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About the TriMet scanner

Listen to most every call heard on the TriMet radio system

After multiple years, the TriMet scanner underwent an upgrade on 4/28/2021, both the Web page and the call recording program.

It now uses 3 RTL-SDRs, low-cost USB Realtek software-defined radios originally meant for European digital broadcast TV reception. 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. Trunk Recorder is able to take that raw signal and decode multiple channels from it at the same time.

The Council Crest and Mount Scott radio towers of TriMet's radio system are now being monitored. This increases the amount of bus calls that are being recorded, however some may still get missed as calls to buses are only heard on the radio site that the bus is connected to at the time.

Columns are as follows:

The "Fewer columns" check box hides some of the less important ones.

Rows with red-colored text indicate that the emergency bit is set (this has been seen after MAX signal trips). This background color is set when rows are selected to play; this background color is set when rows auto-play.

The same instance of Trunk Recorder is now also being used to record calls on Oregon State Radio Project system's Portland Central Simulcast and send them to OpenMHz and Broadcastify.

Before 4/28, only the Council Crest site was monitored. However, some bus calls on the Mount Scott site were recorded on a different computer (using DSDPlus) and transferred. In addition, from 3/12/2021-4/28/2021, Portland Streetcar calls on the City of Portland's radio system were also being recorded this way; it was decided to discontinue doing so instead of attempting to integrate them into the new version. They can still be heard on OpenMHz where Portland's system is being recorded by others.

I have a list of radios seen and bus radio events (calls, affiliations, etc) are being logged and are viewable on a map (using the same vehicle location data that my SystemMapper app uses).

The HTML is based on:
HTML5 Audio and Video and how to make a playlist
HTML5 Audio Playlist
HTML audio tag
Live version:
Google Maps util.js
Javascript - Append HTML to container element without innerHTML

Code available on GitHub at rosecitytransit/trunk-recorder:newtrimetscanner

decoding rate chart

2017 recordings per day 2018 recordings per day 2019 recordings per day 2019 recordings currently present 2020 recordings per day


By Jason McHuff, rctmail@jasonmchuff.net