The Noxon DAB USB stick I got as a cheap ... / 2012-03-20

2012-03-20 The Noxon DAB USB stick I got as a cheap ... 7 years ago
The Noxon DAB USB stick I got as a cheap DAB/DAB+ experimenting device has hidden powers. A big part of the 'cheap' is because this device leaves all of the work to software. If I understand the discussions about the Noxon correctly, there are drivers to receive dvb-t signals with the same stick. Most development for the linux driver seems to be on the dvb-t side too.

I came across a webpage which puts this all in a new light: The whole device turns out to be a wideband tuner and an analog to digital convertor. Software has to do the rest. And now someone has written that software. Some clever thinking and discussion started by Antti Palosaari turned into rtl-sdr, a software defined radio using the RTL2832U chip. Together with my other thoughts about software defined radio where I thought about receiving and decoding D-STAR ham radio signals with for example a funcube dongle this means I already have a software defined radio. Time to capture some I/Q data and learn about gnuradio. The rtl-sdr software has already been used to receive Tetra signals (frequencies UHF 380 MHz .. 476 MHz) and GMR signals (satellite phone, L-band 1600 MHz). So I guess 70cm D-STAR should not be a problem.

Update 2012-03-21:
Spectrum of 3M broadcast band
Simple FFT (spectrum analysis) of data coming from the NOXON dab usb stick. Works in the VHF FM broadcast band, I can see various signals and verify their frequencies. With stronger stations I can use the wideband FM decoder in gnuradio and get audio. Click for full screen capture from gnuradio FFT.
Played with this, and I managed to receive an FM radio station and decode the stereo audio from it using the grc (gnuradio companion) rtl2832 to fm scripts mentioned here. Hearing a bit of radio received and decoded by hardware which absolutely wasn't sold to me with that capability is fun. Everything gnuradio is all new to me so most of the time I have no idea what I'm looking at and the noise in the Noxon stick is causing issues as usual.

Update 2012-03-22: Played some more, and added the plot. And I heard audio from some of the stronger stations. But I still have serious noise issues, even when moving the usb stick away from the computer with a long usb extension cable. As you can see in the plot there is not much difference between the noise level and a strong local station. The wideband FM receiver module available in gnuradio companion couldn't even decode the signal at 93.8 MHz (Slam!FM Noordbrabant) in the captured data.

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