![]() ![]() I’d also like to see it pushed up the frequency band (5.8GHz) if possible, just to get away from most interference. I’d love to see an RF front end board made, as $250+ of connectorized parts is out of my budget, but students in a class are not expected to have MMIC waveguide design experience, either. More research still ahead.Īs for the presentation, I did enjoy it, it cleared up a few points I had questions on, but it was more like an end of class “this is what I learned” presentation, not something that extended the knowledge of his professor. I’m not exactly convinced that he needed an integrator, either, on the front end. I’d have to look into noise floors and ENOB at frequency. I can’t say I agree with either Drone or rsdio on the A/D conversion. Are they actually doing any quadrature on this? I thought it was all based upon frequency analysis via FFT and rejecting the Q component (I peeked at the Matlab files). I’m not certain IQ would help in FMCW, most notes I find apply that to pulse doppler. It’s about as simple as you can get, which was the point. The entire front end was designed by the professor for the summer course. ![]() Of note, I am an interested hobbyist, not an RF engineer nor an ARRL RF guru. I’ve been reading and researching this design over the last few weeks, got some thoughts for you, Drone. Sometimes, other DAC technologies are way more suited for non-audio purposes. ![]() 192 kHz might be fast enough, but 24-bit audio DAC chips have plenty of noise shaping, where it’s fairly cheap to get a DAC that is less than 24-bit but avoids the sigma-delta modulation that creates all that noise. A 44.1 kHz ramp would have serious stepping, and those steps would cause FM problems. I think that the speaker did a good job of explaining that the 250 kHz sample rate is needed to generate a smooth ramp. A 250 kHz A/D is also cheaper than you might think, and it can be a precision part that is vastly better than an audio A/D. But radar processing probably isn’t going to be too happy with that same noise when it comes to imaging from faint signals. Cheap 24/192 sound cards are great for audio, because the 8 bits of quantization noise that they have can be easily ignored by the human hearing system. Now, where did I put my There are more differences between a 24/192 audio A/D and a purpose-built 250 kHz A/D than you seem to be allowing for. If I were the Author’s Adviser at MIT I’d be doing a bit of advising about this. The use of foul language in these public presentations is insulting not only to the audience (me), but to the character of the speaker. Why build a complex 250kHz data acquisition system? Truly excellent yet affordable high dynamic range 24-bit 192kHz sound cards are available today (even as USB dongles) – and they’re stereo, so accepting quadrature input is a no-brainer.Ĥ. All are relatively inexpensive COTS parts (), and with a little more design effort, they can also be built for next to nothing as microstrip elements directly on the PCB (decent quality FR4 board will work fairly well at 2.4GHz, see for the mixer diodes.).ģ. The demodulated bandwidth of interest is relatively small compared to the carrier frequency, so quadrature dividers would be used to split the local oscillators, then image reject mixers would be employed for down conversion. Hardware quadrature demodulation is preferential for RF down conversion (over digtal delay quadrature) and is cheap and easy to accomplish in this application. Why is there no IQ (quadrature) demodulation? In applications like this quadrature demodulation simplifies almost all DSP tasks. Also, it is not until the very end that a Doppler related question from the audience evokes the mentioning of up-down chirps.įor a brief explanation of chirps in radar see the section on “Frequency Modulation” here:Ģ. Early-on in the presentation, the important concept of chirp in CW-FM radar is not explained well at all. ![]()
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