Topband: Long Path Direction!

[Eric Scace K3NA]

   I don't think we worked anything on 160m that was "long path" (by which I mean a great circle route of over 20,000 km) while at
3B9C.  I feel pretty certain we did work some skew path, but can't prove it.

   When KA6W was worked we used the NW/SE bi-directional (unterminated) beverage (alias "Eu/NA"), which would imply a long path.
But actually this antenna happened to be used for receiving during the QSO because:

a) the static level on it was much lower than on the NE/SW "JA" bi-directional beverage.  It was our sunset, and the JA beverage
pointed into the darkness and therefore picked up a lot more propagated thunderstorm static than the NW/SE antenna, which was mostly
pointing towards the sunny side of the terminator.  We probably picked up KA6W's signal on some minor lobe or off the side.  The
beverage is about 400 ft long.

b) I was trying each receive antenna and the transmit antenna in turn while tuning around the announced listening frequency.  KA6W
happened to transmit at the time that I was switched over to the NW/SE beverage, and was audible enough for a QSO.  I didn't want to
take the time to try other receiving antennas because the opening time was going to be very brief (few minutes).  KA6W later sent me
a message saying the 3B9C signal was audible for just 2-3 minutes.

   Similarly, when N7UA was worked, I happened to be listening on the other NE/SW beverage... which would be the one more or less in
the direction of a short-path signal.

   Bottom line: there may be reasons other than direction of signal arrival that allow a signal to be better copy on one receiving
antenna rather than another.

-- Eric K3NA

==========

Re: [Fwd: Re: Topband: Long Path Direction!]
from [John Kaufmann] [Permanent Link][Original]

To:  <topband at contesting.com>
Subject:  Re: [Fwd: Re: Topband: Long Path Direction!]
From:  John Kaufmann <john.kaufmann at verizon.net>
Reply-to:  jkaufmann at alum.mit.edu
Date:  Wed, 31 Mar 2004 14:23:04 -0500
List-post:  <mailto:topband at contesting.com>

Ken Brown wrote:

> What is the half power beamwidth of the most directive antenna that any
> of you have for receiving on 160 meters? What about the half power
> beamwidth of the most directive rotatable antenna that you have?
>
> You may know which beverage the signal is strongest on, which may tell
> you approximately which direction it is coming from.


I never give direction of arrival in exact degrees because you are right that
it is not that easy to estimate with any accuracy with the types of directional
antennas most of us use.  For that reason I only refer to directions as NE, E,
SE, etc., which are the orientations of my Beverage antennas.


> But then the exact
> directional pattern of your beverage is unknown. Sure, you can predict
> what it ought to be using modeling programs. I haven't read any
> discussion here about having a helicopter with a signal generator flying
> around several miles from your QTH to measure the actual pattern of your
> antenna, so you don't really know for certain what the pattern is.
>

I have made lots of field strength measurements on directional 160m and 80m
arrays and the results have always coincided closely with theory or modeling
predictions.  I have no reason to doubt that the pattern of a directional
antenna built in close conformity to the models will be reasonably close to the
model, assuming there are no interactions with other objects, etc.

Many of us report very similar results on direction of arrival with Beverage
antennas or vertical arrays, based on assumed theoretical patterns.  If there
were significant pattern deviations from theory, I would not expect to see such
agreement.  The patterns do not need to be perfect of our purposes.  They only
need to be good enough to distinguish differences within the resolution
beamwidth of the antenna.


> So all this discussion about azimuths of incoming signals expressed in
> the precision I see here is rather silly, isn't it? Sure it is fun to
> speculate about which path a signal followed to get to your receiver. I
> think you may be trying to split hairs just a little too thin though.

Knowing the EXACT direction of arrival would be interesting from an scientific
point of view.  However, from a practical point of view, it's really not that
useful to those of us with directional arrays.  The only thing we need to know
is which one of a few possible discrete antenna directions to select and let
nature do the rest.

73, John W1FV

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