July 6, 2019 – Darby, Montana
Six of us came to my Bunkhouse Road workshop from SE Darby hills, Hamilton and Alberton canyons
– Technicians, Generals, Amateur Extras
Some white-board work explaining the math in metric and inches
Our calculations were primarily done in metric (Ted’s slide rule prefers it)
300,000,000 meters per second / 147,000,000 Hz = 2.04 meters = 204 cm
a quarter wave antenna will be about 50 cm long, as will each radial
Measurements were done with metric + inch tape measure
Hardware:
dual binding post to BNC connector
BNC to SO-239 Adapter
choices of light and heavy electric fence wire
electric fence insulators
home-made pvc pipe insulators
Poly-pipe Tees and drip irrigation pipe for radial spreaders
After drawing, calculating, discussing, everybody went their own way with designs
Teamwork, creativity and fun marked the building, testing, adjusting phases
RigExpert AA-600 was the star of the show
Experimentation taught us
45-degree down angle on radials makes a big difference
live humans touching or too close to antenna being tested changes everything
It is exciting clipping a bit of wire, reassembling and watching the resonant center respond
thicker wire delivers broader sweet spot than thinner wire does
(brass rods would be better than fence wire)
(3/4″ copper pipe would be better than brass rods)
speed of electrical signal in a theoretical vacuum is different from real wire, real world
(actual antenna wire lengths are not exactly as calculated)
(component “velocity factor” could help the math match lengths we ended up with)
1:1 SWR on home-built UHF or VHF antenna is achievable with $10 worth of parts
antenna analyzers are peerless tools for antenna building
the alternative of trial and error with signal reports is a poor second, but more affordable
the RigExpert AA-600 that we used lists for $560
(the pain of a high price leaves while the quality of a product lasts, aka: I forgot what I paid)
We did not use much of its capability – a lower cost unit could have given us the SWR graph we needed
SO-239 was the chosen connector type because its counterpart PL-259 is the most common pre-fab coax antenna cable end in most areas … every truck stop and CB radio shop carries pre-made PL-259 coax cables in various lengths and the Internet has choices in just about any length you can wish for.
Having several people working together on a mutually interesting project is more fun, applies more minds to the challenges and is much more effective than the hermit ham going it alone.
This can be applied to any aspect of amateur radio you might be interested in.
Invite friends and acquaintences to explore FLDIGI, Mesh, fox hunting, CW, NVIS antenna building …
whatever tickles your fancy
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On a related subject, I visited the Hamilton Library, checked out their great, big, free meeting room and procedures for its use. It is available to any of us. It can be used during hours the main library is closed. Their booking calendar becomes available the first workday of the month for the next month, and does get a lot of bookings fairly soon. Nevertheless, there were a lot of July and August openings when I checked it out July 5th.
