Boeing B737 - 121.5 Mhz Frequency; Audio Modulation

B737
MAINTENANCE MANUAL
EFFECTIVITY
Post ELT STC ST03081AT
23-24-00
PAGE 204
JAN 02/07
(b)
Set the Spectrum Analyzer as follows:
1) Center Freq: 121.5 MHz
2) Span: 1 MHz
3) Resolution Bandwidth: 1 MHz
4) Vertical Display: 10dB/Div
5) Sweep: Auto
6) Peak/Avg: Peak
7) Reference Level: 30dBm
8) Time/Div: 20ms
(c) Adjust the reference amplitude to place the peak of the carrier slightly above the top
gratitude line.
(d) Enable the “fine” amplitude adjustment. Set the carrier peak to exactly the yop of the
reference line.
(e)
Read the displayed amplitude.
(f) Repeat for the 243.0 MHz harmonic (Change the “Center Frequency” to 243.0 MHz.
All other settings remain the same).
(g)
The minimum allowed amplitude on 121.5 MHz and 243.0 MHz is 23 dBm (200mW).
(8)
121.5 MHz Frequency
(a)
The ELT transmitter frequency may be measured as follows.
(b)
Connect the frequency counter as shown below:
(c) If the 121.5 MHz carrier frequency is within specified parameters, the 243.0 MHz
frequency will also be within specified parameters.
(d)
The ELT should be within 50 ppm (+/-6.075 KHz) of 121.500000 MHz.
(9)
Audio Modulation
(a)
During the swept tone portions the audio should ”sound” like an ELT.
(b)
Set the unit switch to OFF position.