standards and guidelines for communication sites - Radio And ...

ENGINEERING CONSIDERATIONS APPENDIX A: ELECTROMAGNETIC ENERGY INFORMATION
A.3.7 UPTIME
11.D-8
14.D-9
17.D-10
21.D-11
12.C-8 C 15.C-9 18.C-10 22.C-11 24.C-12
13.B-8 16.B-9 19.B-10 23.B-11 25.B-12
FIGURE A-10 COMPOSITE RF FIELDS WITH FIVE ANTENNAS TRANSMITTING
The combined fields produce levels exceeding the MPE allowed in all areas surrounding the antennas.
In these situations, some means of controlling exposure must be used. These techniques may include RF
protective clothing, re-engineering the antenna system, or power shutdown or reduction when working
in the area. While power shutdown or reduction may appear to be an effective technique, either may be
impractical for wireless communications services. It is normally reserved for broadcast transmitters.
One preferred method of addressing this is to elevate the antennas above the roof area.
Complex antenna sites have a “personality” that makes them unique. The personality of the site is not
only determined by the RF power, frequency, and manufacturer of the equipment, but by the operational
characteristics. The RF level and frequency can be determined by understanding the equipment
specifications, but operational characteristics can only be quantified by monitoring the usage. Because
of the high number of pagers, paging transmitters will have a very high transmitter duty cycle. Trunking
(SMR) transmitter activity will depend on customer loading density. This can range from transmitters
rarely transmitting, to transmitters rarely not transmitting. Private customer equipment will have a very
diverse usage characteristic that can not be predicted. The important point in understanding the
characteristics of different services is that they can seldom be predicted.
Additionally, characteristics for transmitters will change due to cultural elements. Transmitters located
in Las Vegas will have considerably different uptime characteristics than transmitters located in San
Antonio, Texas or New York City. Tests have shown that a site will vary significantly from one time
period to another. Sample measurements on a roof of a large building showed a variation in transmitter
activity of over 30% between 11:00 a.m. and 2:00 p.m.
Uptime relates to all of the transmitter activity of a site. Uptime can seldom be predicted or
characterized precisely, and thus usually must be measured. The amount of Uptime directly affects the
EME exposure levels on a site.
A-18 68P81089E50-B 9/1/05
27.D-13
28.C-113
29. B-13