Topband: dipole height

[Tom W8JI]

>> 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.