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Re: commutating antennas



On Fri, May 03, 2002 at 10:47:29AM -0400, Howie DeFelice wrote:
> Isn't this what they did for the VHF antennas on ATS-3 ??

The VHF antennas on ATS-1 and ATS-3 were actually cylindrical phased
arrays of coaxial dipoles, which gave the satellite its squid-like
appearance.  There were eight preamplifiers with analog (L-C) phase
shifters with the outputs summed and fed to a downconverter, amplified,
upconverted and fed to eight amplifiers with similar phase shifters. 
The phase shifters would despin the beam, and if turned off, an
omnidirectional pattern would result.  ATS-1 had a similar microwave
despun phased array, while ATS-3's microwave antenna was mechanically
despun, as it done with modern geosynchronous satellites.

The difference between the VHF systems on the two satellites was that
ATS-1 was hard limiting, while ATS-3 was linear.

I did much of the antenna design plus the system integration on the VHF
repeater system on ATS-1 at Hughes in 1965-66.  Matching the phases of
those eight receiver/transmitter modules was a real PITA.  Fortunately
Hewlett-Packard introduced the Vector Voltmeter as we were starting to
test the system.  We were unable to get timely delivery of one, since
military contracts had priority over NASA, but I was able to borrow a
Vector Voltmeter from the local H-P salesman and completed the phase
measurements over a weekend.  The actual phase matching was done by
varying the length of the coaxial cables between the T/R modules and
the i.f. assembly.


73,

Bob N7XY
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