Tuesday, June 12, 2018

An Ideal Soundtrack My Amtrak Adventure

Last week, as I was sitting in the Amtrak waiting area at Union Station, it occurred to me that I could try tuning in to the behind the scenes operations. I did a quick Google search for Amtrak radio frequencies and this page came up. I plugged my SDR dongle into my Linux laptop and kicked off this rtl_fm command:

  rtl_fm -f 160440000 -l 20| \
   tee ~/dl/chatter.raw |  \
   play -t raw -r 24k  -es -b 16 -c 1 -V1 -

Along with a burst of static, I could clearly hear radio traffic! I quickly ran through squelch values, and found that -l 200 kept the static at bay. Here's a sample of what I heard:

The relative calm of the waiting area contrasted nicely with the near continuous discussion over the radio.

It seems that whenever I get inspired to listen in on radio traffic, I spend nearly all my time trying to dial in the right frequency; usually giving up before I hear anything. But not this time, everything just worked!

Pulling away from the station, I found that the traffic ceased. As we approached other stations, I tried to tune in again. rtl_fm supports monitoring multiple frequencies at once, making for a command line radio scanner. Here's a command line I used to listen in on multiple Amtrak channels:

 rtl_fm -f 160.425M -f 160.650M -l 200 | tee ~/dl/chatter.raw | \
   play -t raw -r 24k  -es -b 16 -c 1 -V1 

And here's a command line that scans nearly all 100 of the known Amtrak channels:

rtl_fm -l 200 \
-f 159.81M -f 159.93M -f 160.05M -f 160.185M -f 160.2M -f 160.215M -f 160.23M \
-f 160.245M -f 160.26M -f 160.275M -f 160.29M -f 160.305M -f 160.32M -f 160.335M \
-f 160.35M -f 160.365M -f 160.38M -f 160.395M -f 160.41M -f 160.425M -f 160.44M \
-f 160.455M -f 160.47M -f 160.485M -f 160.5M -f 160.515M -f 160.53M -f 160.545M \
-f 160.56M -f 160.575M -f 160.59M -f 160.605M -f 160.62M -f 160.635M -f 160.65M \
-f 160.665M -f 160.68M -f 160.695M -f 160.71M -f 160.725M -f 160.74M -f 160.755M \
-f 160.77M -f 160.785M -f 160.8M -f 160.815M -f 160.83M -f 160.845M -f 160.86M \
-f 160.875M -f 160.89M -f 160.905M -f 160.92M -f 160.935M -f 160.95M -f 160.965M \
-f 160.98M -f 160.995M -f 161.01M -f 161.025M -f 161.04M -f 161.055M -f 161.07M \
-f 161.085M -f 161.1M -f 161.115M -f 161.13M -f 161.145M -f 161.16M -f 161.175M \
-f 161.19M -f 161.205M -f 161.22M -f 161.235M -f 161.25M -f 161.265M -f 161.28M \
-f 161.295M -f 161.31M -f 161.325M -f 161.34M -f 161.355M -f 161.37M -f 161.385M \
-f 161.4M -f 161.415M -f 161.43M -f 161.445M -f 161.46M -f 161.475M -f 161.49M \
-f 161.505M -f 161.52M -f 161.535M -f 161.55M -f 161.565M | tee ~/dl/chatter.raw | \
   play -t raw -r 24k  -es -b 16 -c 1 -V1 

Though, I have no idea how practical a list of frequencies this long is.

There's something empowering about listening to behind the scenes radio traffic. It's like glimpsing a secret world while your fellow waiting-room dwellers are none the wiser. I don't ride Amtrak frequently, but next time I do I'll arrive ready to tune in.

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