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  1. D

    What's with GSM cell phones and ticking sound into radios, speakers etc?

    GSM uses TDM: time domain modulation. Basically, A GSM phone is allocated many small time slices when it is allowed to transmit. To save battery life, the phone turns off the power amp when it's not transmitting. The switching transients from this are what you hear through your computer...
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    Lenz's Law & Eddy Currents: Questions

    The thickness of the copper pipe (wall thickness, not pipe diameter) will affect the speed. Thicker copper means lower resistance, which causes the eddy currents to be more effective at slowing the magnet. The easiest way to show this effect is to get a larger diameter pipe that fits over the...
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    Looking for grad schools

    I'm an EE grad at UCLA. The big names here are in RF and analog IC design. I don't know any good power programs off the top of my head, but I would advise you to search the last couple years of ISSCC and JSSCC for Class D amps, DC-DC converters, etc to see what schools are publishing work in...
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    What causes alkaline batteries to leak?

    Mixing old and new batteries can cause the old ones to leak. Also could be due to overheating (e.g. leaving your maglite in the car on a hot day).
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    Should I use the Arithmetic or Geometric Mean?

    I'm fairly confident that when refering to means, the terms 'aithmetic' and 'geometric' are used in the same sense as they are when refering to sequences.
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    Building an electromagnetic gun of some sort

    I recently saw a very cool science science project that might qualify. Hold short (~4 feet) length of copper pipe vertically and drop a neodymium magnet through the center. Anyone here care to guess what will happen?
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    Inductance of a coplanar waveguide

    For something free, check out AppCAD (made by Agilent, the same company that makes the MUCH more powerful ADS). It's great for calculating Zo of various transmission line structures. Once you have Zo you can back calculate inductance using Zo = sqrt(L/C) and c=1/sqrt(LC), where L and C are...
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    RF transistors

    RF transistors are usually junction devices (BJTs or HBTs), not FETs. These transistors are better suited to building high speed amplifiers and other RF blocks due to a number of factors, including: more transconductance for a given bias current, better matching, and higher speed operation...
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    IC EDA tools

    Hmm... I use cadence IC design tools at school and they don't crash that often, but they do crash. If you're seeing lots of crashes it might have something to do with the system setup. I agree the GUIs are definately craptastic though. From what I here many designers in industry don't even...
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    How do smaller die sizes allow for better performance?

    1.6nm gate oxide THICKNESS, not gate length. I'm doing analog design so the clock rates aren't that high (~300MHz).
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    How do smaller die sizes allow for better performance?

    Not that far off, actually. Gate oxide thickness is 1.6nm for the 90nm process I'm working in.
  12. D

    .

    There's no reason an iterative filter shouldn't work just fine. I do not agree that a moving average (FIR filter) will be more accurate than an iterave one (IIR filter). You can design a good low pass filter with either one, but an IIR will use fastly fewer resources and introduce much less...
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    .

    A low-pass filter may work for your application, but it is NOT giving you a true mean, just a local mean. That said, I don't know why you would want a true mean, because after a sufficiently long time the mean will basically not respond at all to new input. With a LPF you can track the input.
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    Can some explain the difference between Digtal and Analog Circuits?

    Analog circuits operate on analog signals, which are real physical quantities such as voltage or current. Digital circuits operate on digital signals, which are abstractions of real physical quantities (i.e. 0-0.5V = "0", 0.5-1.0V = "1"). Digital circuits are great as long as you are only...
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    What exactly is light? And why is "the speed of light" considered to be fastest anything can move?

    to move at the speed of light a particle must have zero mass, or it would take infinite energy to accelerate it. photons meet this crtiterea. i'm not aware of anything else that does.
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    Faraday Cage calculations

    wavelength = (speed of light)/frequency
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    Faraday Cage calculations

    I would assume that the holes need to be significantly smaller than the wavelength. 1 GHz wavelength is about a foot in free space, so holes of a few inches should be small enough.
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    How effective are COTS RF amplifiers?

    Yeah, that should do it. Keep in mind that if you do use a filter you might also have to use an amp to overcome the filter loss.
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    How effective are COTS RF amplifiers?

    It might help. You are correct that an amp will amplify noise already on the line, but the tuner card contributes its own noise and amplifying the signal will reduce its impact. Generally you only need an amp if you are splitting the signal many times. If you don't see any improvement by...
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    The DIY robotics thread.

