A software-defined radio system, is a radio system where components are implemented in software instead of special hardware. A recent post in the slashdot about an implementation of this system using very cheap DVB-T/DAB receivers. Following up the links, i discovered the reason behind this: the RTL2832U chip. Searching a bit more i got a list of supported hardware. Searching in local shops i bought a Lifeview LV5T Deluxe usb receiver and i started to play (~20 euro).
First of all, i had to install a different usb driver from the default. After that you have to download and install the HDSDR program. Finally, you have to install a plugin at the top of HDSDR to control the receiver. First experiences seems promising: receiving local radios and local tv stations. The HDSDR application supports FM demodulation, so i was able to hear (with some modifications in the sample rate etc) local radio. Unfortunately, the receiver does not support lower frequency band less than 64 MHz. Moreover, the quality of the software demodulation was low, and the sound includes a great amount of noise, although you can understand the conversations. I 'm not sure about the source of the low quality results, but i had to play with the sample rate of the us device (for the radio i used 0.90001 MS/s with 96000 output sample rate) and for exploring the frequency band over 300MHz, 3.1MS/s.
Here is an example screenshot running the HDSDR and searching the band around 88 MHz:
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| HDSDR receiving 86.4 MHz. Note that the signal is an artifact as explained in comments. |
The 86.4 MHz signal is an artifact. You will note that if you remove the antenna, all radio stations get weaker, but the signal at 86.4 MHz will stay. It's the third harmonic of the main clock of that rtl device, which is provided by an 28.8 MHz crystal
ReplyDeleteMichael are you sure ? I know that there is an artifact in 87.6 MHz, in the center and it's more obvious i higher frequencies. I will give a try today, although i 'm far away from the location i took the screenshot.
ReplyDeleteI am sure that the RTL2832U dongles are mostly clocked at 28.8MHz (the other clocking option is 36MHz). I am also sure that my Trekstor-branded DVB/DAB/FM stick with a FC0012 tuner does get an artifact at 86.4MHz which is a super stable unmodulated ultra-sharp peak in the spectrum. I can get that line without connecting any kind of antenna.
ReplyDeleteI rechecked your picture, too, and your 86.4MHz line looks by far not that sharp as the line I observed, which is a couple of Hz wide, at most. So you might likely have a real signal at that frequency.
Michael, yes i confirm, this is artifact of the RTL2832U. I 'm currently north of Toronto and i have the same line. However in the uploaded picture the line is not sharp like what i'm wathcing now. So it is possible that there was some external source, but for sure there is an artifact.
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