Interview: Wireless Bay Area Adventure with USRP B200 Software Defined Radio
By Erik Luther | Thursday, September 12, 2013
Inspired by the capabilities of the new USRP B200 Software Defined Radio, our own Balint Seeber – Ettus Research Applications Engineer by day and SDR wizard by night, set out to show what the new USRP is capable of with a broad frequency coverage from 70 MHz – 6 GHz, a bandwidth of 56 MHz, and entirely USB 3.0 bus powered, board-only design. We didn't see Balint for a week after we handed him the B200 device. I did have the chance to interview him when he got back.
Here's his story:
Luther: What inspired your signal scavenger hunt with the USRP B200?
Seeber: Two and a half years ago I was lugging batteries up the side of the hill in Sydney, Australia to power my first USRP1. Now I can take the USRP B200 and my laptop anywhere unbound by the shackles of wall power. With this newfound freedom I was ready to explore San Francisco's radio spectrum!
Luther: Where did you go on this wireless adventure?
Seeber: I was thinking about the postcard-style photos you see of San Francisco and all of the great RF signals you might find in those locations. I ended up climbing mountains in the middle of the night, tracking ships in the early morning from above the Golden Gate Bridge, locating airplanes from hill tops near the airport, and listening to FM and TV signals from the center of the Bay. I even created a Google Map of my trek.
Interactive Google Map of the Route
Luther: What motivated your first stop near Moffett Airfield?
Seeber: The USRP B200 has a lot of bandwidth and I intended to exercise it, so my first stop was a Primary Surveillance RADAR near Moffett Airfield that was rumored to be visible from the road. Overall, I was curious how the USRP B200 performed with strong wideband signals and was interested in determining the type of RADAR system. Using the USRP B200 and my laptop I performed a frequency sweep in HDSDR and found its transmission in the upper 2 GHz band. Curiously, the RADAR pulses were different from what I've seen in the past. With a little research I discovered that the signals I was seeing were from a RADAR running in Dual PRF (Pulse Repetition Frequency) mode, which is actually used for simultaneous weather observation and aircraft approach tracking. It took a couple trips to the site, but ultimately I was able to analyze the pulse parameters in real time.
Luther: How did you end up climbing a drainage ditch on San Bruno Mountain and crack your cell phone screen?
Seeber: I was looking for a high vantage point to record Mode S Secondary RADAR so that I could plot real-time plane location information. I ended up on the side of the San Bruno Mountain wearing four layers of clothing to fight the strong winds and blistering cold. From there I was able to see planes take off and land at San Francisco Airport and create a live map their flight paths. The unfortunate part was when I lost my footing: I saved the USRP, but my cell phone wasn't so lucky!
Airplane flight path mapped using Mode S
Luther: The photos over the Golden Gate Bridge are impressive. What did you find there?
Seeber: The view from Battery Spencer Park was breathtaking. From that vantage point I could see the entire city and ships around San Francisco. Pulling out my laptop and USRP, I ran an open-source AIS decoder and maritime mapping application (openCPN) to show the location of both ships I could see and others further off in the distance. After scanning the spectrum and finding trunked radio networks and public safety channels, I decided to relax a bit and listen to FM radio coming from Sutro Tower with a GNU Radio application that also decodes RDS station information and local traffic conditions.
Live AIS Boat Traffic from Battery Spencer Park
Luther: Did visiting Sutro Tower allow you to capture signals you couldn't from above the bridge?
Seeber: Actually, I wanted to check out the USRP B200 performance with HAM and ISM band signals in the presence of strong out-of-band signals. What better place than beneath Sutro Tower, a perch for San Francisco's many powerful radio and digital TV transmitters? Some SDR's really struggle with out-of-band signals and I was pleased that the B200 performed well. I was able to track the locations of Bay Area HAMs transmitting their positions over APRS, see FLEX pager messages being sent, and watch the bursty wireless traffic of the 900 MHz ISM band.
Luther: Where was your final stop in this week long adventure?
Seeber: I found a new-and-improved airport overlook in a cul-de-sac on the side of a hill. Although it was night time, I managed to capture some nice footage of parallel landings and takeoffs, and record video of the very same planes being mapped in real time on my laptop. This brought back memories of my nights in Sydney where my friend and I camped out on a hill with a USRP1 near the local Airport following air traffic and experimenting with the Mode S decoder.
Two Airplanes landing at night at SFO with real-time position plotted on the map
Luther: Did anything unexpected happen on the journey? I heard something about police!?
Seeber: At one point I did manage to slip and fall, breaking my B200 in the process but at least I caught my laptop. Also on that last neighborhood stop a resident must have told the police that a crazy Australian with binoculars and a video camera was spying on them. However it was all cleared up amicably when local law enforcement stopped by: the police officer seemed to be entertained by my "airplane research".
The moment Balint Seeber realized the B200 was broken
Luther: So what's next in your adventures with Software Defined Radio?
Seeber: MIMO for sure. I've been using the USRP B200, but the USRP B210 features two channels of coherent MIMO. I haven't done any MIMO implementation before, so I look forward to diving into the field and creating some compelling GNU Radio demos that use this MIMO capability of the USRP B210.
USRP B210 (2x2 MIMO, 70 MHz – 6 GHz)
Luther: Alright, last question. Where could someone get all of these great examples if they wanted to go on their own B200 adventure?
Seeber: Once you have a B200 and a computer, the rest is easy. I would start on GNURadio.org and CGRAN.org. There you can find tutorials and examples, respectively, which cover a broad range of applications (many of which can be set up easily using PyBOMBs). Also I use free apps, such as HDSDR, for spectrum scanning and listening to new signals.
Open source software development toolkit that provides signal processing blocks to implement software radios.
Open source repository for 3rd party GNU Radio applications
GNU Radio install management system for resolving dependencies
Freeware interactive spectrum analysis and radio listening
Open source concise chart plotter and navigation software, for use underway or as a planning tool.
Luther: Thanks for sharing your adventures and documenting them so well with photos and video. We look forward to the next one!
Seeber: My pleasure. I was thinking the radio spectrum in Hawaii needs exploring if you'd let me have a go at it for another week.
The interview: Balint Seeber (Left), Erik Luther (Right)
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