SDR - software defined radio

   There has been, for awhile, a device available for computing devices that transcends the usual milieu of printers, scanners and players. The device is a radio dongle.
   A dongle is any device you can hold in your hand and carry in your pocket and plug into one of the USB ports on a laptop or desktop computer. Some cell phones now in use also have usb ports and can use the SDR as well.
The SDR is a programmable radio. At times in the past, different radios had to be purchased to listen to different radio bands. Radios transmit and receive signals on assorted frequencies. There is short wave, military, ham, AM broadcast, FM broadcast, Television, PSK, CW, USB, LSB and many others. All kinds of data in all kinds of formats is transmitted continuously over the radio spectrum.
   The cheapest SDR dongles run around ten dollars. More is better, in this case, meaning spending more can get a better SDR. The quality of reception and range of frequencies increases with cost.
   There is excellent free software to use with the SDR, but familiarity with radio is needed to manage the radio. Basic FM broadcast radio is easy and straight forward. Listening to music or news is easy but will drain the batteries of laptops not plugged in to a wall socket. There is also the NOAA weather forecast made available on radio frequencies specified by NOAA. This elimenates the need for a separate radio for government weather broadcasts. For SDR units with a certain range, cell phone transmissions are detectable. Air traffic signals are available and there is free software to receive the signals, plot the courses on a map and retrieve images and data on the particular aircraft detected. One professor has developed software that uses the SDR as a passive radar device. Another person's software detects and translates tire pressure monitoring sensor activity in passing automobiles. There are also the local community service channels. Police, fire, EMS and 911 are easily scanned once the frequencies are known. The local Wings Air Rescue service is on air occasionally. There is free software to receive transmission from weather satellites in the form of imagery.
   AM radio is usually too low a frequency to detect with an SDR but a hardware add-on called an 'upconverter' makes the task possible.
   Only the lower cell phone GSM band is accessible from an inexpensive SDR. The higher bands and wi-fi signals require a high frequency available in units that typically run a hundred dollars or more. Once the signal is received, the decoding is still needed. When decoding is done, some will require decryption. For this a set of Rainbow tables is generally required. These may require a fast hard drive of several terrabytes (Tb) capacity. Some cell bands are not readily transcribable.
   When all this has been examined and studied, there is the antenna. A good antenna can receive signals from thousands of miles away. However, the antenna shape and size vary with signal frequency and directionality.
   In summing, an SDR can be a convenient way to play favorite radio stations, monitor tor the weather and plot your incoming flight's progress and get the latest news and live local sports.  
   This is all great fun and interesting but anything more sophisticated may require an antenna larger than the pencil sized portable that comes with most inexpensive dongles, and an SDR that is not a dongle but a USB plugin card similar to an external hard drive. The increase in knowledge is proportional.



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