Hawkeye VLF

This experiment measured electric and magnetic fields using a 42.45-m electric dipole (tip-to-tip) which extended perpendicular to the spin axis and a search coil antenna deployed 1.58 m from the spacecraft. The electric field spectrum measurements were made in 16 logarithmically spaced frequency channels extending from 1.78 Hz to 178 kHz, and dc electric fields were also measured. The bandwidth of these channels varied from 7.5% to 30% depending on center frequency. Channel sensitivity and dynamic range were 1E-6 V/m and 100 dB, respectively. A wideband receiver was also used, with two selectable bandwidth ranges: 0.15 to 10 kHz or 1 to 45 kHz. The magnetic field spectrum was measured in eight discrete, logarithmically spaced channels from 1.78 Hz to 5.62 kHz. The bandwidth of these channels varied from 7.5% to 30% depending on frequency. The dynamic range was 100 dB, and the sensitivity ranged from 0.1 nT at 1.78 Hz to 3.4E-4 nT at 5.62 kHz. The wideband receiver described above could be used with the magnetic antenna. Each discrete channel was sampled once every 11.52 s.

Additional details from NASA's CDAWeb:

Electric Antenna

The electric antenna on HAWKEYE consisted of two extendible beryllium copper
elements 0.025 inch in diameter which could be extended to a maximum tip-to-tip
length of 42.7 m. Except for the outermost 6.1 m of each element, which had a
conducting surface, the antenna was coated with Pyre-ML to electrically insulate
the antenna from the surrounding plasma. The insulating coating was required to
insulate the antenna from the perturbing effects of the plasma sheath
surrounding the spacecraft body. At high altitudes, the thickness of the plasma
sheath surrounding the spacecraft body was quit large, on the order of 9 m.
Since the conducting portion of the antenna must extend beyond the plasma
sheath, it was necessary that the antenna be rather long, at least 30 m.
tip-to-tip. The antenna mechanism used on HAWKEYE was the Dual-Tee extendible
antenna manufactured by Fairchild Industries. The antenna length was 42.49
meters after final deployment until the last orbit, when an attempt was made to
retract the antenna to reduce the spacecraft drag.

Magnetic Antenna

The magnetic antenna for this experiment consisted of a search coil with a high
permeability core mounted on a boom approximately 1.5 m. from the centerline of
the spacecraft body. The boom was a three element telescoping device developed
at the University of Iowa. The boom supporting the flux gate magnetometer on the
opposite side of the spacecraft was the same type. Both booms were extended
simultaneously by an electric motor.

The search coil core was .305 m. long and was wound with
approximately 20,000 turns of copper wire. The axis of the search coil was
parallel to the spin axis of the spacecraft. A preamplifier was located with the
sensor to provide low-impedance signals to the main electronics package in the
spacecraft body. The frequency range of the search coil antenna was from 1.0 Hz
to 10.0 kHz.

Electronics

The potential difference between the electric antenna elements was amplified by
a high input impedance differential amplifier to provide a 0 to 5 volt analog
voltage, V-Diff, to the spacecraft encoder. As the spacecraft rotated the
potential difference between the antenna elements varied sinusoidally at the
spacecraft rotation rate, with an amplitude proportional to the electric field
strength and a phase determined by the direction of the electric field. The
frequency response of the differential amplifier was 0.05 Hz to 10 Hz and
included the entire range of spin rates expected as the antenna was deployed.
The V-Diff signal was sampled 6 times each frame by the encoder. The gain of the
differential amplifier could be controlled by command to provide dynamic ranges
of +/-0.5 and +/-8.0 volts for the antenna potential difference measurements.

Signals from the electric antenna in the frequency range from 10 kHz
to 200 kHz were analyzed by the narrow band step frequency receiver. The primary
purpose of this receiver was to provide very good frequency resolution in the
neighborhood of the electron plasma frequency and upper hybrid resonance
frequency. The step frequency receiver consisted of 8 narrow band filters (+/-5%
band-width) which were sequentially switched into a log compressor. The log
compressor provided a 0 to 5 volt analog voltage, SFR, to the spacecraft
encoder. The switch (S4) position was controlled by clock lines from the
spacecraft encoder and was stepped through 8 frequencies, 13.3, 17.8, 23.7,
31.1, 42.2, 56.2, 100, and 178 kHz, at a rate of four frequencies per telemetry
frame (5.76 seconds). The log compressor provided a 0 to 5 volt analog voltage,
SFR, to the spacecraft encoder which was proportional to the logarithm of the
signal strength over a dynamic range of 100 db.

The 8-channel spectrum analyzer provided relatively coarse frequency
spectrum measurements of both electric and magnetic fields over a broad
frequency range of 1.0 Hz to 10.0 kHz. The primary purpose of the 8-channel
spectrum analyzer was to provide field strength measurements to complement the
high-resolution frequency-time spectra from the wide-band receiver.

Switches S1 and S2 were controlled by clock lines from the spacecraft
encoder and commutate the filter outputs to two log compressors which provided
field strength measurements SA-1 and SA-2 (0 to 5 volts) to the spacecraft
encoder. These outputs were sampled twice per telemetry frame. Switch S3, which
was controlled by a clock line, commutates the electric and magnetic field
signals to the 8-channel spectrum analyzer.

