How Rangecast Works


For most applications, the ultimate source of audio is a fleet of scanner radios.

A "scanner" is a specialized radio receiver that monitors communications broadcast over the public airwaves. Various entities (both public safety agencies and corporate organizations) are licensed to utilize radio spectrum for two-way communications, and when voice transmissions are "in the clear" (not encrypted) they can be monitored by any member of the public with commonly available radio receiver equipment. In some cases, this capacity is an important feature for the broadcasting organization; for example, many volunteer fire departments depend upon volunteers in the public being able to monitor their communications through consumer-grade radio equipment. And it is widely understood that news media access to certain public safety communications is beneficial for the dissemination of accurate information.

Although scanners are very useful, they have their limitations:

  • A scanner can "scan" for new communications on channels operated by multiple agencies, but it can only "listen" to one communication at at time. Therefore, whenever two agencies broadcast simultaneously, the listener is certain to miss content.
  • A scanner must be positioned so that it has good reception of the desired signals, which precludes use in some situations. For example, locations inside an office building may have poor signal, or signals may be poorly received due to interference from other radio transmitters such as cellphone broadcast towers, and of course it's not possible to receive signals at all from communities that are too distant.
  • Since scanners are physical radios with speakers, a scanner can only be used by people who are physically near enough to the receiver to hear the communications. Although scanners are available as consumer products, they are still moderately expensive (typically $500) so many organizations don't want to give scanners to every employee who could benefit from access to the communications. But if employees can't hear the scanner radio, because it's too far away, it's not useful.

  • Rangecast solves all of these problems, and makes it economical to deploy scanners in a way that ensures everyone in your organization never misses important content.

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    At receive sites, scanner radios are attached to a PC. The connection interface (called RCX) carries both audio and data, and is for several purposes:

  • The PC receives audio from the scanner, so the audio may be distributed via Rangecast
  • The PC monitors what broadcast channel the scanner is receiving, so that the audio of every individual transmission can be associated with a specific originating broadcast channel
  • The PC can administer a signal survey, using the scanner to evaluate the quality of reception conditions
  • The PC can reprogram the scanner, so the selection of broadcast channels being monitored may be updated

    A single PC can support multiple scanners. It is customary to deploy up to 4 scanners with each PC (the limiting factor is the performance of the Windows real-time audio processing system, and we know of PCs supporting up to 6 scanners.) If more scanners are desired at a location, multiple PCs can be used (this is also beneficial for redundancy, in case a technical problem takes a specific PC offline.)

    Multisync requires that all PCs supporting any scanner in a cooperative group (that is, all the scanners scanning the same broadcast channels) operate on the same LAN, so the PCs can communicate directly with each other while managing the cooperative tuning of the scanners. (This is not done via Internet to reduce latency.)

    Co-located scanners are usually assigned the same programming (list of channels to scan.) But sometimes it is advantageous to use different antennas or bandpass filters to optimize reception of particular signals, and in this case the scanners may be assigned to different "clusters" each with their own programming.


    All recorded audio is uploaded to an "audio library" located in the cloud (Amazon S3.) All played audio is retrieved from this library (not directly from the receive site PC or originating scanner.)

    Rangecast receive site PCs can operate behind a firewall that blocks all inbound connections. With Rangecast, there are no inbound network connections to a receive site PC. (A common assumption is that the Rangecast HTML5 player must make a network connection to the PC where the audio is being captured, so the PC must be configured to accept network connections, but this is not true.) The only outbound connections needed are to standard ports (80 and 443) at our domain ( and Amazon S3 (, meaning that Rangecast will work on a receive site PC if it has normal Internet access sufficient for using a web browser from that PC.


    Voice to Text: Automated Listener Alert Service (ALAS)

    Rangecast can process audio through a voice to text engine, as a premium service. If this option is selected, automated alerts (SMS or e-mail) will be sent if our keyword detection algorithm indicates a significant possibility of certain words or phrases being present in the spoken audio. In addition, a rough transcription is made available in the Rangecast player, and it is possible to do keyword searches within the player.