[BC] Part 15 radio station

[Richard Fry]

Dana Puopolo wrote:
>I'd also mount the transmitter on the roof, with a 25 foot 3/4 inch copper 
>pipe coming down the side of the building and connected to a couple of 
>ground rods and/or the cast iron water pipe coming into the building (the 
>FCC allows for safety grounds in part 15 installations).
_____________

Installing a Part 15 AM system with a long, conducting path to a 
"lightning" ground has lead to FCC problems for some (see FCC link below). 
In reality the long ground conductor will radiate considerably more than 
the 3-meter conductor considered to be the antenna.  FCC Part 15.219(b) 
limits the total length of a Part 15 AM antenna and ground lead to 3 
meters.

Some Part 15 AM operators have defined the ground lead as only the short 
conductor connecting the transmitter chassis to another conductor, such as 
a flagpole, tower, "massive ground wire," billboard steel etc.  But this is 
just semantics -- the r-f current in the short "ground lead" continues 
along the length of whatever conductor it connects to until it reaches a 
true r-f ground (something buried in the earth).  That current produces 
radiation.

The second link below leads to a calculation of the coverage of a 
better-than-typical Part 15 AM system when its antenna and ground path are 
limited to 3 meters, total.  The 2 mV/m groundwave field strength radius of 
this setup is barely more than 200 feet, in open terrain.  Urban conditions 
would reduce that.

Evidently the FCC does not intend for Part 15 systems to be very useful for 
"broadcast" purposes.

http://www.fcc.gov/eb/FieldNotices/2003/DOC-269883A1.html .

http://i62.photobucket.com/albums/h85/rfry-100/Part_15_AM_Calc_2.gif

RF