Topband: Power Coupling in the USA

[Bill Tippett]

NM7M wrote:
>Hence, the insertion loss is very small (about 0.1 dB) to the north.

        Far more significant than power coupling is takeoff angle (TOA)
differences between low dipoles and verticals.  This is what causes
the typical large differences observed of >10 dB depending on path.
Generally low-angle radiators are best for most DX paths in darkness
and high-angle radiators are best for local paths in darkness and
sometimes DX at sunrise.

        At W0ZV I had an elevated GP (20 X 1/4 wl radials 3' above ground) 
and a dipole (apex at 145' and ends at about 100'...not truly a dipole 
but EZNEC said it was closer to a dipole than an inverted-V).  The 
vertical was almost always >10 dB better for DX when in full darkness.  
My dipole was typically >10 dB stronger for local (<300 mi) signals
and for Pacific DX (VK, ZL, YB, etc) at and after my local sunrise 
in Colorado.  The vertical would typically be >10 dB stronger than the
dipole on the same Pacific paths up until sunrise and then the dipole 
would take over.  These effects were due primarily due to takeoff angle 
differences IMHO.

        Remember also that total signal strength is a combination
of many factors including takeoff angle, quality of near and far
field ground conductivity, power coupling, etc.  My guess is that
these are roughly in the order above by the following amounts for NA:

TOA effects:                  >10 dB (low angle vs high angle per EZNEC)
Ground conductivity:            4 dB (VP compared to VG in EZNEC)
Magneto-ionic power coupling:  ~1 dB average (per NM7M's data) 

        While we cannot change our location (far field ground 
conductivity, power coupling effects, etc) we can optimize our antennas 
for low angles and improve our near field ground systems.  Of course 
it's also nice to have a high angle radiator for those occasions when 
that is the best mode (usually local but occasionally for DX).

        Let's not mix apples (takeoff angle effects) and oranges (power
coupling effects) since they are two different issues.  I also would
be interested in any explanations for why TOA's apparently change
from low to high angles at sunrise...but the same is not usually true
for sunset.

                                                73,  Bill  W4ZV