Fading can be a problem on 160. When it is due to polarization rotation
of the incoming signal, a circularly polarized receive antenna can
eliminate it. An elliptically polarized antenna can reduce it. I'll call
both CP.
I describe a CP antenna for 20 meters here:
https://www.eham.net/community/smf/index.php?topic=143601.0
A compact CP antenna for 160 can use the same principle but with a tuned
loop replacing the dipole. I modeled an untuned square loop 3 feet on a
side. Optimizing for minimum axial ratio at 20 degrees elevation angle
yielded an antenna center height of about 71 feet and a loop tilt of
about 23 degrees.
Geometry image (height above the X-Y ground plane not to scale):
https://i.postimg.cc/QN4dtMZd/geom.png
Axial ratio plot:
https://i.postimg.cc/6pQSQ9wt/cp.png
For this model I used Hagn generic ground constants for pastoral ground
at 1.8 MHz (permittivity = 20, conductivity = 3.6 mS/m). Constants for
other ground types are here:
https://k6sti.neocities.org/hfgc.htm
I don't know whether this idea has merit. Fading on 160 may be mostly
due to factors other than polarization rotation. A tower supporting the
loop may interfere, as may other nearby antennas. It may be difficult to
adequately decouple the loop feedline. Your local ground constants might
be quite different than those you model.
I haven't operated on 160 for many years. But I recall the frustration
of waiting for a callsign during a slow fade only to have it disappear
into the noise. Maybe this antenna can help.
Brian
_________________
Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
| 
