[222mhz] Cost/performance comparisons of transmission lines.

[Dr. Gerald N. Johnson, electrical engineer]

The W0YL repeater has been using a run of 9913 for close to 15 years.
Nearly 200 feet up a water tower. In recent visits, it has shown a
higher SWR than original, though the repeater doesn't seem to have lost
performance and range or to be showing desense typical of water in the
coax or a connector. When KI0Q put that coax up, he waterproofed the
connections the say way he waterproofs aluminum underground service
wires with several layers of alternating Scotch 33 and Scotchkote. Today
there are heatshrink kits that would be at least as effective. 9913
can't be allowed to breath or it will gather moisture and there will be
condensation and that will cause loss that may not show up as SWR
(especially at 445 MHz).

Unfortunately the repeater is off the air right now because a paint crew
is cleaning and painting the water tower. I fear the 9913 won't survive
their handling and will need to be replaced. 7/8" foam heliax would be
nice, probably used 1/2" foam heliax may be used IF we can continue to
get access to the water tower to care for the antenna, feedline, and
repeater. We may have to move with the post 9-11 security restrictions
on a US Government facility.

I've been using 1/2" and 3/4" CATV 75 ohm cable at home for decades with
fine results, but I build my own connectors that use a large connecting
area on the aluminum shield with aluminum conductor grease and lots of
Scotch 33 for water proofing.

73, Jerry, K0CQ
-- 
Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
Reproduction by permission only.