9/6/2019 Rtl-sdr Linux Fm
A subreddit for the low-cost, DIY software defined radio (SDR) community. While originally dedicated just to the project, relevant legal content related to general SDR, RF and similar projects is also welcomed.Feel free to ask questions but please. Rtl-sdr'rtl-sdr' is a generic term for cheap USB digital TV (DVB-T) receivers that use the Realtek RTL2832U chipset, which can function as general purpose software defined radios (receive only). All rtl-sdr compatible devices employ the RTL2832U as an ADC and USB controller, but different RF tuners may be used.Note that rtl-sdrs do not transmit!Typical specs (some depend on specific tuner):. Cost: $5-45 USD. Frequency range: 24 - 1760 MHz (100 KHz - 24 MHz in direct sampling mode). Max sample rate: 3.2 MS/s (2.6 MS/s in practice).
Resolution: 8 bits/sample. Noise figure. The thing I like most is that I can replay past transmissions by clicking in the waterfall history. Using other SDR software, when a new transmission pops up, I feel like I'm in a race to tune to it before it ends so that I can at least hear some of it, but in my software, I don't even have to pay attention to what's happening now, and so I seldom do. Usually I don't notice transmissions on new frequencies until they've ended, but I still get to listen to them.I also put some effort into trying to make sure AM and FM transmissions were equal in volume, as well as at the correct volume according to how well they were modulated, in that I aimed for 100% modulation leading to audio output that's 6 dB below the ceiling. It seemed as if it was quite random in other software, as switching from AM to FM might cause a huge jump or drop in audio volume. I don't like to play with my volume controls, so I did my best to make it so that I don't have to.I'm also not at all fond of the 'click the numbers' method of changing the center frequency which seems to be so common.
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Gqrx receiving broadcast FM using RTL-SDR and Funcube Dongle. Using a newsky dvb-t tuner and a modified version of gqrx that supports rtl sdr. Antenne is a 2m/70cm in my attic. 7 years ago by admin 0. Linux Embedded RTL-SDR Receiver.
So in mine, I just type in the MHz on the number keypad and press enter.I'm also much more fond of my waterfall coloring scheme than any other I've seen. It seems much smoother and more informative, at least to me anyway. I suppose that's rather subjective.but it's rather hard to compare it to other software given that I only got to use other software for two or three days. I rather soon knew I wanted to write my own, and I wanted to use the V4L2 API (that dvbusbrtl28xxu module you have to blacklist to use rtl-sdr is an SDR driver, not a video driver), but I had to upgrade to Linux Mint 18 to get access to it since it's a new API, and after doing so, I haven't been able to get any of the existing SDR software to both compile and work after it's compiled. So I just focused on writing my own, since I was wanting to do so anyway. (No support for that V4L2 API though, as it turns out its buggy and offers no way to control the dongle's gain, so it's basically unusable.). The part I'm not getting is that the descriptions I've seen of how direct sampling mode work make it sound as if they're just connecting the antenna directly to the ADC and so I just process 'I' data rather than 'IQ' data, but the ADC runs only at 2.4 MHz, which doesn't explain how it is then able to tune all the way up to 24 MHz.
So there must be something more to it that hasn't been mentioned in anything I've read.I do see this in rtltcp's source code: case 0x09:printf('set direct sampling%dn', ntohl(cmd.param));rtlsdrsetdirectsampling(dev, ntohl(cmd.param));break;So I guess that's how it's enabled, though what exactly it wants as a parameter remains a mystery. I did find a sort of documentation for rtltcp once, but I forget where it was. I think it was in the source code for some other project.but if anyone with one of these dongles wants to try to figure it out, just open up radio.c and go down to line 909, right after where it says this: void radioinitialize.and after that line add this: sendpacket(0x09, 1).or make that 1 a 2 or a 3 or whatever you think rtltcp might want. That'll make it send the command on start-up and then you can see if that's all it takes to support it or not.If that's all there is to it, I can easily add some buttons to control it.EDIT: While I don't have a dongle that can do this, I did give it a try, and it looks like it works in as much as what I see on the waterfall moves to the left when I increase the center frequency and has a rather bold line where 0 Hz is. So it quite possibly is as simple as sending this packet with some value to enable this mode.However, I'm hitting a brick wall in figuring out what value should be sent.
Clearly zero sets it back to normal mode, and anything non-zero seems to set it to something else, but just how many of the non-zero modes does the user need to be able to choose from, and what should I label them?I having no luck finding the documentation for rtltcp's commands. I should have bookmarked it the first time I found it, but I guess I just left it open in a browser tab for days until I forgot about it.EDIT: After playing with that command a bit, and finally tracking down, I think I've figured out how to make it work. So I put an update on my web site which may or may not support it.
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