Permanently activates the built-in preamplifier on Rigol RSA3000 series real-time spectrum analysers. A preamplifier reduces the DANL (displayed average noise level) giving better visibility of signals close to the noise floor. Each licence contains a unique product key. The product key is used to generate a software licence code that must be entered into your instrument. To generate a Rigol software licence code using your Rigol product key, please see HERE. Installed software licence codes are permanent – They are unaffected by Rigol firmware updates.