[BC] uPFM (Micro-Power FM)

[WFIFeng@aol.com]

In a message dated 07/21/2006 07:26:27 AM Eastern Daylight Time, 
rfry at adams.net writes:

> Coverage can be better than that, actually.  The link below shows the 
>  calculated fields for several values of low ERP. The legal Part 15 FM 
>  system is plotted in red, and has a field between 2 and  3 ?V/m at 300 
>  meters (~984 feet).
>
>  http://i62.photobucket.com/albums/h85/rfry-100/6417f684.gif
>  
>  That's probably about the limit even with a clear path, a good receiver, 
>  and a good receive antenna.

How many typical, consumer-grade, FM radios have sensitivity even 
*approaching* 2-3 uv, though? How many areas of the US have frequencies that are clear 
enough to even permit reception at that level, providing the receiver is capable 
of it? Not many, I'm sure... and of those that did, the residences would be 
spread out too far to reach more than maybe 4, if you could put the tx right in 
the middle of the intersection of the 4 property lines!

In the real world, with real interference & real radios with whip antennae, 
the actual limits of those nanowatts into a 1/2 wave dipole would barely cover 
a single acre. In a dense suburban setting, that would be maybe 1/2 a block, 
with perhaps a few dozen potential residences with a useful signal. Forget 
major urban areas, there just wouldn't be enough "clear" frequencies to put the tx.

It would be nice if the actual P15 limit for FM *could* be raised to 25 
milliwatts. That would provide *useful* coverage of at least a few blocks, figuring 
on 1 or 2 mv, using your graph. (Thanks for posting it.) Then, someone could 
manufacture a genuine FCC approved transmitter (Think: FM Rangemaster) for it. 
They'd sell a good number of them, I'm sure.

Willie...