11. B.
AT-800 Antenna Coupler Unit
(ACU)
- Teardrop H-Field (See Figure 11-3
and Table 11-4.)
The AT-800 ACU contains two signal-sensing elements and the first two
stages of signal amplification and frequency selection.
An orthogonal
pair of ferrite rod loop antenna elements are used to sense the
H-(magnetic) field component of the Omega/VLF signals. Since loop
antennas display an inherent directional sensitivity pattern, orthogonal
positioning of the two loops provides omnidirectional coverage.
Moreover, through electronic steering of the loop reception pattern, a
6-dB
signal-to-noise gain can be achieved. Also, loop antennas exhibit
relative immunity to noise generated by airframe electrostatic
discharges (e.g., precipitation-staticdischarges).
Integral preamplifiers comprise the amplification stages. These two
stages amplify the received signals sufficiently to allow the signals to
be cable-transmittedto the OZ-800 RPU without significant
signal-to-noisedegradation.
A BITE capability whereby test signals are
introduced directly into the ferrite rods, allows monitoring of ACU
sense elements and preamplifier stages.
Electromagnetic interference (EMI) protection for the ACU is provided by
a combination of filtering and shielding.
The frequency response of the
ACU provides rejection of any signals outside the Omega/VLF frequency
band. All
internal circuitry in this unit is shielded by a solid
metallic shield whose electrical reference point is floating with
respect to the airframe.
A circumferentially grounded Faraday shield is
provided in the cover for the
ACU.
./
\
!2
AD-1 5620
AT-800 Antenna Coupler Unit
Figure 11-3
22-14-00
Page 198.166
Apr 15/93
Useor disclosure of information onthispage issubject totheresttictions on the title page of this document.
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