Due to its vast territory, Russia is one of the biggest users of HF radio for military purposes.

Analog voice networks

Several stations (Buzzer, Pip, Air Horn...) use a channel marker transmitting a simple characteristic sound continuously 24/7 on their respective frequencies. The waveforms of these channel markers are believed to be generated with simple analog electronic circuits based on transistors, astable multivibrators and the like. As such, they are sensitive to small variations of the analog characteristic values of the circuit or of the supply voltage (caused as simply as turning on another device on the same circuit), which often result in variations in pitch, pace and such of the marker sound that are noticeable on the air. Likewise, these signal generators are not perfectly reliable and occasionally fail, sometimes turning off with a characteristic "dying" sound evocative of discharging capacitors, then leaving the channel silent until the problem is fixed. The channel markers are switched off the air before the station sends a message, and switched back on afterwards.

Several of these stations are on the same network: messages can be heard successively relayed on different stations a few minutes apart, and for example the channel marker sound of the Pip can be heard faintly in the background during Squeaky Wheel messages.

Morse code networks

Proprietary modems

Supplementary resources

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