VOACAP does indeed predict optimum arrival angle for any particular
path, but that's based upon statistical averages -->by month<-- and has
no bearing at all to instantaneous conditions ... which can change
DRAMATICALLY in a matter of seconds. And, of course, there are indeed
multiple arrival angles at play much of the time anyway.
I have an Elecraft K3 with identical receivers that can be phase locked
for diversity reception. I also have a tribander and 40m yagi on the
same tower spaced about 12 feet apart vertically. One night on 40m I
fed the signal from the tribander into one receiver and the signal from
the 40m yagi into the other receiver ... and then fed the stereo audio
output into my computer sound card with a dual-channel audio
oscilloscope application running. I tuned to a 40m broadcast signal so
that I could get a pure carrier when the announcer was not speaking. I
sync'd the oscilloscope to one signal while observing both on the
screen, and while I couldn't determine the exact phase angles because I
didn't know the electrical lengths to each antenna, I was able to watch
the phase difference in real time (relative phase is retained in the
frequency down conversion to audio). Based upon the 12 foot spacing and
the amount of phase shift I was seeing on the computer screen, I
calculated that the NET arrival angle was changing as much as 20 degrees
within fractions of a second ... which is not unrealistic in light of
other more rigorous studies that have been done by the government over
the past several decades. That net arrival angle could have been due to
a single signal changing in angle or the sum of multiple arrival angles
individually changing in amplitude, but the net result would be the same
to a listener ... perceived fast fading.
HFTA, the terrain analysis program written by N6BV that comes free with
the ARRL Antenna Book, uses the VOACAP arrival angle data for its
optimization algorithm and that's about as good as you're going to get
for planning purposes. For actual real time optimization, you are
pretty much stuck with either using stacked antennas to eliminate
notches or somehow being able to quickly raise/lower your antenna as
On 6/26/2012 3:27 AM, Jukka Klemola wrote:
> Luckily the world is not that simple we really could measure the arrival
> There are often more than one sky wave propagation models happening
> all the time if you are in ZL2.
> > From ZL2, you work a JA, a W6 or anything else that is 'close by' ..
> the propagation usually happens through at least two F2 hops.
> To estimate how the propagation works out, I have used a DOS program
> Miniprop for that purpose.
> W6EL that works in WinXP machines, might have the same feature.
> At least you can set the minimum radiation angle also in W6EL so you
> can experiment by software the phenomena you are after.
> Maybe also VOACP has some possibilities for that, but I found VOACAP
> to be largely inferior comparing to even Miniprop when I was
> experimenting the low angle propagation models for long-haul paths.
> I gave OH6BG a set of feedback, so VOACAP may have been corrected or
> at least improved, I do not know.
> I have been very happy experimenting by software with W6EL and Miniprop.
> ..yes. I still have even DOS computers around so I can use the
> 2012/6/25 Zack Widup<firstname.lastname@example.org>:
>> You would need at least two separate antennas and the ability to
>> measure the phase angle between the signals received by the two
>> On 6/25/12, Rick Kiessig<email@example.com> wrote:
>>> Can anyone suggest a good way to estimate the incoming RF arrival angle for
>>> a given QSO? Are there any software tools to help in that type of analysis?
>>> 73, Rick ZL2HAM
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