Total posts : 45366
Rich is correct regarding the prevailing science and practice for ground systems in shortwave and AM broadcasting. However, if you were to have such an enhanced ground system inspected by the FCC at your Part 15 AM radio station, you should be prepared to supply the technical reasons for operating such a system under Part 15.
The FCC does not define the electrical or mechanical configuration for the buried r-f ground used for Part 15 AM applications. It only states that the lead length used to connect to that buried ground has to be included in the 3-meter maximum radiator length as stated in 15.219(b).
And finally, if you really want the answer to your question, call the nearest District Office of the FCC and ask. They are the folks who will ultimately decide whether you are operating legally or not.
True, and here is a recent e-mail statement from the FCC about the use of elevated Part 15 AM antenna systems. A bit of the header is included to show its authenticity.
From: “Raymond Laforge” Raymond.Laforge @ fcc.gov
To: “Richard Fry”
X-OriginalArrivalTime: 07 Dec 2005 14:17:29.0078 (UTC)
X-pstn-levels: (S:99.90000/99.90000 R:95.9108 P:95.9108 M:94.8923
X-pstn-settings: 5 (2.0000:2.0000) s gt3 gt2 gt1 r p m c
This is a multi-part message in MIME format.
You seek information on the legality of setting these AM transmitting systems on top of billboards and other high, metal structures. Pursuant to 47 CFR 15.219(b), the total length of the transmission line, antenna and ground lead (if used) shall not exceed 3 meters. Thus, we do not except installations on higher structures that result in violation of Section 15.219.