http://www1.vcars.org:8040/carl/nvis.html 有更為簡潔的nvis介紹與天線製作方式.
near vertical incident scattering antenna
construction of nvis antenna
author: dr. carl o. jelinek
email:
cjelinek@ix.netcom.com why use an nvis antenna?
usable on all hf ham bands.
to work the skip zone {out to about 1000 miles}.
areas behind obstructions and in dense foliage.
to hear the near in stations just beyond ground wave range.
great for field day and contesting as a “gap filler” antenna.
easy antenna for hf mountain topping and camping trips to get rf out of deep canyons.
limitations
must work frequencies below the maximum usable frequency (muf).
this is not a dx antenna.
needs to use an antenna tuner for good match.
power limited to about 200 watts.
beverage mode losses limit achievable gain.
nvis antenna dimensions
parts list
2 ea 1.5" pvc pipes 7.5' long
1 ea 1.5" pvc coupling
1 ea 1.5" pvc cap
4 ea egg type insulators
5 ea brass screws, nuts and washers to fit coaxial fitting
1 ea so-239 or ug-266 female panel mount connector with solder pot center pin
5 ea stakes (one at the mast center)
4 ea heavy solder lugs to fit brass screws
~150' antenna wire (i like braided ground strip kind)
~60' nylon rope
coax to rig as much as you need. run it up the center of the pvc pipe mast and connect to the panel mount connector.
construction of nvis antenna
(圖片請看原文)
drill pvc cap to accept so-239 and 4 screws and nuts
mount so-239 to pvc cap with screw heads down
cut off the head of a brass screw
solder a brass screw to center post of so-239
cut antenna wires to length plus a little
fit one end of each wire with solder lugs
fit the other with the egg insulators
install wires to so-239 using brass nuts and washers {as shown in the figure}
erect antenna (2 men ~ 5 minutes)
tune antenna match for minimum vswr (also could adjust mast height and wire lengths)
