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Field Monitoring

Equipment Required

What is a Discriminator Tap

Frequencies To Monitor

General Guideline

Usually, you're going to use one of the standard ATCS channel pairs listed below. When the railroad isn't using one of the standard ATCS channel pairs, you can find out the specific frequencies to use by importing, within ATCSMon, the appropriate MCP (.mcp or .mdb) files for the target area, then look at the details of the MCPs using the Configure->MCPs screen. If you aren't familiar with importing files, see the Getting Started guides linked at Web Home.

Also available is a database of frequencies known to be in use by various railroads, and the subdivisons. It can be found in the database section of the ATCSMon Yahoo Group: here

ATCS Channels

ChannelMCP (MHz)BCP (MHz)

Frequencies for other protocols

Genisys and SCS128

A 900Mhz capable radio with the discriminator tap is typically required. Union Pacific extensively uses this protocol. They have went through an extensive process with the FCC to license very specific frequency sets for each specific location, and these are not the 6 ATCS channels that have been set aside for ATCS (protocol) use. For the UP, as of this writing (12/2009), my current count for frequency pairs that they use is 36 pairs in the 928/956MHz band and 16 pairs in the 932/941MHz band. I read that this could be as high as 300 sets, but that is not confirmed.

The frequencies typically used, in duplex mode, are in the 928/956MHz and 932/941MHz bands. The lower frequency, in each set, is usually the MCP and the higher freqency is typically the BCP. So if you are monitoring either the MCP or BCP, you can move up or down to locate the reciprocal station (if within radio range).

The Genisys protocol is a 'polled' mode protocol. This means that the BCP periodically, systematically, steps through each possible address and then listens for a response from each one, in turn. So this means you usually hear pretty frequent traffic on the BCP channel, but lesser so on the MCP channel, because of range issues and sheer mass of what polling (talk to each address periodically) does. Also, this means that the address for each MCP is quite short, and not unique to a specific railroad, systemwide. Thankfully, ATCSMon has been setup to provide a unique address based on the zip code of the lowest addressed BCP on a particular district. This is setup in the kits that you can get for each railroad subdivision.

Specific frequencies, and other relevant data, can be found in the database section of the Yahoo Group for ATCSMon: here


A VHF radio with the discriminator tap is typically required. The railroads (BNSF is the only one I'm aware of that uses this procotol) use the standard AAR channels (VHF, typically 160-161MHz) in simplex mode (one frequency for both the BCP and MCP to 'talk' on).

For the BNSF, the following AAR channels are used systemwide:

AAR Ch#07 (160.215)
AAR Ch#17 (160.365)
AAR Ch#25 (160.485)
AAR Ch#39 (160.695)
AAR Ch#40 (160.710)
AAR Ch#41 (160.725)
AAR Ch#47 (160.815)
AAR Ch#57 (160.965)
AAR Ch#60 (161.010)
AAR Ch#81 (161.325)


A UHF (450MHz band capable) radio with the discriminator tap is typically required. Other then the Norfork Southern railroad, all other North American railroads use one pair of frequencies (in duplex mode) for End of Train (EOT) communications. The specific frequency pair is 452.9375/457.9375Mhz. The 452MHz side is the headend of the train (the MARY) and the 457MHz side is the FRED (Flashing Rear End Device) device on the rear coupler of the train.

The Norfork Southern railroad uses an AAR channel for their EOT communication, in simplex mode. The channel is: AAR Ch#67 (161.115MHz)


Equipment required for field monitoring are; laptop with ATCS installed, scanner or data receiver, antenna, cable connecting from discriminator tap to laptop via Griffin iMic.

-- Main.GregMazzie - 14 May 2007 ---

When mointoring both the BCP and MCP channels at the same time, two receivers are required. I use two ICOM PCR-1000's, but any ATCS compatible scanner will do. You actually have to create a "network" for both freqs. to be heard and decoded. One .ini file should be labeled for BCP and one for MCP. In both of these, the display dispatcher layout should be left unchecked. In the options tab, under data source, you would add these two applications to whichever ports you are using. The main application (or combo .ini) will display the dispatcher's layout and will receive the information from both receivers. Anyone needing assistance with this can contact me off-list and I can provide copies of the .ini files that we provided to me by other ATCS users. Its rather simple once you get it set up.

-- Main.GregMazzie - 14 May 2007 ---

-- Main.BrianSwan - 29 Oct 2006