The activities at Virginia Polytechnic Institute and State University in preparation for the February 1993 launch of ACTS are summarized. ACTS propagation terminals (APT) are being constructed to receive the 20 and 27.5 GHz ACTS beacon signals. Total power radiometers operating at the same frequencies are integrated into the terminal for use in level setting. Recent progress and plans for APT's are reported

Pratt, Tim

Stutzman, Warren L.

English

NASA Technical Reports Server

N93°26484
ACTS PROPAGATION TERMINAL UPDATE
Warren L. Stutzman
and
Tim Pratt
Satellite Communications Group
Bradley Department of Electrical Engineering
Virginia Polytechnic Institute and State University
Blacksburg, Virginia 24061-0111
Abstract - This paper summarizes the activities at Virginia Tech in
preparation for the February 1993 launch of ACTS. ACTS propagation
terminals (APT) are being constructed to receive the 20 and 27.5
GHz ACTS beacon signals. Total power radiometers operating at the
same frequencies are integrated into the terminal for use in level
setting. This paper reports on recent progress and plans for APTs.
i. INTRODUCTION
NASA is providing earth terminals for seven propagation
experiments across the U.S. Virginia Tech, under a NASA contract,
has designed and constructed a prototype ACTS propagation terminal
(APT). The prototype is currently undergoing final testing.
Construction of the production units will begin this summer. A
common hardware and software set reduces the cost of the terminals
and improves data collection reliability. Individual experimenters
will be able to focus on their experiments and will not have to
design and construct their own terminal.
The terminal uses a single antenna with a waveguide diplexer
for frequency separation followed by separate 20 GHz and 27.5 GHz
receivers. Co-polarized attenuation and scintillations at these
frequencies are to be measured. A simplified block diagram of the
APT is shown in Fig. i.
The Olympus experiment at Virginia Tech offered an excellent
test bed for many of the systems to be used in the APT. The four
beacon receivers at 12.5, 20, and 30 GHz, which were designed and
constructed at Virginia Tech, have been very stable and reliable.
The simple total power radiometer, which is built into the Olympus
terminals, has proved to be extremely accurate. The ACTS RF system
differs from that used in Olympus. A complete RF downconverter
block replaces discrete components. This greatly reduces the time
required for construction of production terminals. The IF
(Intermediate Frequency) and DACS (Data Acquisition and Control
System) subsystems are very similar to those used in the Olympus
project. The ACTS digital receiver is totally different from the
analog FLL receiver used in Olympus, which required a long time to
develop and is rather complex.
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ACTS propagation terminal update

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