I believe the original query was about transmitting effectiveness which is
where the 15M and 60M heights of the original poster were suggested.
Carl
KM1H
----- Original Message -----
From: "Tom W8JI" <w8ji@w8ji.com>
To: "'topband'" <topband@contesting.com>
Sent: Tuesday, October 30, 2012 7:18 PM
Subject: Re: Topband: dipole height
RDF is the key point to improve signal noise, not gain. Vertical or low
dipole has very or none directivity, so low RDF or directivity does not
improve signal noise.
In general, this is the case, but it is not always true.
Since I started using RDF, let me explain what it really is.
RDF is really just directivity. I used RDF so people would stop using
gain, because gain has little value for receiving. For example, if I place
two Beverages side-by-side 1/4 wave apart there is almost no pattern
change. Gain increases 3 dB, but certainly not receiving ability!!!
As long as the noise is evenly distributed in all directions, or if
dominate noise would be randomly distributed in all directions at
different times, RDF works great as a guideline.
If dominant noise comes from the SAME direction and polarization as the
desired signal, nothing will help. Anything that nulls the noise also
nulls the signal.
If dominant noise comes from a null direction, the difference between gain
in the desired signal direction to null of the noise will set the
performance. For example, with a thunderstorm off the rear, F/R is most
important.
If noise is unevenly distributed, then it becomes very complex.
Most people out in a rural area are probably in a situation where whatever
QRM or noise bothers them, comes from random, differing, directions. Some
people in congested areas have significant noise from one direction, and
they need a deeper null in that specific direction. Going for
exceptionally high F/R is meaningless unless there is somewhat-consistent
strong QRM from the rear.
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