK demodulator? Matched...
3. ### Power Spectrum vs. Power Spectral Density Spectrum

Thanks for the reply. Ok, that's fine, but now I have a question about obtaining the PSD of a signal that is continuous in the frequency domain. I have read it is simply the square of the magnitude of the spectrum. If we assume that the spectrum was obtained with the Fourier Transform, surely...
4. ### Power Spectrum vs. Power Spectral Density Spectrum

Does anyone know the difference between the power spectrum of a signal and the power spectral density (PSD) spectrum of a signal? I've read on the net lots of things ranging from: i) They are identical ii) Power spectrum is units of Watts, power spectral density spectrum units of Watts/Hz...
5. ### LTI Difference Equation from Impulse response

Sorry for the delayed reply. I think I understand what your saying - instead of using two IIR filters and subtracting their outputs (one delayed), you can use one IIR filter and subtract it's inputs. I can't do a block diagram because I don't have any webspace to host the image at the...
6. ### LTI Difference Equation from Impulse response

Thanks for the reply. I think I understand the jist of what your saying. I'm not sure but would h[n]_{iir} be: h[n]_{iir}= x[n] + h[n-1] In which case would: h[n]= x[n] + h[n-1]-x[n-N] - h[n-N] be correct?
7. ### LTI Difference Equation from Impulse response

Sorry for the confusion, I should have written it in a clearer form with all the conditions. The h[n] = {1, 1/2, 1/4, ...} for n>=0 was wrong. There should not have been a "..." at the end. The example, even in the hard copy of the notes, specifically states: h[n] = (\frac{1}{2})^n for...
8. ### LTI Difference Equation from Impulse response

Hi rbj The first h[n] is the correct one i.e. (FIR). Sorry if this caused any confusion. Thanks! Paul
9. ### LTI Difference Equation from Impulse response

Hi rbj Thanks for your replies. I don't have much experience in DSP (as you can probably tell). 1) Perhaps I should give more context. I was just trying to relate two concepts from my lecture notes and they may or may not be indirectly linked to truncated IIR filters. I wanted to...
10. ### LTI Difference Equation from Impulse response

I've been told that to calculate the difference equation of an LTI system, you simply take the sample values of the impulse response as the coefficients of the x[n-k] terms in the difference equation. i.e. if h[n] = {1, 0.5, 0.25, 0.125} for n>=0, then y[n] = x[n]...
11. ### Spectrum of 6V 15W Tungsten Microscope Lamp

Dear All I am trying to measure the spectrum of an incandesant 6V 15W tungsten microscope lamp. I have a reasonably old scanning monochromator (diffraction grating based) coupled to a fibre optic cable and it has given me the spectrum below...
12. ### DSB-AM Modulation Index for Multitone Signals

Homework Statement A carrier wave has an rms voltage of 10V. It is modulated by a signal having compenents of frequencies f1 and f2 and the rms voltage of the modulated carrier rises to 11.5V. If the modulation index due to one of the components is 60%, calculate the modulation index for...
13. ### Schottky Barrier Band Diagrams

Dear All I am having problems with how to draw band diagrams with band bending for Schottky Barriers and PN junctions. My issue is that I don't know how you determine which Fermi level remains fixed at its equilibrium level and which Fermi level moves to align with it when the two materials...
14. ### Skin depth

Dear all I am slightly confused over the equations for skin depth. My university notes give me the equations: \delta = tan-1 (tan\delta) = \frac{\sigma}{\omega \epsilon} (loss tangent) where \delta is skin depth and \sigma is conductivity. I am also given the equation: \delta =...
15. ### Second order pole positions and rise time

Thanks for the reply viscousflow :) I see what your saying for the most part. But surely for a fixed imaginary part (+/- jwd) moving the poles left would decrease the angle and cause dampening to INCREASE since it's cosine ? Thanks Paul
16. ### Second order pole positions and rise time

Dear All I'm stuck on something that seems to be contradictory. I was under the impression that the further the 2 closed loop poles are in a 2nd order system to the left of the root locus, the higher the damping. Surely high damping means longer rise time? But other sources say that the...
17. ### Calculating Unit Impulse Response

Hi Klondike Thanks for the reply. Glad I'm on the right track :) We've been chucked in at the deep end with no prior experience in SP of any kind and just a load of notes with definitions and no explanation! There was a previous exam question like this yet no examples on how to do it...
18. ### Digital vs. Analogue Signal Definition

