Troposcatter and SATCOM Communications

Recently a story appeared in Nextgov that looked at the Army’s use of tropospheric scatter (troposcatter) communications, a technology that dates back to the Vietnam conflict. The article seemed to suggest that in many scenarios troposcatter systems can be a replacement for SATCOM connectivity delivered to VSAT terminals.

I served as an Operations Officer for a Marine Communications Battalion in Iraq. I managed several TRC-170 troposcatter systems in Camp Fallujah and in Al Asad. This method of communications uses the tropospheric scatter phenomenon, where radio signals are transmitted in a tight beam aimed at a point in the sky midway between the transmitter and receiver. The signals scatter as they pass through the troposphere, allowing the receiver station to pick up the signal

The technology has some uses, but troposcatter systems cannot replace VSAT for the preponderance of communications in theater.

There are several reasons why TRC-170 troposcatter systems are difficult to use: size and mobility of the equipment, power requirements, training of operators and maintainers, and setup time. A TRC-170 troposcatter system is generally moved by a large vehicle pulling a trailer carrying the required parabolic dishes for transmitting and receiving signals.

The system has its own separate generator for power. Personnel with separate occupational specialties are required to operate and maintain the system.  Finally, the setup time for a TRC-170 far exceeds that of most VSATs. It usually takes a crew of four several hours to set up a TRC-170.

As you can see, it requires a great deal of effort to set up and use a troposcatter radio system.   The DoD is now asking industry to look at taking the TRC 170 and shrinking it to the size of a man-pack radio. Instead I would suggest focusing effort on currently fielded satellite systems and making those systems more cost effective by investing and implementing advances in modulation and encoding/decoding.

Some of the performance and cost metrics cited in the Nextgov piece are also a bit incomplete.  For example, a price of $500,000 is mentioned for a current TRC-170 system. This is accurate, but leaves out the support, maintenance and operations costs.  Once these costs are added in to the initial cost of only the TRC-170, then the overall cost of ownership exponentially rises.  It’s like talking about the ownership cost of a vehicle, without counting fuel, spare parts, maintenance, trained operators and maintenance repair technicians, etc.

Similarly, I never experienced a throughput of 12Mbps using troposcatter in the field. True performance in ideal conditions was closer to 8Mbps.

I told a former colleague who is still an active duty communications officer in the Marine Corps about the Nextgov article, and this is what he said:

“TRC’s work well if you are in a safe environment, not too mobile and have the supplies needed to operate and maintain the system (fuel and spares). You also need the appropriate terrain without a hill or another unit in front of your antennas.”

Troposcatter systems can be effective tools for the largest, most secure forward operating bases. In almost every other scenario, VSAT provides and protects the ISR advantage our troops require in the field.

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