Also known as: scrambling, whitening

Scrambling (whitening) XORs data with a public pseudo-random sequence to break up long runs of identical bits, which helps clock recovery and keeps the spectrum balanced.¹ It is not encryption.

Scrambling (whitening) XORs data with a pseudo-random sequence to avoid long runs of identical bits.

How it works

Both ends know the same sequence, so the receiver de-scrambles by XORing again. This guarantees frequent transitions for timing and avoids a DC bias, regardless of the data.

Relevance to SDR

Recognising that whitening is reversible (unlike RC4 encryption) explains why a scrambled-but-unencrypted signal still decodes.

Sources

1. Scrambler — Wikipedia, for XOR-with-pseudo-random whitening to balance the spectrum and aid clock recovery. ↩

See also

• Clock recovery
• RC4 (ARC4) cipher
• Forward error correction (FEC)
• Demodulation

Learn it step by step

• The demodulation pipeline