Technical details

Notice: old system info

Please note: this is describing the original (2011-2014) system which monitored the analog SmartNet-based city of Santa Clara radio system. The SVRCS system beta went live in 2014 and is using slightly different hardware and software, but the basic princples apply.


The original Super Trunking Scanner production backend used a USRP1 with a DBSRX2 daughterboard for radio reception. This photo shows that unit with some extra antennas installed for another daughterboard.

This is all running on a normal (but beefy) Linux box. A fair amount of CPU power is required to keep up with the decoding work.


The backend was a custom project built on top of GNU Radio to decode the control channel and drive audio logging handlers. It took the raw I/Q data arriving from the USRP (about 115 Mbps, 24 hours a day) and saved it to separate calls.

The frontend is a combination of HTML, CSS and Javascript which creates a web application in your browser. It uses AJAX for seamless updates.

Why this matters

Unlike ordinary scanners, this system receives all channels simultaneously and can record all of them in parallel if necessary. Even if multiple talkgroups are active -- police and fire, for example -- you'll still hear every call.

Would you like to know more?

The development of this project was documented in a series of web log posts. Start here for the details.

Just take me to the calls!

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