Approximately every 5 minutes the impedance of the electric antenna
was determined at a frequency of 17 Hz by driving a small AC current into the
antennas and measuring the resultant voltage on the antennas with the 8-channel
spectrum analyzer. The 17 Hz oscillator was gated on for 1 frame out of every 64
frames by a clock line.

Immediately following the impedance measurement the pulser circuit
produced a 10 volt pulse with a duration of 20 micro- seconds. This pulse was to
stimulate local plasma resonances, such as plasma oscillation, from which the
electron density could be determined. A pulse of +10 volts was applied to one
antenna element and a -10 volt pulse was applied to the opposite antenna
element. The pulser was switched on by command. The pulser was on when the
experiment was in VLF45 mode and off when the experiment was in the VLF10 mode.
The pulser voltage was coupled to the antenna through a 220 pf capacitor which
would have allowed some meaningful data to be obtained from the experiment even
if the pulser output were to short to ground. The pulse was applied at the end
of the impedance measurement frame.

The potential difference between the electric antenna elements was amplified by
a high input impedance differential amplifier to provide a 0 to 5 volt analog
voltage, V-Diff, to the spacecraft encoder. As the spacecraft rotated the
potential difference between the antenna elements varied sinusoidally at the
spacecraft rotation rate, with an amplitude proportional to the electric field
strength and a phase determined by the direction of the electric field. The
frequency response of the differential amplifier was 0.05 Hz to 10 Hz and
included the entire range of spin rates expected as the antenna was deployed.
The V-Diff signal was sampled 6 times each frame by the encoder. The gain of the
differential amplifier could be controlled by command to provide dynamic ranges
of +/-0.5 and +/-8.0 volts for the antenna potential difference measurements.

Signals from the electric antenna in the frequency range from 10 kHz
to 200 kHz were analyzed by the narrow band step frequency receiver. The primary
purpose of this receiver was to provide very good frequency resolution in the
neighborhood of the electron plasma frequency and upper hybrid resonance
frequency. The step frequency receiver consisted of 8 narrow band filters (+/-5%
band-width) which were sequentially switched into a log compressor. The log
compressor provided a 0 to 5 volt analog voltage, SFR, to the spacecraft
encoder. The switch (S4) position was controlled by clock lines from the
spacecraft encoder and was stepped through 8 frequencies, 13.3, 17.8, 23.7,
31.1, 42.2, 56.2, 100, and 178 kHz, at a rate of four frequencies per telemetry
frame (5.76 seconds). The log compressor provided a 0 to 5 volt analog voltage,
SFR, to the spacecraft encoder which was proportional to the logarithm of the
signal strength over a dynamic range of 100 db.

The 8-channel spectrum analyzer provided relatively coarse frequency
spectrum measurements of both electric and magnetic fields over a broad
frequency range of 1.0 Hz to 10.0 kHz. The primary purpose of the 8-channel
spectrum analyzer was to provide field strength measurements to complement the
high-resolution frequency-time spectra from the wide-band receiver.

Switches S1 and S2 were controlled by clock lines from the spacecraft
encoder and commutate the filter outputs to two log compressors which provided
field strength measurements SA-1 and SA-2 (0 to 5 volts) to the spacecraft
encoder. These outputs were sampled twice per telemetry frame. Switch S3, which
was controlled by a clock line, commutates the electric and magnetic field
signals to the 8-channel spectrum analyzer.

Approximately every 5 minutes the impedance of the electric antenna
was determined at a frequency of 17 Hz by driving a small AC current into the
antennas and measuring the resultant voltage on the antennas with the 8-channel
spectrum analyzer. The 17 Hz oscillator was gated on for 1 frame out of every 64
frames by a clock line.

Immediately following the impedance measurement the pulser circuit
produced a 10 volt pulse with a duration of 20 micro- seconds. This pulse was to
stimulate local plasma resonances, such as plasma oscillation, from which the
electron density could be determined. A pulse of +10 volts was applied to one
antenna element and a -10 volt pulse was applied to the opposite antenna
element. The pulser was switched on by command. The pulser was on when the
experiment was in VLF45 mode and off when the experiment was in the VLF10 mode.
The pulser voltage was coupled to the antenna through a 220 pf capacitor which
would have allowed some meaningful data to be obtained from the experiment even
if the pulser output were to short to ground. The pulse was applied at the end
of the impedance measurement frame.

本实验采用一个42.45米的电偶极子（端对端）来测量电场和磁场，该偶极子垂直于自旋轴延伸，并在距离航天器1.58米处部署了搜索线圈天线。电场频谱测量是在16个对数间隔的频率通道中进行的，频率范围从1.78赫兹到178千赫兹，同时测量了直流电场。这些通道的带宽根据中心频率的变化从7.5%到30%。通道灵敏度及动态范围分别为1E-6 V/m和100 dB。此外，还使用了一个宽带接收器，具有两个可选的带宽范围：0.15至10 kHz或1至45 kHz。磁场频谱是在1.78赫兹到5.62千赫兹的八个离散、对数间隔的通道中测量的，这些通道的带宽根据频率的变化从7.5%到30%。动态范围为100 dB，灵敏度从1.78赫兹的0.1 nT到5.62千赫兹的3.4E-4 nT不等。上述宽带接收器可用于与磁场天线配合使用。每个离散通道每11.52秒采样一次。来自NASA CDAWeb的附加详细信息：