Thanks for the reply. Just to clarify, a signal can be considered digital if it's continuous in time but discrete in voltage? Also I guess I should have explained, I meant after the sample and hold part of the ADC but before the actual conversion takes place. Thanks! Paul
19. ### Digital vs. Analogue Signal Definition

Dear all I am slightly confused over the definitions of digital and analogue signals. Is a digital signal discrete in time AND voltage or just discrete in voltage. For example, could a square wave that is continuous in time, but has discrete voltage levels be considered a digital signal...
20. ### Calculating Unit Impulse Response

I am trying to teach myself DSP, owing to bad lecture notes. In particular at the moment I'm trying to calculate impulse responses for LTI systems, given the system equation. I would really appreciate it if someone could tell me if my working and assumptions below are correct for the following...
21. ### Capacitor and inductor problem

In the analogy, the mass does accelerate as I said in my last post (dv/dt is large) since the pushing force and the reaction force are on different bodies. For the example of the stick, whilst there is a reaction force on the stick, this does not cancel the fact that that the stick is applying...
22. ### Capacitor and inductor problem

Thanks for the reply gneill. I understand that analogy; There is a large dv/dt for the mass since the two forces are acting on different objects (NIII law pair). However, I don't see how that analogy can be applied here since surely both the capacitor's emf and the inductor's "back emf" (which...
23. ### Capacitor and inductor problem

Thanks for the reply collinsmark. You have definitely clarified my issue with the first problem. I was thinking that short circuiting the inductor would suddenly decrease the current in the inductor for some reason, whereas it actually would remain constant. I still have some issues...
24. ### Capacitor and inductor problem

Dear All I am struggling with 2 different problems with the basic concept of inductance and capacitance. 1) Firstly, I am not sure if I am understanding correctly how (hypothetically) an initially "charged" inductor can sustain, when short circuited, a constant current. I am right in...
25. ### Mealy State Machine Design

Once again thanks for everyone's replies. They've all been really helpful! Shame I wasn't good enough to think the same way as fillip and do it with 4 states from the start but I got there in the end :) I realize my diagram is quite messy but the bottom half of the state table does show that...
26. ### Mealy State Machine Design

Hi everyone Thanks for your inputs. I think I have managed to do it with 4 states (an initial state being included within another state). I did it by simplifying my initial 9 state model by drawing out the state table and realising quite a few states were identical. I've attached the...
27. ### Mealy State Machine Design

I will post the state table up soon as the diagram I have draw is VERY messy what with all the transitions between the 9 states and labelling! Can anyone else do it in 4 and an initial state? Thanks Paul
28. ### Mealy State Machine Design

Thanks for the replies! I have managed to get a working state machine with 8 states plus and initial like phrak said. However, I am concerned this is not the most efficient way of doing it if Filips 5 state way works. Filip, would it be possible to explain or scan in and attach your...
29. ### Mealy State Machine Design

Electronics: Mealy State Machine Design I'm having trouble with designing the Mealy state machine below: Homework Statement A state machine is to have two inputs X and Y and an output Z. The output should stay at a constant value unless one of the input sequences occurs below: a)...
30. ### Ball twirling on string attached to stick

No, for small angles cos(theta) is approximately 1. Therefore your formula becomes Mg=m(w^2)R. That's your proof since this formula is the same as for the original case with no "dipping" of the tennis ball.

Dear All I am having trouble understanding the gradient vector of a scalar field (grad). I understand that you can have a 2D/3D space with each point within that space having a scalar value, determined by a scalar function, creating a scalar field. The grad vector is supposed to point in...
32. ### 2.4GHz radio signal through small gaps

Thanks for the reply. I need a material that is non-toxic in case the resin were to break open. Whilst I am sure a pebble breaking here and there and exposing a tiny bit of lead carbonate would pose little if any environmental damage/toxicity, there would still likely be a restriction on its...
33. ### 2.4GHz radio signal through small gaps

For an engineering project I am trying to place a 2.4GHz RFID tag inside a resin casting of a large seaside pebble. However since the resin is less dense than a real pebble, I need to add some mass of metal (since is is much denser) to the resin before it sets. It is crucial for the casting to...
34. ### Shock detection switches

