EW Academy · Contents · Chapter 24 · §24.3 · Nederlandse versie

§24.3 COMJAM: the aim and the J/S contest

Open §24.3 in the academy

In plain terms

To disrupt a conversation you do not have to shout louder than the speaker — only louder than the speaker at the listener's ear.

In practice

A drone jammer therefore only has to overpower the receiver in the drone, not the pilot's powerful ground station. A small jammer close to the target, on a vehicle or in a trench, often works better than a large jammer far away.

The aim of COMJAM is not "making noise" but degrading command & control (C2): if the opponent cannot communicate reliably, he cannot coordinate, adjust or synchronise his fires. The effects are classified as deny, degrade, disrupt and — at the boundary with cyber — deceive (CEMA: cyber & EW).

As with radar (burn-through, Burn-through and the J/S ratio), COMJAM is a contest at the receiver. The jammer competes with the transmitter for the attention of the receiving radio; what decides it is the J/S ratio at that receiver. The crucial consequence: you do not have to overpower the powerful transmitter — it is enough to saturate the receiver. A jammer close to the receiver therefore has an enormous advantage.

transmitter (theirs) receiver (target) signal (long path, weak) jammer jamming (short path, strong)
COMJAM geometry: the jammer only has to beat the receiver, not the transmitter. Close to the receiver, a modest jammer wins against a distant, powerful transmitter — hence the value of stand-in and drone-borne jammers (Counter-UAS & drone EW).

The bar is raised the smarter the target link is: the processing gain of spread spectrum (Spread spectrum, hoppers and mesh networks) greatly increases the required J/S. A robust, coded digital link needs far more jamming power than analogue voice.