[sdiy] generators/antennas analogy?

[Josh Landau]

At 11:28 PM 4/22/2001 +0100, you wrote:
>Whilst I am familiar with the idea of 'back emf' in a generator there is
>something I have never understood which Im sure someone can clear up.
>
>I once heard that Radio and TV stations can judge audience figures by the
>amount of power 'absorbed' ie the Watts or MWatts they have to pump out. On
>one level this makes sense. A popular station would need only the weakest of
>transmitters if this were not so. But can the resonance of millions of tuned
>circuits really indicate power usage that accurately? And if not then how do
>they judge audience figures? I don't really buy the argument that grid power
>usage can accurately reflect these things when so many programmes start at
>exactly the same time.

Radio stations judge audience figures in the exact same way as television 
stations and cable stations do - surveys.  In the US, the most common 
rating company is called Arbitron.  It works almost exactly like Nielsen 
ratings.

An outline of their process is found here:
http://www.arbitron.com/radio_stations/home.htm

And transmitter power has nothing whatsoever to do with number of 
listeners.  Transmitter power has to do with area of signal 
coverage.  Higher power, more area covered by a usable signal (usually 
defined as 60 dBu service and 50dBu interfering.)  Each time you double the 
power, you increase the signal at a given location by 3 dBu, I believe.

Realize that some of that last paragraph may be incorrect - I am not a 
licensed radio engineer, I simply work at a radio station.

Josh Landau

Incoming General Manager
DJ - phase 10, the grind
WCBN-FM 88.3, Ann Arbor, MI
http://wcbn.org