Date: Sat, 6 Apr 2013 03:17:15 -0000
From: "John G." <af5cc@fidmail.com>
To: "Dan Hearn" <n5ardxcc@gmail.com>
Cc: towertalk@contesting.com
Subject: Re: [TowerTalk] Vertical comparison question
Hi Dan
How lossy are traps really? I have seen so many diffrent figures on how bad
they are or aren't
73 John AF5CC
## I literally melted two trap vert ants back in the mid 70s. .... with 1900
w out on cw.
A buddy had a TA-33 jr... thay went screwy one day..so we took it down off his
tower.
Slid the covers off the traps on the DE...and the forms that the coils are
wound on, were
completely melted ! It look like somebody had run a propane torch up and
down it.
He was using a SB-220 at the time...1200 w pep out, ssb only.
## telrex used fixed HEC / centralab style HV, NPO TX caps on their trapped
yagis...and they
too are a pita. Phil, K5pc, was always getting Telrex to send him more caps,
etc.
## fixed ceramic vac caps and 6 ga cu wire or .187” tubing might work for
traps, but heavy.
## The real answer is probably the multiband stepir verticals. No traps,
and it can be tuned dead on
right across the entire hf spectrun, like 7-54 mhz. But it would require
radials.
## seco systems makes motor driven compressible coils, with a 2:1 uh range.
IE: 6-12, 10-20, etc.
These are used on verticals to resonate anywhere within ONE band, like 80m.
they also make em, so
when the coils are fully expanded, they short out each coil, taking it right
out of the circuit ! that way, it
will work on a 2nd band, like a monoband vert.
## resonant radials, esp for 40m, can be a pita in some cases. back in the
70s, I used a 20’ tv mast
on the roof, and the trap vertical above that. Then loads of room for 40m
radials. But the roof was 29’ tall,
and the very top of the vertical was 70’ above ground. No easy feat, but
doable.
the step IR vert is worth checking into.... but again, requires radials.
radial laid on a roof can also be bent at the
ends to make em fit in. that works, but I used insulated wire for the
radials.
F-12 also makes some lossless vert arrays, with T bars..... capacity hats.
Jim VE7RF
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|