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George Chaney W5JTL-SK published an article in Ham Radio magazine
October 1985 on how to make virgin PTFE Flanged bushings and the
required tooling for insulating elements in long boom Yagi’s.
When George began selling the
PTFE bushings and tooling some time later my friend and EME partner
Joe Burke WA8OGS bought a kit and built a 903 MHz antenna.
When a storm brought down the antenna some 20 years later, Joe
found the elements still firmly in place and the PTFE insulators
looked like new! Since we were
planning to build a new EME array Joe challenged me to find a source
for Virgin PTFE flanged bushings suitable for 3/16” diameter elements.
I found a source and bought a run of 1,000 flanged PTFE
bushings. We sent a kit of the
flanged PTFE bushings, the installation tooling and a flash drive with
a video showing the process of installing the elements in a boom to
Hartmut DG7YBN.
K1FO furniture bushings with metal keepers for 3/16” elements
G0KSC furniture bushings in undersized holes for ¼” elements
DG7YBN PTFE flanged bushings for 3/16” elements
Photo showing Flanged PTFE bushings Holding a 3/16” element in a 1”
square boom. If you look
closely and compare the expanded PTFE bushings with the new ones
sitting in the boom you can almost see that the flange is a bit
thinner and the inside portion is mushroomed.
We have to cutoff the flange to remove expanded PTFE bushings
from the boom.
We all appreciate having PTFE insulation in Coax and Coax
connectors, We know that it
is an excellent insulator and that it will be heat resistant when we
go to solder the connections.
But the property of virgin PTFE that George Chaney focused on
was material creep. When
the virgin PTFE 1/8” center
hole is expanded to 13/64” with a tool to insert a 3/16” element it
will try to creep back to the original size and firmely grip the
Yagi element. This happens
quickly so George cautioned the antenna assembler to adjust element
positions that same day as longer the time the firmer the grip will
become.
YBN: Ideally elements are marked at center and half booms width plus
length of head of the PFTE bushings either side of the mid mark to be
able to adjust their position while or instantly after pushing them
in.
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