[Fwd: Re: Topband: Long Path Direction!]

[John Kaufmann]

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