Military Use
Spread-spectrum signals are highly resistant to deliberate jamming, unless the adversary has knowledge of the spreading characteristics. Military radios use cryptographic techniques to generate the channel sequence under the control of a secret Transmission Security Key (TRANSEC) that the sender and receiver share in advance.
By itself, frequency hopping provides only limited protection against eavesdropping and jamming. There is a simple algorithm that effectively discovers the sequence of frequencies. To get around this weakness most modern military frequency hopping radios employ separate encryption devices such as the KY-57. U.S. military radios that use frequency hopping include the JTIDS/MIDS family, HAVE QUICK and SINCGARS.
Read more about this topic: Frequency-hopping Spread Spectrum
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