Quasithermal Noise (QTN)

QTN is generated by thermal fluctuations in the plasma surrounding the antenna. It is most intense at a frequency just above the local electron plasma frequency (fpe), which depends on the electron density (Ne). The electron density, Ne, can be calculated from fpe,

Ne (electrons/cc) = (fpe/9) ^ 2.  where fpe is in kHz

In the Figure, the low frequency edge of QTN is seen at about 10 kHz, until 12:40, then rises to about 20 kHz for the remainder of the day. The abrupt increase of fpe, and therefore electron density Ne results because an interplanetary shock passed the spacecraft at 12:40.