The Harrisburg Chapter of the NRHS maintains a network of ATCS receivers and internet servers covering much of the NS Harrisburg Division. This system allows railroad enthusiasts to view train locations, switch and signal settings and train routing on a graphical display in much the same way as a railroad dispatcher. Using a freeware (no cost) program called “ATCS Monitor” users log into the Harrisburg NRHS’s router to receive the data in much the same way as one would receive railroad radio transmissions via an Internet scanner feed.

What is ATCS?
ATCS is the Advanced Train Control System and is a form of 'radio code line' now being used by the railroads. Previously, signal, switch and track indications and controls were done by way of the wayside copper wires. Later, railroads began using fiber optic cables for this purpose. However, there have been on-going reliability issues. Copper and fiber on poles is subject to wind, ice, lightning and other weather effects. Underground it’s subject to lightning, washouts and back hoes. (Yes, lightning is still a problem underground)! One failure in one location could affect a dozen or more interlockings. To deal with this, ATCS radio code line was developed. By using digital UHF radio, ATCS eliminates the physical connectivity that hampered the signaling systems in the past.

How is ATCS Useful to Railroad Enthusiasts?
ATCS radio signals are NOT encrypted which makes them fair game for anyone with the right equipment to receive. Everyone asks the question, “Is this legal?” The answer is a definite YES! Just as there is no prohibition against receiving railroad voice communications, there is also no prohibition against receiving railroad ATCS signals. As a result, technically oriented railroad buffs formed yet another off-shoot of our hobby: ATCS monitoring. If you have the right type of receiver and freeware software (written by Dave Houy), you can receive the ATCS radio signals and display the information on a computer screen in much the same way as it would appear on a railroad dispatcher's display.

The biggest limitation to receiving ATCS radio signals is that they are in the 900 MHz region. This makes them nearly line-of-sight. The signals are easily blocked by hills, buildings and even heavy vegetation. The railroads solve this problem by placing their equipment on high mountains and/or tall towers. Their high locations give them a clear, line-of-sight 'view' in all directions for many, many miles. Most railfans don't have that advantage. As a result, the typical railfan only has ATCS radio reception for a few miles of railroad in any direction.

Railfans work around this problem by pooling their resources and tying their receivers together by way of the internet. The railroads have one site that covers many, many interlockings. Railroad buffs have many sites, each of which only covers only a few interlockings. However, when you combine the reception of a bunch of railfan sites together, you can begin to cover an entire rail line almost as effectively as the railroad's mountain-top location.

Why the Harrisburg NRHS Became Involved
At Harris Tower, we wanted an exhibit that would replicate what the dispatchers see on their computer screens. The display would allow visitors at Harris to contrast how the railroad was controlled by Harris Tower in 1943 vs. how the railroad is controlled today. To make this display work we use ATCS signals to display a facsimile of the NS Harrisburg Terminal Dispatcher’s computer console. The exhibit contains two, wide screen monitors that display the entire territory of the NS Harrisburg Terminal Dispatcher (the territory that includes Harris Tower). Along with the computer displays is a radio receiver tuned to the Harrisburg Terminal Dispatcher's voice radio. The image below shows a screen capture of the computer display.