Fw: Mexican Radio

["Dan Strassberg" <dan.strassberg@att.net>]

----- Original Message -----
From: Dan Strassberg <dan.strassberg@att.net>
To: Garrett Wollman <wollman@khavrinen.lcs.mit.edu>
Sent: Wednesday, May 22, 2002 7:28 AM
Subject: Re: Mexican Radio


> Garrett: No. Over a perfect conductor (for the purposes of this
discussion,
> salt water is close enough), the coverage _radius_ increases as the square
> root of the power, but the coverage _area_ is directly proportional to
power
> (A = Pi r^2). If you hold the antenna efficiency constant, the signal
> strength at any point is directly proportional to the square root of the
> antenna-input power. That relationship is exact. Moreover, over a perfect
> conductor, the signal strength is inversely proportional to the distance
> from the transmitting antenna. For medium-wave signals, it turns out that,
> with typical soil conductivity, you can roughly (really roughly)
approximate
> the ground-wave signal strength at any point as inversely proportional to
> the _square_ of the point's distance from the transmitting antenna. So
> you might say that a 10X increase in power results in a
> _fourth-root-of-10-times_ increase in coverage radius and a
> square-rooot-of-10-times increase in coverage area, but that relationship
> is only a rough approximation, because it depends on frequency and soil
> conductivity. The lower the frequency and the better the soil
conductivity,
> the more inaccurate the approximation. Moreover, because a medium-wave
> station's skywave signal stength allegedly does not depend on the soil
> conductivity in the vicinity of the transmitter site (a point I question),
> the station's _skywave_ coverage area should be directly proportional to
the
> station's power.
>
> --
> Dan Strassberg, dan.strassberg@att.net
> 617-558-4205, eFax 707-215-6367
>
> ----- Original Message -----
> From: Garrett Wollman <wollman@khavrinen.lcs.mit.edu>
> To: Cooper Fox <fox893@yahoo.com>
> Cc: <bri@bostonradio.org>
> Sent: Tuesday, May 21, 2002 5:02 PM
> Subject: Re: Mexican Radio
>
>
> > <<On Tue, 21 May 2002 13:01:30 -0700 (PDT), Cooper Fox
<fox893@yahoo.com>
> said:
> >
> > > Even tho you would have a heck of a power bill...
> > > think of what your broadcast area would be!!??
> >
> > Wouldn't make much of a difference -- do the math.  Even if the level
> > of interference were the same (which it would not be), a tenfold
> > increase in power would give only a threefold increase in coverage
> > area, thanks to the inverse square law.
> >
> > Most of the big European and North African broadcasters are a megawatt
> > or two -- just to get over the noise floor, thanks to all the other
> > European and North African broadcasters running hundreds of kilowatts.
> >
> > -GAWollman
> >
>