It uses RTL-SDRs, low-cost USB Realtek software-defined radios originally meant for European digital broadcast TV reception, specifically 2 NooElec NESDR SMArt receivers. Unlike regular radios which can only capture one frequency at a time, these devices are able to see 2-3 MHz of spectrum and pass all of it to a computer program for processing.
The Trunk Recorder program is able to take that raw signal and decode multiple channels from it at the same time.
The King County Metro Transit Trunking System uses APCO P25 Phase II trunking (Wikipedia, RadioReference) and Trunk Recorder was one of the first programs to understand the protocol.
Columns are as follows:
This site was created by and is maintained from afar by Jason McHuff of
rosecitytransit.org and @rosecitytransit. The HTML is based on:
HTML5 Audio and Video and how to make a playlist
HTML5 Audio Playlist
HTML audio tag
Google Maps util.js
Code available on GitHub at rosecitytransit/trunk-recorder:kcmscanner
None of this is in any way affiliated with or endorsed by King County.
From 8/4/2019-2/24/2021, there was a channel for Link Light Rail, Transit Police and other groups that use the Seattle-King County Public Safety (KCERS) radio system. This audio comes from a PSR-400 radio scanner which is scanning all of the transit-related channels on the system and, unfortunately, it is not possible to save which one is currently active.
As of July 2020, those with a Radio Reference/Brodcastify account can also listen to these channels there:
(Police: Tactical, Sound Transit Security, Transit Tunnel Security 2, Transit Tunnel Security 1 are not publicly available on Broadcastify)
In addition, both the King County Metro Transit and Seattle-King County Public Safety (KCERS) systems are now available on OpenMHz.
View of the radio spectrum in the area of the King County Metro Transit Trunking System as seen by