k3lr at telerama.pgh.pa.us
Tue Jul 27 16:21:23 EDT 1993
Several years ago I had a Hygain Hytower which used PVC in the upper
section of tower to isolate the 80 meter whip. When I installed a
loading coil (per Hygain) for 80 CW, the PVC caught on fire when using
the SB-220! The black color can cause the PVC to become less of an
insulator as well. Sometimes they use carbon to get the color black.
I installed a teflon insulator and never had any problems.
I also tryed PVC in an old Alpha vapor cooled amplifier. The 70V hose
broke during the ARRL DX contest. I ran to the hardware store and
replaced it with black PVC. When I turned the amp on....bang! The
PVC could not stand the DC voltage!
75 ohm CATV cable works very well on the low bands with 75 to 50 ohm
broadband XMFRs. The W2FMI units have very low loss and are good to
50 MHz. ICE also has heavy duty units that I use without problems.
The loss with a XMFR on either end of 3/4" CATV 75 ohm line is better
than 1/2" 50 ohm heliax by itself.
WR3G and I just installed some more Phillystran on the 10 meter tower.
The guy wires are at 32.5', 65.5' and 99.5'. The 7 ele beams are
mounted at 33', 66' and 100'. Even with insulated sections such as
the 1st length being 4', the next 6', 6', then 12', 12' and so forth
the VSWR varied when you turned the antennas and the pattern was very
poor. I thought we had broken the guy wires more than enough! I
installed 60 feet of Phillystran on each guy and now the VSWR is good
and the pattern is great!
I'm not ready to give up insulators (see Aug QST) but if your antennas
are mounted close to guy wires, you might want to rotate them and
check your VSWR.
The new clamps on the Phillystran seem to work well, we'll see how
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