5 ms·

Feel free to ask any questions about the rtl-sdr project. I've been watching it since it started and have since gotten a handful of commits into the project.

by keenerd 14y ago

Feel free to ask any questions about the rtl-sdr project. I've been watching it since it started and have since gotten a handful of commits into the project. Some key things that were not mentioned. There is the GQRX frontend and the SDR# frontend. Both are fairly straightforward to set up and use. Also not mentioned were the hardware differences (r820t vs e4000 vs fc0013). To get decent signals you need to add a bit of filtering to the USB power supply. And of course antennas, but that topic needs an entire book. I've been working on a very simple sdr stack (currently merged in rtlsdr as rtl_fm) that is meant to provide a sox-like experience. It is also stupidly fast, enough so that even a little RaspberryPi can easily do pager decoding or police scanning.

yuvadam 14y ago
I'd love to read more on USB filtering. Could you point me to any resources?
- keenerd 14y ago
  Ferrite clips/donuts are recommended and easy to install. Put capacitors in parallel with the power, exact values vary. If you are feeling really ambitions, add ferrites in series with the power lines or give the dongle a solid metal enclosure. The simplest is using a usb extension cable, the computer itself generates large amounts of broadband noise. http://electronics.stackexchange.com/questions/25951/ http://electronics.stackexchange.com/questions/25951/ http://electronics.stackexchange.com/questions/36040/ http://electronics.stackexchange.com/questions/36040/
femto 14y ago
Over what frequency range can the dongle be tuned? What is its useful bandwidth, and is it limited by the radio/sampler or the USB interface? Also, what sort of sensitivity/noise figure do you get? Any comments on inter-modulation performance? Lots of questions, but I'm curious as to how these receivers compare to a more traditional rig, and where the limits of performance lie.
- keenerd 14y ago
  The tuning range depends on the hardware. See the first table at http://sdr.osmocom.org/trac/wiki/rtl-sdr http://sdr.osmocom.org/trac/wiki/rtl-sdr for details. All have 2.8MHz bandwidth. A (relatively) simple hardware mod lets you bypass the tuner and pick up 0Hz to 28MHz. Noise and sensitivity vary. I know at least one person ran a bunch of tests with a spectrum analyzer. (Can't find that link though.) Performance generally seems to be limited by the poor shielding/filtering and the low quality timing crystal. If you fix the worst flaws, they are rather capable. For example, they've been used for GPS and radio astronomy. Biggest differences with a more traditional setup is the lack of a transmitter and the questionable build quality.

by keenerd 14y ago

yuvadam 14y ago

I'd love to read more on USB filtering. Could you point me to any resources?

keenerd 14y ago
Ferrite clips/donuts are recommended and easy to install. Put capacitors in parallel with the power, exact values vary. If you are feeling really ambitions, add ferrites in series with the power lines or give the dongle a solid metal enclosure. The simplest is using a usb extension cable, the computer itself generates large amounts of broadband noise. http://electronics.stackexchange.com/questions/25951/ http://electronics.stackexchange.com/questions/25951/ http://electronics.stackexchange.com/questions/36040/ http://electronics.stackexchange.com/questions/36040/

femto 14y ago

Over what frequency range can the dongle be tuned? What is its useful bandwidth, and is it limited by the radio/sampler or the USB interface? Also, what sort of sensitivity/noise figure do you get? Any comments on inter-modulation performance? Lots of questions, but I'm curious as to how these receivers compare to a more traditional rig, and where the limits of performance lie.

keenerd 14y ago
The tuning range depends on the hardware. See the first table at http://sdr.osmocom.org/trac/wiki/rtl-sdr http://sdr.osmocom.org/trac/wiki/rtl-sdr for details. All have 2.8MHz bandwidth. A (relatively) simple hardware mod lets you bypass the tuner and pick up 0Hz to 28MHz. Noise and sensitivity vary. I know at least one person ran a bunch of tests with a spectrum analyzer. (Can't find that link though.) Performance generally seems to be limited by the poor shielding/filtering and the low quality timing crystal. If you fix the worst flaws, they are rather capable. For example, they've been used for GPS and radio astronomy. Biggest differences with a more traditional setup is the lack of a transmitter and the questionable build quality.