This week Claire said we could post about whatever we liked, I don’t know if it’s supposed to relate to research so I’m going to post about RTL-SDR’s & SDR’s in general as I think they’re awesome!

This is what a typical RTL-SDR looks like.

To explain what an RTL-SDR is I will start with the SDR part of the acronym, SDR stands for Software Defined Radio. The term Software Defined Radio is reasonably modern and the original term used is explained best by the Wiki entry “The term “digital receiver” was coined in 1970 by a researcher at a DoD laboratory. A laboratory called the Gold Room at TRW in California created a software baseband analysis tool called Midas, which had its operation defined in software”  Then “The term “software radio” was coined in 1984 by a team at the Garland, Texas Division of E-Systems Inc. (now Raytheon) to refer to a digital baseband receiver”.
In basic terms a software defined radio takes the components of a radio that have historically been hardware e.g. Mixers, Modulators, Demodulators etc & emulates them using a computer.

This is what a classic SDR setup looks like with a desktop computer out to the right side of frame.

RTL-SDR’s are a specific type of SDR that can be created by putting custom firmware on a standard DVB-T stick that has a Realtek 2832U tuner (Hence the RTL in the name). The reason for the excitement is that the SDR’s available before the RTL-SDR technique was discovered by two guys named Antti Palosaari & Eric Fry, were all extremely expensive and could cost hundreds or thousands or more, a DVB-T tuner with a Realtek 2832U costs around $20.
The RTL-SDR can demodulate frequencies from around 22MHz – 1700MHz which means you can listen to FM radio, Marine Radio, Certain Ham radio frequencies, Tracking Aircraft from their ADSB transceivers, Tracking boats  AIS transponders, Scanning for Cordless Phones, Sniffing GSM signals, Receiving & decoding GPS signals, Receiving NOAA Weather Satellite images, Listening to the ISS, Radio astronomy, Tracking weather balloons, Listening to Police/Fire/Ambulance, Decoding Pager messages, Spectrum Analysis, Triangulating the source of a signal to name just a few of the possibilities of the RTL-SDR.
The only real disadvantage of the RTL-SDR compared to the more expensive SDR’s is that it can only demodulate and has no way of modulating a signal so you can’t do some of the more advanced things SDR’s are capable of e.g. Intercepting wireless car keys or Changing the text on digital highway noticeboards.
This brings me to the end of this post & a picture of the SDR I brought from China last year, which can do a lot more than a RTL-SDR, it’s called a HackRF One.

A HackRF One


The HackRF One is a half-duplex SDR transceiver meaning it can transmit & receive, but not simultaneously. It can also operate at any frequency from 1MHz – 6GHz, a huge increase in range compared to the RTL-SDR. This means it can listen and transmit within the 2.4GHz unlicensed bandwidth, which is an interesting frequency range due to all the technologies that use it e.g. WiFi, Bluetooth, Smart Meters etc.





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