SOUTHERN AVIONICS COMPANY
SE Series Installation and Setup
7-9
Operational Checks
7.10.2
Scope the modulation waveform and record the max/min envelope values to calculate the
modulation percentage. (vmax-vmin)/(vmax+vmin)=mod%
7.10.3
Verify that the set modulation percentage and the calculated modulation percentage agree to within
5%.
7.11 Transmitter #2 Frequency Checks
7.11.1
As an example, when calibrating RF output frequency, Federal Aviation Administration (FAA)
regulations state that a maximum variance of + 100 parts per million (ppm) Hertz is allowed
provided output power is less than 200 Watts. The user must check with local authorities to
determine the actual allowed limits.
The formula for calculating the variance is:
variance = (operating frequency * 100) / 1,000,000
For example, at 320,000 kHz the variance allowed would be 32 Hz.
7.11.2
Connect a calibrated frequency counter to the dummy load to measure the RF output frequency.
7.11.3
Verify that the measured frequency equals the site frequency ± 100 ppm Hz. If the frequency is
within this tolerance, disconnect the frequency counter.
7.12 Transmitter #2 Morse Code Identifier Check
7.12.1
Attach the oscilloscope to the dummy load and verify that the output RF modulation envelope is
being keyed with the site’s required Morse code identifier entered earlier in this section.
