This very low frequency (VLF) receiver on Injun 5 was designed to study both electric and magnetic components
(both phase and amplitude) of VLF signals. The direction of signal propagation could be determined and used to assist in
identifying the origins of various VLF signals. The observations of antenna impedance for the electric antenna (ECA) were
needed to study characteristics of such an antenna operating in a plasma. There were two antennas, one driving a magnetic-field
component receiver (MCR), and the other driving two electric-field component receivers (ECR). The MCR operated from a
55.9-cm-diameter loop antenna (MCA), and the ECRs operated from an antenna consisting of two 20.3-cm-diameter aluminum spheres
mounted 2.85 m apart on opposite sides of the spacecraft (S/C). Both the MCA and ECA were mounted on booms to reduce interference
from the S/C. Within a few weeks after launch, the S/C was despun and magnetically stabilized so that nominally, the antenna axes
and the magnetic field line through the S/C were orthogonal. In the northern hemisphere, the MCA supporting boom was inclined
earthward. Both the MCR and ECR operated from 10 to 30.E3 Hz. Also operating from the ECA was a narrow-band step frequency
receiver (ECR 2) which operated through filters with center frequencies at 7.5, 10.5, 22, 52.5, 70, and 105 (plus or minus 7.5 %)
kHz. Supplementary to these three receivers and two antennas were (1) a special circuit that could measure phase and amplitude of
the impedance on the ECA between 20 and 2.E3 Hz and (2) an electron gun used to bias the ECA. The MCR and ECR 1 observed and
telemetered (on a 0.8-W, 400-MHz channel) analog, broadband data in real time, when the S/C was in telemetry range of a ground
station. When observing with the impedance circuit on, impedance measurements required 8 of each 30 s of wideband observing time.
The signal strength values from the ECR 2, and separately from both the low (0.03 to 0.65 kHz) and high (0.3 to 10 kHz) ranges of
the ECR 1 and MCR, were recorded on the S/C tape recorder and comprised the digital data for this experiment. In this experiment,
the digital data were observed and recorded over a 30-s cycle within which the signal amplitudes from the two low-frequency steps
of the ECR 2 were observed every 4 s (1-second duration) and the other frequencies observed every 8 s. When the impedance circuit
was on, eight samples of the step receiver data were not observed during each 30-s cycle. Experiment performance was nominal. Failure
of the S/C power regulator early in the mission limited operation to some extent, but nominal data were obtained until May 29, 1970.
Principal telemetry sites for the data through May 1970 were in Iowa and Alaska. Further experiment details may be found in D. A.
Gurnett et al., J. Geophys. Res., v. 74, n. 19, p. 4631, 1969.