[Antennas] SWR Isn't Enough - Working in a high SWR setting
Mike J Maloney
[email protected]
2002年4月28日 22:34:31 -0500
HI Jim,
Comments inserted below.
Would you mind sharing some
> tips on
> how to get the most out of ladder line? For instance, could you
> give me
> ideas on what to consider when making long runs of 450 ohm windowed
> ladder
> line?
For long runs, I would not get the 450 ohm "windowed" ladder line. It is
more of a glorified twin lead using copper clad steel for the conductors.
For lowest loss make your own from 1/2" polyethylene irrigation tubing
spacers or get from www.w7fg.com.
What should it not be near? How does one get it around rain
> gutters?
> etc. What tips do you have for stand off insulator ideas?
Black polyethylene or plexiglas stand-offs, or nylon weed eater line thru
spacers to tie off or hold taut. Keep 2-3 times or more spacing away from
metal downspouts, guttering, metal window screens, etc.
>> Also, any tips on 'feed thru' approaches (e.g. into the shack).
Bring it thru the wall(if composition material) to interior wall, using
binding posts or banana jacks for quick disconnect for lightning
isolation. If squeemish about going thru wall, replace a window pane
with plexiglas panel fitted with banana jacks. Bring open wire feeders
direct to balanced tuner output. Coax from 50 ohm tuner input to rig.
Balun not needed with the proper coupler. If not, use a coil choke
balun on low Z input side.
I believe big closed horizontal loops make the best all band simple
antennas. See April 2002, QST p.47. If space and conditions dont allow a
big loop, then a center fed doublet is next. Try to get at least a
half-wavelength of antenna (half) plus feedline at the lowest frequency
for best efficiency, as high as you can in the air.
> remote switching so as to be able to insert different matching stub
> lengths
> before transitioning to coax?
Not necessary.
If you use underground conduit what
> else
> can/cannot go in the conduit with the ladder line?
Have not tried this. If I did, I would not run anything with the ladder
line. Would use seperate 4" PVC and do the best I could to keep water
from getting into the conduit. Perhaps dry air under pressure.
>> Could you recommend a good reference book or other resource on using
> ladder
> lines?
ARRL or E&E Handbooks prior to 1960, the older the better. Only
commercially produced true ladder line (dielectric being 95% air) I know
of is from www.w7fg.com
73 es good luck,
Mike, ac5p