    Cheesehead: What C compiler are you planning to use? I did some work with a PIC a couple years ago and at that time the compilers were so expensive (and I was getting paid so little) that I ended doing it in ASM.
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    I guess this is technical

    Triangles ABC and EBD are similar (same angles) so their sides will have the same proportions. So, DE/BE = AC/AB and DE = (AC*BE)/AB = 3.5*42/162 = 0.91
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    Complex Fourier transforms and Quadrature detection

    Yes, mixing preserves phase. Why wouldn't it? Many wireless communications standards use phase-only modulation because a constant amplitude signal allows the use of a much more efficient power amplifier. If mixing didn't preserve phase then none of these radios would work.
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    Complex Fourier transforms and Quadrature detection

    What do you mean by an 'f - fr' signal? You mean just multiply the original signal x(t) by cos(2*pi*fr*t)? If you did that, then becasue of aliasing you would end up converting both 100 - 101 MHz and 99 - 100 MHz to DC - 1 MHz, corrupting your signal if there happens to be another channel at...
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    Power Supply Depepdence of 741 Op-amp

    Puma, the CB amp you keep reffering to is only a common mode loop. I'll reffer to the schematic here: http://www.uoguelph.ca/~antoon/gadgets/741/741.html Q11, Q12, and R5 set the main bias current to Ibias = (Vcc+Vee-2*0.7)/39k, which is directly dependent on supply voltage. This is mirrored...
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    Power Supply Depepdence of 741 Op-amp

    In general, open loop opamp gain is a poorly controlled (and relatively unimportant) parameter, so I'm not supprised is varries so much with supply voltage. This is definately coming from supply-dependent bias currents. The circuit used to gererate the bias reference is a 39k resistor in...
  26. D

    Help Defining a Wave

    I would say that the defining characteristic of a wave is it's periodicity. A wave is some phenomenom we identify that, as you said, exists in a medium, and posesses a measurable quantity that is periodic or quasi-periodic in either space or time or both. Something that has nonzero frequency.
  27. D

    Canon SD 200 Dig Camera $169.88 w/free ship

    I got in on this a few days ago for the girlfriend's xmas gift. Great point-and-shoot camera. IMO, the higher resolution of the SD400 or SD500 isn't worth the extra $100-$200 if you're only printing standard photo size. I've got a 3MP and I never see pixelation in my prints.
  28. D

    Recommend a FPGA

    I've never used them, but I've heard the Xilinx Spartan series is a good low cost FPGA. You can get 1M gate parts for ~$80 or 1.5M gate parts for ~$120 through www.digi-key.com. Looks like Xilinx has some free development software called ISE WebPACK, just don't expect it to be convienient to...
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    Digital Sampling

    Uhh, NO. Absolutely not. How are you going to sample at every moment in time? And why would you want to? As long as your sample rate is greater than twice the highest frequency component in the analog signal, you lose NO information from sampling. Loss of information happens as a result of...
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    Looking for the best digital camera deal on black friday

    I'm in a similar situation. Been looking at the Canon SD200, which is $180 w/ free shipping from Amazon.
  31. D

    Leaving an AC charger plugged in

    Mark: It was my understanding that EVERY AC-DC converter needs a transformer for isolation. A power supply connected directly to the mains would be extremely dangerous, wouldn't it?
  32. D

    IBM Cell as GPU

    I understand that GPUs are mostly just DSP and can be developed quickly using logic sythesis tools (Synopsis, etc). And Cell is general purpose DSP, so it will be slower than something designed for a specific purpose. But I don't think it should be THAT much slower. I acknowledge that there...
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    IBM Cell as GPU

    I'm not that farmiliar with the hardware that's inside a GPU (I'm an analog guy). I guess I just want to know if Cell's SPEs could mimic that hardware well. Isn't that what a GPU does? Lot's of fast math in parallel? Thanks for the comments everybody.
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    IBM Cell as GPU

    Before I get flamed as a Linux freak let me say that the open-source thing was just an afterthought. What I'm really interested in is the techical feasibility of a Cell-based graphics card.
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    IBM Cell as GPU

    I'm sure everyone here has heard of IBM's Cell processor (aka the PS3 processor) and its highly parallel architecture, but here's Anand's latest take on it just in case: http://www.anandtech.com/cpuchipsets/showdoc.aspx?i=2379 It sure seems like the Cell would make a decent GPU. It's got...
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    IBM Cell as GPU

    I'm moving this to the Video forum as it's probablly a better fit there.
  37. D

    IBM Cell as GPU

    I'm sure everyone here has heard of IBM's Cell processor (aka the PS3 processor) and its highly parallel architecture, but here's Anand's latest take on it just in case: http://www.anandtech.com/cpuchipsets/showdoc.aspx?i=2379 It sure seems like the Cell would make a decent GPU. It's got...
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    Difficult Probability question for any math wizzes out there!

    While this does give a low number, it's not THAT low. But there are some very large numbers involved and if you try to do it on a calculator you might overflow a register and get garbage results. If you write out N1 above most of the terms drop out and you get: N1 = 30!/[(2^6)*(6^6)] N1*p...
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    Difficult Probability question for any math wizzes out there!

    I'll take a shot at it, although it's been a little while since I did any combinatorics so go easy on me... Let N =the number of ways to split people up into 12 groups that satisfy the constraints p = the probability of a particular combination = (1/12)^30 then the probability of meeting...
  40. D

    Probability Question for Y'All...

    Yes, this is one of the differences of a bernoulli distribution from a normal distribution. So obviously (n+k) must be even.
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