Although the term may seem intuitive, there are many ways to interfere with radio signals. Generally speaking, jamming is the deliberate blocking or interference of radio signals. For decades, totalitarian regimes such as Russia and China have used wireless signal jammers to jam signals from other countries or transmitters that send messages they don't like. Signal jamming has a long military history, including jamming communications, jamming drones, and jamming GPS.
If we tune the transmitter (HackRF in this case) to the same frequency and modulation type, and have enough power, we can “drown out” the signal coming into the receiver. Some of the most common types of interference include sending random noise, random pulses, staircase tones, pulses, and sweeps.
The main limitation we have to focus on is signal strength. These only work when we are close to the receiver or can project a very strong signal. In addition, the Russian military signal jammer uses frequency hopping technology, the signal changes frequency at a very fast rate. In this case, we might use multiple transceivers and target multiple frequencies (we don't need to target all frequencies as the missing components would interfere with the signal sufficiently) or set the transmit bandwidth very wide to cover multiple frequencies.
Signal jamming has a long and storied history in military tactics. Although some military communications are encrypted (many Russian shortwave communications are unencrypted and can be intercepted), that doesn't stop us from jamming them. Essentially, jamming it prevents the signal from being picked up like a receiver. This could have important military implications.
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