Topband: Sloping full wave pentagon loop

Bill Tippett btippett at alum.mit.edu
Tue Jan 4 08:44:54 EST 2005


W0DLE wrote:
 >I know a horizontal loop makes a good NVIS radiator, but with the sloping
ground and sloping wire. will I get a medium TO angle?

         Chuck, that would be extremely complex to model, which
is the best way to answer your question.  However, my guess
is that most of your radiation is high angle.  To get good
low angle radiation from any horizontal antenna, it needs
to be in the order of 1/2 wavelength high, which is ~270' on
160.  Even with your sloping ground, I suspect the antenna
"sees" the ground directly underneath much more than the
distant terrain, thus creating mostly create high angles.

         However, that does not mean your antenna cannot work DX.
I have an inverted-V with the apex at about 100' with the ends
at about 40'.  Peak radiation is straight up, but for angles
of 40 degrees and up, it is better than my vertical array.
See the elevation plot at the top of this page:

http://users.vnet.net/btippett/new_page_10.htm

Blue is the inverted-V and black is the 3 element vertical array.
There are times when the inverted-V is +10 dB over the vertical,
even for DX signals, indicating some sort of high angle
propagation mode (most often at sunrise and sunset).

         Ideally it would be nice to shunt feed your tower, decouple
your loop, and be able to switch between the two depending on
which is best at any time.  But even if you cannot do that you
should still do OK with the loop when conditions favor high
angles.

                                                 73,  Bill  W4ZV




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