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Fall 2004 Issue |
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Adding to an Arrow Satellite Antenna for Easy AO-51 Tracking |
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By Dr. Robert Suding,* WØLMD |
The Arrow antenna mounted on a tripod. |
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The Arrow antenna systems can be used as they come for picking up the FM signals from AO-51—if you can hold the antenna in the correct direction for up to 15 minutes and don’t mind listening to a very weak signal. However, by tripod mounting the Arrow (it’s already tapped for a 1/4-20 tripod bolt) and adding bearing indicators and a pre-amplifier, you wind up with a real working antenna system. It’s ideal for mobile and portable use and works great for those who are stuck with anti-antenna covenants. The first thing to do after buying an Arrow antenna is to get a small, lightweight camera tripod (photo 1). I got mine from the local Best Buy store. It was designed for the latest generation of small digital video cameras. Taking the sponge rubber grip off the reflector end of the antenna will reveal four 1/4-20 tapped holes. I used a hole that resulted in the 432-MHz elements being horizontal and the 144-MHz elements being vertical. The 1/4-20 bolt on the tripod can be attached to the Arrow now, but mounting it this way makes a very nose-heavy antenna, and a lightweight tripod is prone to tipping over. Thus, I took an 18-inch length of 5/8-inch aluminum tubing from an old discarded antenna, filled it with a length of 1/2-inch steel rod, and added a plastic end cap so it would look neat. I next inserted the tubing with rod about 2 inches into the reflector end of the Arrow, and I noticed the improvement in balance. I drilled a 3/8-inch hole in the 5/8-inch tubing and steel rod where the Arrow beam attaches to the tripod so that this counterbalance is locked onto the beam. I also notched the bottom end of the sponge-rubber handle where it would interfere with attaching to the tripod. The beam can still be handheld if desired.
I found the signal from AO-51 too weak for
comfortable listening on my ICOM 910H or Kenwood TS-2000, so I added an
inexpensive Hamtronics 432-MHz preamplifier (photo 2). This preamp is not
moonbounce quality, but it amplifies the very weak signal from AO-51
enough such that AO-51 comes in S9 or better when the antenna and the
satellite are pointing at one another. A short piece of low-loss 50-ohm
coax runs between the 432-MHz connector on the Arrow and the input to the
preamplifier. A longer piece, about 18 feet long in my case, runs between
the output of the preamplifier and the antenna end of a bias tee. The bias
tee puts 12 volts up the coaxial line to power the preamplifier.
Click here to return to Fall 2004 highlights Click here to subscribe to VHF _________________ © Copyright 2004, CQ Communications, Inc. All rights reserved. This material may not be reproduced or republished, including posting to a website, in part or in whole, by any means, without the express written permission of the publisher, CQ Communications, Inc. Hyperlinks to this page are permitted.
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