I get the feeling you don't believe DF can be done with any usefulness on
160. You might be right and you might be wrong, but you seem to have tossed
out the study I mentioned assuming it has no validity at all for 160. I
think that's extreme.>>
I don't know the study so I can neither accept it nor toss it out. But I
certainly would raise my eyebrows at anyone who used a single loop to
measure arrival direction or angle of skywave signals.
There are a great number of well-intentioned studies with unreliable
conclusions that are accepted, such as the LF "electric field blanket" study
using conclusions reached by raising height of an alleged "voltage probe".
All I'm saying is I'm very familiar with all the problem involved in using a
single loop or arrays of elements to discriminate-against or focus-on
sky-wave 160 meter signals, and the null is too narrow and the loop response
is much too broad and much too even to use a single loop to reliably do
anything on skywave.
The loop has multiple shortfalls in this application. It can't hear weak
signals or sort out multipath because it has almost no directivity. It has a
narrow response hole through the axis, and a tilted polarization that runs
the entire range of vertical to horizontal as we look at it from different
points with almost equal response levels.
It is also heavily influenced by the earth, the feedline connection, and
anything else around it and this skews the true null direction off axis.
Longer distance DX often come in via two or more paths at once. I can watch
VK signals arrive from NW, W and/or SW at the same time. JA's often are via
SW and NW paths. Closer stations very often come in from both high and low
angles at the same time.
If there is multipath, and there almost always is, a loop null would be very
unlikely to align with any of the actual paths. If it did, it would be a
fortunate circumstance rather than good measurement. The worse part is, it
could easily show us a wrong direction null and make us think something is
happening that isn't.
We really need a narrow HPBW, and antenna removed from local influences, and
a clean predictable pattern to tell skywave direction. A loop out back on
the picnic table won't fit that criteria, even if it does show a null.
73 Tom
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