[ARDF] maps

[Jay Hennigan]

Mike (KA5CVH) Urich wrote:

> The rules actually require that you use an antenna that radiates
> poorly in all directions and planes so that directionality and
> polarization is not an issue.

This isn't exactly correct.  If by "poorly" you mean "with little gain", 
then the statement has some merit.  Antennas achieve gain by 
concentrating the signal in the desired direction.  Even omnidirectional 
antennas such as collinears do this by concentrating energy at the horizon.

Variations in strength of the transmitted signal should not be a factor 
in ARDF.  As the antennas are temporary installations, it is rarely 
possible to make them exactly vertical.  It is also often difficult to 
make them strong enough that they won't sway in the wind.  Therefore 
gain antennas that concentrate energy at the horizon can be a problem. 
Crossed dipoles or halo antennas are a good compromise as they are 
nearly omnidirectional horizontally and the vertical pattern is broad 
enough that slight misalignment or swaying in the wind won't be a factor.

Polarization is a horse of a different color, especially on 2 meters. 
Most yagi antennas have a tighter pattern horizontally than vertically, 
thus the specification that the transmitter be horizontally polarized.

In addition, hunters can get clues as to the reliability of a bearing by 
observing the behavior cross-polarized.  A direct signal will drop in 
strength noticeably when the receiving antenna is cross-polarized. 
Reflections tend to randomize polarization.  The dip in signal strength 
from turning the receiving antenna cross-polarized will be less or the 
strength may even go up when hunting a reflection.

So, polarization is indeed important.  Horizontal is preferred for 
serious competition.  But at least make all of the antennas the same and 
place them at the same height.  If all you have are ground planes or 
vertical antennas and you're anxious to get some activity going, go for 
it!  Heck, if all you have are rubber duckies and you can get some 
activity do that too.  Just make them all the same and tell the hunters 
what the polarization will be on the hunt.  Once you have a pack of 
hounds and some spirit going, the fancy maps and antennas can come next.

--
Jay Hennigan - CCIE #7880 - Network Engineering - jay at impulse.net
Impulse Internet Service  -  http://www.impulse.net/
Your local telephone and internet company - 805 884-6323 - WB6RDV