Topband: dipole height
zr at jeremy.mv.com
Tue Oct 30 19:40:45 EDT 2012
I believe the original query was about transmitting effectiveness which is
where the 15M and 60M heights of the original poster were suggested.
----- Original Message -----
From: "Tom W8JI" <w8ji at w8ji.com>
To: "'topband'" <topband at 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
> 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.
> Topband reflector - topband at contesting.com
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