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Found 3 results

  1. Hej, I am trying to capture the FM frequencies using HackRF-one. I don't have the regular antenna, so I am using a different antenna (shown below). When I tried to record the FFT plot for the range of frequencies the receiver is able to capture, I obtained a plot as shown in the image below. I am a bit curious as to why the number of peaks and the height (length) of each peak is small. Can it be due to the antenna that I am using or the place where the SDR is operated? I am unable to receive any FM signal from the audio sink. If you have any ideas, please let me know. Sample rate : 20 MHz Channel center freq : 104.3 MHz
  2. Hello everyone, I'm writing my first post in hope of shedding some light on rational resampling in FM radio. My idea was to get started with something easy to get me into the SDR programming and I chose FM radio. I have watched HAK5 SDR episode where the FM radio is built. I have also found similar graph on instructables (links below). I have tried to duplicate their graphs (with my own working frequencies), but without much success. My finished graphs produce loud cracking noise in my headphones. What I noticed, though, is what looks to me a strange discrepancy in the rational resampling and sample rate settings. Now, I'm quite sure I have some basic concept wrong, because it obviously works for both of them. Here's what is strange: 1. Sample rate starts at 2M at RTL-SDR Source 2. It is resampled with interplation 1 and decimation 4, which should produce the sample rate of 500k ("2M * 1/4", if I undestand correctly) 3. Low Pass Filter has also Sample Rate 2M (Shouldn't it be 500k?) 4. WBFM Receive has Quadrature rate of 500k and Decimation 1 5. It is resampled again with Interpolation 48 nad Decimation 500. If we take 2M sample rate from Low Pass Filter, it should produce 2M * (48 / 500) = 192 kHz. But if we take 500k sample rate, it should produce 48kHz, which is also the setting of the audio sink. The problem is, if I put 500k as the Sample Rate of Low Pass Filter, instead of cracking noise I hear only silence. So my understanding is probably very much off. Can anyone shed some light on these problems? Is there another problem present, which is not tied to the GNURadio Companion and resampling? Here are the links: HAK5 episode I watched: Instructables: http://www.instructables.com/id/RTL-SDR-FM-radio-receiver-with-GNU-Radio-Companion/?ALLSTEPS Graph from instructables similar to HAK5's: http://cdn.instructables.com/FFO/PKAD/HNE45JZQ/FFOPKADHNE45JZQ.LARGE.jpg Rational resampling basics I read: http://www.dspguru.com/dsp/faqs/multirate/resampling Any help will be greatly appreciated.
  3. Just for grins and giggles, I compared the speed of processing in software the demodulation that we do in hardware in a traditional radio. There is a small delay, but I am going to guess that it is on the order of 1/10th to 1/20th of a second betwixt the audio coming out of a traditional radio to the output of an SDR setup with a ~$20 or less dongle. For someone who was brought up on 2 Mhz 48K byte computers, this is just freaking amazing. I remember, for the aforementioned specs of the Atari 800, it took every ounce of processing power, including turning off the video chip (about a 20% boost in performance), and everything the poor little thing had to render a 2-3 second clip of the Kinks "You really got me now", and even then, it was a far cry from broadcast or cd quality audio. In retrospect, I should have forecast some of the capabilities of modern computers and modern networks. Realistically, networks have become part of our computer systems. Without a network to stream information from the web or your video server to your ROKU or XBMC pc, the capabilities of our computational power is very limited. The amount of collaboration and innovation that even the community of Hak5 is able to produce through the web site and the weekly I-casts is nothing short of amazing. People from all over the country, or the world, are able to work together, with only language being a barrier, but increasingly, the web is making the world speak English. This trumps every social influence that people or cultures may claim. They may have localized languages, but the web speaks English, and English's place as a world language is all but guaranteed by computer networks, the Internet, specifically. I realise that TCP/IP cares nothing about the human language it transports, but as the innovation in networks and computer science is mainly a product of the US and our economic allies in Japan, Taiwan, China, and the EU, and RFC's ( the backbone of internet/TCP/IP innovation ) are written and distributed in English, I pretty much see English as being the uber-language of the future. My forefathers/mothers spoke German, Norwegian, English ( British English ), etc., but by the fourth or fifth generation, the only thing that matters is old traditional recipes made on the holidays. The rest of the culture has been absorbed. So will it be with our newest immigrants. So it will be with the world as they get absorbed into the world wide web. Many cultures, such as the Japanese and the Chinese and various Jewish and Moslem countries will always preserve their neighbourhood tongues... But they will also speak English, and speaking in English will become the international standard of communication through the influence of Internet Anarchy. If tracked back far enough, the Roman Empire is still alive and well, but wearing different clothes. It is more of something that we all take for granted. Roads ( arguably, an early network, still important in conjunction with the information network ), indoor plumbing ( arguably, an early crap network, sort of like Facebook ), bridges ( ok, more network analogies... ) our calendar and hours, our numerals, all have Roman origins. This is similar to how I perceive English's role in the future, something taken for granted, that people don't even think about. I hope I have not offended anyone. If I have, please accept my semi humble apologies. I don't intentionally try to offend anyone. It seems, like sarcasm, to be a natural talent I possess. -Fuzzy Bunny
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