Portability was important because I needed to carry my entire setup to and from my apartment building’s roof, where my particular location in an outer borough of the city provided more advantages. Must use an FM signal, pick a heavy-metal station “since heavy metal is closer to white noise.”) The second reason is that pointing a directional antenna away from the reference source means that it’s less likely to be swamped by the reference signal. First, while the KrakenSDR can work with many signals including FM radio or cell-tower transmissions, digital TV signals are best to work with because they are fairly evenly distributed across the channel’s broadcast band, unlike the narrower and more variable signals from an FM station. The radio’s manufacturer, KrakenRF, recommends directional Yagi TV antennas for two reasons. The next step was to get suitable antennas. Normally,Īn amateur looking to do direction finding would have to wave around a directional antenna, something difficult to do while, for example, driving a car.īut it was the KrakenSDR’s ability to do passive radar that really caught my eye as a new capability in lowish-cost radio tech, so I plonked down the money. What that means is that, for example, you can arrange five omnidirectional antennas in a circle, and do radio direction finding by looking at when a transmission arrives at each antenna. The Pi is connected to the SDR via a data link, and in turn the SDR is connected via coaxial cables to two directional TV antennas. It’s receive only, but it boasts not one or two tuners, but five! The tuners are based on the RTL R820T2/R860 chip, and they are combined with hardware that can automatically do coherence synchronization among them.īoth the KrakenRF SDR and the Raspberry Pi 4 require a fair amount of power via USB C cables, so a battery pack is needed for mobile operation. I was researching diving back into SDR with one of these devices when I spotted the CrowdSupply campaign for the US $399 Some of these new SDRs can transmit as well as receive, such as the HackRF One or Lime Mini. This includes RTLx-based USB sticks built with better supporting components and designs versus the original TV tuners, and completely new receivers such as the RSPDx. Building off the demand stimulated by this activity, a number of manufacturers have started making premium, but still relatively cheap, SDRs. An explosion of interest in SDRs followed. The biggest leap forward happened in 2012 when it was discovered that USB stick TV tuners using the RTL2832U demodulator chip could be tapped to make very cheap but effective SDR receivers. IEEE Spectrum since 2006, when SDR became something remotely within a maker’s budget. I’ve checked in with amateur SDR developments for I was interested in passive radar because I wanted to put a new software-defined radio (SDR) through its paces. Frequency shifts indicate the object’s speed via the Doppler effect. If a reflection from an object is detected, then the time it took to arrive at the surveillance antenna gives a range. The reference and surveillance signals are compared. A reference antenna picks up a signal from, say, a cell tower, while a surveillance antenna is tuned to the same frequency. Passive radar doesn’t send out pulses of its own and watch for reflections. But for once, I realized I could use this kaleidoscope of electromagnetism to my advantage-with a passive radar station. Radio interference plagues the metropolis. If we could see and hear radio waves, it would make an EDM rave feel like a sensory deprivation tank. Normally, when it comes to radio-related projects, my home of New York City is a terrible place to be.
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