Goto Section: 2.1509 | 2.1513 | Table of Contents
FCC 2.1511
Revised as of October 1, 2011
Goto Year:2010 |
2012
§ 2.1511 Measurements of radiated emissions.
The Commission's Rules require that the peak efficetive radiated power
(PERP) of a Class A, B or S EPIRB not be less than 75 mW under certain
specified conditions. The PERP of an EPIRB transmitter is determined by
comparing its level to a reference PERP generated by a standard
quarter-wave monopole antenna located on a one wavelength minimum
diameter metal ground plane. The Rules also require that all spurious
and harmonic emissions be attenuated by a specified amount with respect
to the reference PERP. In addition, there is a limit on the PERP of
radiated emissions with the switch in the test mode. These measurements
are to be made in accordance with the following procedure.
(a) General set-up instructions. Measurements of radiated
electromagnetic emissions (EME) are to be performed on the 30 meter
open field test site described in § 2.1503(a) of this part and on one
of the pair of frequencies listed in § 2.1507 of this part. A receiver,
tuned dipole antennas and a calibrated signal generator as described in
§ 2.1505 of this part are required. The EPIRB should be powered by its
own internal battery with its standard antenna attached and deployed.
(b) Set-up for radiated EME tests.
Step (1) Place a 121.5 MHz quarter-wave vertical antenna element at the
center of the ground plane and connect the output of the calibrated
signal generator to the antenna.
Step (2) Mount the tuned dipole antenna on the antenna mast, tune the
elements to 121.5 MHz and connect the antenna to the receiver.
Step (3) After an appropriate warm up, turn the receiver to the
frequency of the test unit, set the detector to peak mode and the
bandwidth to 100 kHz.
(Note: It is sometimes helpful to monitor the receiver audio output
with a speaker. The EPIRB signal may be identified by its distinctive
modulation.)
(c) Radiated EME tests.
Fundamental emissions-peak effective radiated power
Step (1) Turn on the signal generator and adjust the output to 75 mW at
121.5 MHz.
Step (2) Vary the antenna height from one to four meters in both
vertical and horizontal polarization. Record the highest receiver
reading in dBm as the reference level.
Step (3) Disconnect the signal generator and replace the quarter-wave
vertical element on the ground plane with the EPIRB under test. The
EPIRB is to be positioned directly on the surface of and in the center
of the metal ground plane.
Step (4) Activate the EPIRB.
Step (5) Vary the receive antenna height from one to four meters in
both vertical and horizontal polarization. Record the highest receiver
reading in dBm and the instrument settings, antenna height and
direction for maximum radiation, antenna polarization and conversion
factors, if any, associated with that reading.
Step (6) Repeat Step 5 with the EPIRB switch in the test position.
Return the switch to the normal operation position.
Step (7) Rotate the EPIRB 30 degrees and repeat Steps 5 and 6. Repeat
this step for all successive 30 degrees segments of a full, 360 degree
rotation of the EPIRB.
Step (8) Repeat § 2.1511(b) and Steps 1 through 7 for 243 MHz.
Step (9) Compute the peak effective radiated power for the maximum
level of each measured emission using the following formula:
[MATH: :MATH]
where:
dBm[meas]is the measured receiver reading in dBm, and
dBm[ref]is the reference receiver reading found in step 2 of
§ 2.1511(c).
Step (10) Record the PERP in mW. The FCC limit for minimum power in the
normal operation mode (i.e., with the EPIRB switch in the normal
operating position) is 75 mW. The FCC limit for maximum power in the
test mode is 0.0001 mW.
Spurious emissions
Step (11) Reset the signal generator to operate at 121.5 MHz.
Step (12) For each spurious and harmonic emission to be measured,
retune the receive antenna to the appropriate frequency and repeat
Steps 5 and 7.
Step (13) Determine the FCC limit on power for spurious emissions on
the frequency of each measured emission as follows:
The rules require that spurious emissions be attenuated at least 30
decibels below the transmit power level. Therefore, the maximum
received power limit for a spurious emission can be calculated from the
formula:
dBm[spur]= dBm[meas]+AF[121.5] -AF[spurfreq] -30
where:
dBm[meas]= measured receiver reading (Section 2.1511(c), step 5).
AF[121.5]= tuned dipole antenna factor at 121.5 MHz.
AF[spurfreq]= tuned dipole antenna factor at spurious freq.
Step (14) Record in dB below the fundamental emissions the level of all
spurious and harmonic emissions within 10 dB of the FCC limits.
Goto Section: 2.1509 | 2.1513
Goto Year: 2010 |
2012
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