Reception at Dunedin of the magnetospheric signal at 6.6 kHz transmitted from Anchorage, Alaska, showed both linear and nonlinear amplification during an event lasting some 20 min near local midnight. Linear amplification of the transmitter signal was ∼20 dB. Natural whistlers were also amplified but often at frequencies sharply limited to those from the transmitter frequency upward. Nonlinear amplification (NLA) produced a signal positively offset from the transmitter frequency by 20–150 Hz at amplitudes over 40 dB above the unamplified transmitter signal. This signal appeared as a largely self‐sustaining embryo emission (EE) under the control of the transmitter signal. The phase of this EE signal in each NLA event was tracked with respect to a recorded phase reference. These phase studies showed that the accumulating phase of the offset EE signal is frequently interrupted by negative phase steps (‘N events’) which tend to reduce the offset frequency. Five of the NLA events during key‐down transmission were quenched by whistlers which themselves triggered free emissions at ½ƒBO. The theory of nonlinear wave‐wave interaction between the transmitter or input wave (IW) and the embryo emission is developed to explain these features. It is shown that coupling depends on the offset frequency δƒ and the ‘control frequency’ Fc: for δƒ > Fc the emission is effectively free; for δƒ < Fc, EE is controlled by IW. Curiously, Fc is determined by the EE amplitude (Bw) as Fc ∞ BW1/2, and is almost independent of IW amplitude. This control applies whether the emission was originally generated by IW or captured by it. Fc is determined from Bw measurement to be 60–120 Hz, which fits the observed behavior quite well. For δƒ < Fc a fraction of the phase‐bunched electrons are trapped by IW as they are detrapped by EE in the growth region. This superimposes a strong component oscillating in phase which can produce N events, effectively phase locking the low‐amplitude end of EE to IW. Amplitude fluctuations, δƒ, and Fc are interrelated in a complicated way which gives rise to short‐term instabilities and somewhat longer‐term stabilizing influences.

Narrow‐band VLF signals with a frequency separation of 100–130 Hz have been detected by a receiver aboard the S3‐3 satellite. The observations were made at L = 2.9 at an altitude of 5700 km. Satellite nadir was 45°N and 151°E. The radiation has the same characteristics as those reported for ground‐based observations of magnetospheric lines resulting from the nonlinear amplification of power line radiation. As is seen in ground‐based observations, the lines are not exact harmonics of the power system frequency, nor are they spaced at exactly 2 or 3 times that frequency. The frequencies of the three dominant lines were typically 7364, 7494, and 7598 Hz. During the time period of these observations the transportable very low frequency (TVLF) transmitter was performing magnetospheric wave injection experiments from a site in Central Otago, New Zealand. The modulation was 0.5 Hz frequency shift keying between 7350 and 8780 Hz. The narrow‐band signals detected by the S3‐3 satellite were observed in the 250‐Hz band above the lower frequency. The narrow‐band magnetospheric lines were apparently observed because power line harmonic radiation was amplified to detectable levels by a nonlinear interaction involving the TVLF signal. The most likely sources of the power line radiation are the 50‐Hz power grids in Tasmania, southeastern Australia, or New Zealand.

A high impedance system has been developed to make direct measurements of the atmospheric potential difference up to several thousand feet. A tethered balloon flown from Wallops Island, Virginia was used to loft a high voltage, insulated wire and a conducting collector in a test flight to 550 meters for two days of experiments in October 1980. The balloon was equipped with a payload to measure exact altitude, wind speed and direction, and other meteorological parameters. Electric potentials of 170,000 volts at 550 meters were measured. The collected currents which could be drawn through the wire by grounding the lower end were in the 10 microamp range indicating a system impedance of about 1010 ohms. This paper will describe the apparatus and details of these measurements.

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