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Whitey, K1VV, first published this
in the ARRL Hints & Kinks column March 1, 1999.
Fox
hunting was taking off locally, and upwards of two dozen fox hunters
were showing up Saturday mornings. This got me to thinking about how
to construct an inexpensive fox hunting beam for 2 meters, the Econo
Beam.
I built my
version of the beam using a 4-ft piece of 1x3-inch wood strapping
with 7/16-inch dowels to hold the #14 copper wire elements. The most
difficult and expensive part to secure was the 50-pf variable
capacitor for the gamma match. So I replaced the 50-pf variable
capacitor with a piece of RG-58 coax, the center conductor soldered
to the center conductor of the feed line and the braid to the gamma
match wire. The ARRL Handbook states that RG-58 has about 29 pf/ft.
Noting that the gamma match capacitor was about 25-pf, I cut a piece
of coax 15 inches long. I then set up the beam, and, using a MFJ-259
antenna analyzer, trimmed the element wires and the gamma match coax
1/8" at a time until II walked the beam onto 146 MHz, and obtained
an SWR of less than 1.2 to 1.
If you make a
mistake and cut off too much, it's simple enough to cut another
longer piece and start over.
If you don’t have
access to an MFJ-259, you can use an SWR meter. Even a typical HF
SWR meter will work well enough to get you in the ballpark, but you
may not be able to attain an indication of less than 2:1.
~Whitey, K1VV
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2-m Econo Beam
Gamma Match Details |
