§ 2.1515 Spectral measurements.  


Latest version.
  • (a) Set-up. Spectral measurements are to be performed in a shielded room.

    Step (1) Place the EPIRB directly on a metal ground plane, such as the shielded room floor. The EPIRB should be powered by its own internal battery with its standard antenna attached and deployed.

    Step (2) Place a suitable receiving antenna at a convenient distance from the EPIRB and connect it to the input of the spectrum analyzer to observe the radiated signal from the EPIRB. A signal generator and frequency counter capable of operating at 121.5 and 243 MHz are also required for these tests.

    (b) Occupied bandwidth test.

    Step (1) Activate the EPIRB and observe the fundamental frequency on a spectrum analyzer. Adjust location of receiving antenna and spectrum analyzer controls to obtain a suitable signal level (i.e., a level which will not overload the spectrum analyzer, but is far enough above the noise floor to allow determination of whether or not the sidebands are attenuated by at least the amount required in the rules).

    Step (2) Set spectrum analyzer controls as follows:

    I.F. bandwidth: 10 kHz

    Video filter: OFF or as wide as possible

    Scan time: 100 ms./div.

    Amplitude scale: 10 dB/div.

    Scan width: 20 Hz/div.

    Center frequency: 121.5 MHz

    Step (3) Record the signal level in dbm.

    Step (4) Calculate the mean power reference level by adding 10 log10(D), where D is the modulation duty cycle determined in section 2.1513(d) of this part, to the recorded signal level.

    Step (5) Set spectrum analyzer controls as follows:

    I.F. bandwidth: 100 Hz

    Video filter: OFF or as wide as possible

    Scan time: 10 sec./div.

    Amplitude scale: 10 dB/div.

    Scan width: 20 kHz/div.

    Step (6) Check the modulation sidebands for compliance with the required attenuation below the mean power reference level specified in §80.211 of the rules.

    Step (7) Record how the test was performed, instrument settings and the occupied bandwidth in kHz and the 3 dB bandwidth of the carrier in Hz. (See §2.1517 of this part).

    Step (8) Repeat Steps 1 through 7 for the signal at 243 MHz.

    (c) Signal enhancement test. The setup specified in §2.1515(a) is to be used in this method of measuring signal enhancement. Other methods may be used if shown to give results equivalent to or more accurate than this method.

    Step (1) Activate the EPIRB and locate the carrier frequency at 121.5 MHz on the spectrum analyzer. Adjust location of receiving antenna and spectrum analyzer controls to obtain a suitable signal level (i.e., a level which will not overload the analyzer, but is far enough above the noise floor to allow sidebands at least 40 dB below the carrier to be viewed).

    Step (2) Set the spectrum analyzer controls as follows:

    I.F. bandwidth: 10 kHz

    Video filter: OFF or as wide as possible

    Scan time: 100 ms./div.

    Amplitude scale: 5 dB/div.

    Scan width: 10 kHz/div.

    Center frequency: 121.5 MHz

    Step (3) Record the amplitude in dBm.

    Step (4) Calculate the total power output by adding 10 log(D), where D is the modulation duty cycle determined in §2.1513(d) of this part, to the recorded signal level.

    Step (5) Set the spectrum analyzer controls as follows:

    I.F. bandwidth: 60 Hz or less

    Video filter: OFF or as wide as possible

    Scan time: 10 sec./div.

    Amplitude scale: 5 dB/div.

    Scan width: 20 Hz/div.

    Center frequency: 121.5 MHz

    Step (6) Measure and record the carrier power dBm as displayed on the spectrum analyzer.

    Step (7) Calculate the ratio of carrier power to total power from Steps 4 and 6 using the following formula:

    View or download PDF

    dBC= carrier power in step 6

    dBT= total power in step 4

    Step (8) Record instrument settings, sample calculation and the percent of power within ±30 Hz at 121.5 MHz or ±60 Hz at 243 MHz of the carrier frequency.

    Step (9) Repeat the above measurement Steps 1 through 8 for 243 MHz. For the higher frequency, the I.F. bandwidth in step 5 must be 120 Hz or less.

    (d) Carrier frequency test. The setup specified in §2.1515(a) is to be used in measuring the carrier frequency.

    Step (1) Activate the EPIRB and locate the 121.5 MHz signal on the spectrum analyzer. Adjust location of receiving antenna and spectrum analyzer controls to obtain a suitable signal level.

    Step (2) Set the spectrum analyzer controls as follows:

    I.F. bandwidth: 100 Hz

    Video filter: OFF or as wide as possible

    Scan time: 10 sec./div.

    Amplitude scale: 10 dB/div.

    Scan width: 20 Hz/div.

    Center frequency: 121.5 MHz

    Step (3) Combine the output of the signal generator with the EPIRB signal at the input to the spectrum analyzer.

    Step (4) Adjust amplitude and frequency of signal generator output to determine center of carrier frequency component.

    Step (5) Measure signal generator frequency with frequency counter with accuracy of 5 PPM or better and record as carrier frequency.

    Step (6) If applicable, change the type of modulation of the EPIRB and record the shift in carrier frequency as observed on the spectrum analyzer display.

    Step (7) Repeat the above measurement Steps 1 through 6 for 243 MHz.

    [56 FR 11683, Mar. 20, 1991; 60 FR 47302, Sept. 12, 1995]