Sec.  2.1503   Test environment.

   (a) Measurement sites. Radiated emission tests for peak effective radiated
   power (PERP), spurious emissions and power in the test mode are to be
   performed on an open field test site as shown in Figure 1. The site is to be
   located on level ground with an obstruction-free, 60 m by 52 m, elliptical
   area. The site is to be equipped with an antenna mast capable of adjustment
   from 1 to 4 m. The center of a metal ground plane at least one wavelength in
   diameter at 121.5 MHz (2.47 m) is to be located 30 m from the receiving
   antenna. The ground plane is to have provisions for mounting removable
   quarter-wave verticle elements to produce a monopole antenna at both 121.5
   and 243 MHz with the VSWR of less than 1.5.

   Note: It is desirable that the level of radiated ambient EME at the test
   site be at least 6 dB below the FCC limits applicable to the EPIRB. It is,
   of course, not always possible to meet this condition. If the ambient field
   strength at some frequencies within the specified measurement ranges is too
   high, it is recommended that one or more of the following corrective steps
   be employed:

   (1) Perform measurements in critical frequency bands during hours when
   broadcast and other radio stations are off-the-air and ambients from
   industrial equipment are lower.

   (2) Insofar as is possible, orient the axis of an open area test site to
   discriminate against strong ambient signals.

   (3) Vary the bandwidth of the measuring instrument to separate ambient EME
   from emissions from the EPIRB.

   (b) Temperature. Except as otherwise noted, the ambient temperature during
   testing is to be within the range of 4 to 35  °C (40 to 95  °F).