Thanks for reply. I could attempt to cut one open but I would prefer not to since I only have a week left to write the report and may need to test all of them. I can't find any patent filed by Assemtech or a patent on any similar device. I have found something that suggests it could be a...
35. ### Shock detection switches

As part of an engineering design project, I am using shock switches to measure accelerations of an object. As the name suggests they are just switches that turn on when a shock above a certain value is experienced. Does anyone know the details about how the switch contact is closed when it...
36. ### Positive and negative electrical terminals

Thanks for the reply. Does this mean that the negative / positive terminals of the battery are barely higher/lower in potential than ground. Otherwise surely just connecting the negative end of the battery to ground would cause current to flow? Also, why does connecting the positive...
37. ### Positive and negative electrical terminals

I am slightly confused as to why some circuits are drawn with a positive input terminal and a negative input terminal, whilst others are just drawn with a positive terminal and a ground (OV) terminal. What is the difference between ground and negative? Does negative indicate an excess of...
38. ### Find all the accelerations of the 3 masses and the 1kg pulley

Dear All I have a question about tension in a mass system with pulleys. The question asks you to find all the accelerations of the 3 masses and the 1kg pulley. It also asks you to find the tensions in the ropes. I have used d'Alembert's principle to do this and appear to have the...
39. ### Thermodynamics water/water vapor question

I am having problems with a Thermodynamics question: I am struggling to work out why the meniscus would move up at all. Surely its maximum height is the height of the meniscus at the very beginning when all of the water is liquid? Once the water is added, some evaporates as the...
40. ### Dynamics/Mechanics problem

I am assuming that it means uniform tangential acceleration, since that it the direction of the velocity increase. Surely this means that the side force cannot be constant at 6800N, rather it is an upper bound, since radial acceleration HAS to increase?
41. ### Dynamics/Mechanics problem

Thanks for the reply. So, presumably, I need to work out the angular acceleration (alpha) for w(0) and w(t). Do I do this by using the vector sum of the accelerations, substituting in w(0) and w(t) and rearranging for alpha?: 11.33^2=((w^2r)^2)+((alpha*r)^2) If I do this for w(0) I get...
42. ### Dynamics/Mechanics problem

Sorry but I still do not understand. Since the resultant force ( side force of 6800N) is constant and the tangential force is constant (uniform acceleration), surely the radial force has to be constant? But it isn't since w is increasing.
43. ### Dynamics/Mechanics problem

Thanks for reply. I believe that what the question means by side force is the overall resultant force acting on the side of the car from the radial and tangential forces combined. Hence the the magnitude of the total "resultant" force on the car is the side force of 6800N. So this force and...
44. ### Dynamics/Mechanics problem

I am attempting to solve the dynamics question below: "A car of mass 600kg is driven in a circle of constant radius (100m). It is known that the car becomes unstable under a side force of 6800N. Determine the minimum time allowable for the car to accelerate uniformly from 80 to 100km/h."...
45. ### Friction on an inclined plane

I am having problems with a simple problem with a mass (m) stationary on an inclined plane of angle θ. I have obtained the equations for the reaction/normal force and the force acting on the mass parallel to the plane: Reaction force / normal force (R) = mgcosθ Parallel force = mgsinθ...
46. ### Thing called an inertia force

Thanks for the link. I think that has made it a bit easier to understand. Thanks for all your help. Paul
47. ### Thing called an inertia force

Thanks for your reply. I am finding it really hard to get my head around the reference frames. Please could you explain the reference frames and the forces present in each a bit more and also why it is that you feel that you are pushed into your seat if there is only one "real" force...
48. ### Thing called an inertia force

I was told today in a lecture that there is such a thing called an inertia force that occurs only when an object is accelerated by a force. I was also told it is equal in magnitude and opposite in direction to the force accelerating the object. Obviously you can feel this in a car - when you...
49. ### Calculating driving force from wheel rpm, wheel radius and engine power

Thanks for your replies guys. I suppose I should have stated that I need to eliminate torque from the equation. This is because the force needs to be calculated from a Power vs. engine rpm curve. I have no direct information on the engine torque so it needs to be calculated from the power...
50. ### Calculating driving force from wheel rpm, wheel radius and engine power

I have spent a while trying to work out a simple equation to give me the driving force of the engine in a car using the inputs: Power, wheel radius and rpm but when I put in real numbers from a production car, I get low values of 2197N. The equation I have derived is: Driving force =...