[BC] Re: TIS Facilities

[Richard Fry]

Quoting FCC 90.242 concerning TIS stations:

"(4) For a station employing a conventional radiating antenna(s) (ex.
vertical monopole, directional array) the following restrictions apply:
(i) The antenna height above ground level shall not exceed 15.0 meters 
(49.2
feet).
(ii) Only vertical polarization of antennas shall be permitted.
(iii) Transmitter RF output power shall not exceed 10 watts to enable the
user to comply with the specified field strength limit.
(iv) The field strength of the emission on the operating frequency shall 
not
exceed 2 mV/m when measured with a standard field strength meter at a
distance of 1.50 km (0.93 miles) from the transmitting antenna system."

Does anybody know why the FCC would define the effective length (height) of 
a TIS radiating structure plus the maximum output power of a TIS 
transmitter when they also define the maximum permissible TIS field 
strength at 1.5 km?

Why should the FCC care what combination of TPO and antenna system 
height/efficiency might be needed to produce that defined field strength 
value for the terrain conductivity conditions and the operating frequency? 
They don't define either of those for Part 15 "Campus" setups -- only that 
a certain field strength value cannnot be exceeded at a certain distance 
beyond the campus perimeter.

Likewise with Part 15 operations in the FM broadcast band, where nothing is 
stated about TPO or antenna efficiency/gain.  The limit applied to these 
systems is placed on the peak field strength they produce 3 meters away 
from their radiators.

Why this difference for TIS stations?

RF