Several years back we had the discussion about choke ring antennas.
Dr Thomas Clark - retired NASA - Goddard Space Flight Center - I believe
he was head of the VLBI project - made a simple choke ring antenna with
an electrical junction box.
I made 3 sets using pie plates. I promised somebody the pictures and
forgot it until now. The pictures are hosted at
http://kc0onr.com/Brian/_MG_0668.jpg
http://kc0onr.com/Brian/_MG_0669.jpg
I made these units because were I lived was surrounded by mountains 3/4
around my property and I was at 720 feet elevation and the mountains
varied from 1000 to 1200 feet. I had a problem that my receivers jumped
positions several times and I suspected a multi path problem. I made
the first antenna using some RF adsorbent material around the antenna.
Helped. After making the choke rings, the problem went away. The other
two units were used for carrier phase surveying. With the Motorola
Oncore VPZ unit and Waypoint's GrafNav software I could get resolution
down to a little under an inch.
Brian KD4FM
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