Judging from the variety of responses to this thread, there seems to be far
too much confidence placed in low-cost or free coverage plotting software.
Even the professional-grade programs like ComStudy share the same
limitation: They can estimate coverage area and dead spots based upon input
data, but they are not perfect. You can plug in a digital elevation model
that is supposedly accurate to 30 meters or better, but it is not perfect.
Such models do not include trees, sand dunes, buildings, or similar dips and
peaks that may throw off the calculations. It is a mistake to assume that
the coverage or lack thereof will be perfectly modeled by computer software-
regardless of the computing power.
Even though I own ComStudy 2.2, including the high-resolution digital
elevation models, I still use a BVS "Coyote" instrument to determine actual
coverage. This unit contains modular receivers that are calibrated for
measuring input signal level. The Coyote also contains a GPS receiver for
logging the position and time. A low-power transmitter, usually about one
watt, is placed in continuous operation at the site to be plotted. The
Coyote is put in a vehicle that has a simple omni whip antenna on the roof,
positioned so that the direction of arrival of the test signal has
relatively little effect. The car is then driven around the intended
coverage area, while the Coyote is measuring and recording the received
signal strength and storing same onto a memory card. Later, the data are
processed to create a map showing the signal strength in color along the
routes of travel. Although the Coyote pretty much agreed with the ComStudy
plots, there were many coverage "holes" that appeared in the Coyote data
that were invisible in the ComStudy data. There's not much I can do to
correct such dead spots, other than move the transmitter to a different
site. Moreover, these drive tests often prove that the best coverage is not
always achieved from the highest site in the area.
73, Eric Lemmon WB6FLY
> > Looking for experience and advice in using SPLAT or RM to
"reverse
> > plot" a repeater.
> >
> > What I'd like to do is identify holes in the current coverage
and run
> > a plot with SPLAT or RM with the holes as the center point to
identify
> > potential repeater sites. Do I use mobile parameters (antenna
height)
> > at the hole or do I use an estimated height of 100' assuming
that I'll
> > have a 100' tower at the new site? Restated - how do I insure
that
> > reciprocal results are reliable?
