Re: [Repeater-Builder] Help in using Radio Mobile Deluxe?

Fri, 25 Nov 2005 10:20:24 -0800

The terrain data is out there for free if you know where to look, but it is a pretty big download weighing in at 5GB for the entire US. "SRTM" is the data type that the space shuttle took with a laser of the US in 1996, it has 1 meter resolution and is pretty damn good. and not alot has changed since it was taken.  I was using USGS data before that, but it's accuracy was terrible, at 30m and they measured the stuff back in the 60s using cubits, mercury columns and other cleaver methods of determining height..

But once you have the terrain data RM is damn accurate for the money spent.. If nothing else, send me your data and I will email you the plot.  I need your lattitude and longitude, transmitter power, antenna gain, feedline loss and tower heigt. I use -50 to-100dBmw as my standard scale for ATV work, but you may wish to show -60 to -120 for FM work.

On 11/25/05, Eric Lemmon <[EMAIL PROTECTED]> wrote:
Robert,

Radio Mobile should be used with the realization that an inexpensive (or
free) program cannot possibly duplicate the features and accuracy of
commercial propagation programs like ComStudy, TAP, CovLab, RPS, and
others which are in the $5,000 to $12,000 class.  One of the key elements
in determining coverage is a high-resolution digital elevation model, and
this data is costly, perhaps $500 for a CD covering only a few states.
It's one thing to perform a simple free-space attenuation calculation to
arrive at a raw signal level for some distant point, but the simple
programs can't determine the diffraction and Fresnel losses without
high-resolution terrain data.

One must be careful to avoid the conclusion that "coverage" as found by
any propagation program, whether free, cheap, or expensive, equates to
"repeater coverage."  Regardless of how much signal makes it to some
distant point, the coverage of the repeater will be limited by how well it
receives.  A coverage plot generated by a computer program looks great on
paper, but in reality the coverage of a repeater may be much less than the
plot predicts, especially if the repeater's TX power is far greater than
necessary.

73, Eric Lemmon WB6FLY

georgiaskywarn wrote:

> I joined the above group, posted a question...didn't get a response.
> Going to post again...but thought I might ask here first.
>
> Great program but pretty steep learning curve. Like to "type" with
> someone direct who has used this to figure coverage on their
> repeater.  Not sure if I have all the varibles right.
>
> Don't want to bore the group with my shortcomings on the software...so
> if you could email me direct that would be great.
>
> Thanks,
> Robert
> kd4ydc
> PS Have looked on all the tutorials...not much said on "repeater"
> coverage. txns
>
>
> Yahoo! Groups Links
>
>
>
>







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