Applications for Military Radio Retransmission

“Retrans” — short for retransmission, is a common symptom of equipment and technical deficiency that exists among military agencies.

This problem can occur when two or more agencies must work together without sharing encryption keys. It may also occur when an agency needs to extend the range of their own, internal radio communications.

 1. Agencies Using Different Encryption Keys

Soldier with Encrypted Radio Relay

Soldier with Encrypted Radio Relay

 

A real world example of this problem could be, if a U.S. military agency must work with a coalition partner without sharing encryption keys.

 

 

 

During Iron Fist 2014, the 15th Marine Expeditionary Unit deployed the following, low tech solution to the problem of sharing encryption keys:

“that both ends would have American radio operators and American equipment. One American operator would be embedded with the Japanese.”

Article: Marines, JGSDF discover a new way to communicate

2. Long Distance Communications Over LOS Radios

Military units at the brigade level and above may need to retransmit LOS radio communications, in order to integrate forward area personnel into the radio net. Usually, this is a risky operation that puts the retrans team into less secure, more remote areas: Video: Long Road to Retrans

Additionally, these remotely located teams must be re-supplied by convoys, consuming further man-power and resources.

3. Obstructions to RF Due to Rugged  or Mountainous Terrain

Mountain Peak Radio Retransmission Site

Mountain Peak Radio Retransmission Site

RF propagation is highly sensitive to the terrain and structures within its environment. Mountain peaks can block FM radios signals, originating from teams situated on either side of the mountain. A retrans team must be placed atop the mountain to establish a line of sight radio communications link between these teams.

 

This article provides a brief overview of the daunting task of maintaining a radio retrans site atop a fridge mountain peak: Article: Retrans Battle Elements Connect Brigade

An important note: When performing radio retrans, with devices such as the VHF-FM SINCGARS radio….Each time audio passes through a radio, it becomes slightly distorted. When audio is retransmitted through the SINCGARS, it will pass through 4 radios, by the time it reaches the listener. As a result, the speaker may sound distorted to anyone monitoring the retransmitted audio. When speech is digitally encoded and decoded multiple times, it can have a  “robotic” sounding quality.  

Although I discussed the above issues in the context of military operations, public safety first responders may also be familiar with similar communications difficulties.  For example, a figherfighter battling a wildland fire may need to communicate from deep inside a ravine to their remotely located commander, experiencing similar RF environmental challenges, such as those described in 3. Obstructions to RF (i.e. Mountains) Due to Rugged Terrain. 

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