5.10 Carrier Frequency
Carrier frequency is measured at the output frequency with a frequency monitor or suitable
frequency counter.
To adjust frequency, see section 5.3.3. (FCC tolerance +/– 2000 Hz per FCC Part 73.1540
and 73.1545.)
5.11 Output Power
The output power reading on the front panel display should be 90–105% of the actual value.
For a more precise measurement, use a watt meter in the RF output line. See sections
5.4.1 and 5.4.2 for setting power.
5.12 RF Bandwidth and RF Harmonics
You can observe RF bandwidth and spurious emissions with an RF spectrum analyzer.
In the Stereo mode, feed a 15.0–kHz audio signal into one channel to provide 85% modula-
tion as indicated on a monitor. Doing so produces 38% main, 38% stereo subcarrier, and
9% pilot per FCC Part 2.1049. As an alternative, use pink noise into one channel.
Using a spectrum analyzer, verify the following (per FCC 73.317):
1. Emissions more than 600 kHz from the carrier are at least 43 + 10log (power, in watts)
dB down (71 dB for 600 watts). The scan should include the tenth harmonic.
2. Emissions between 240 kHz and 600 kHz from the carrier are down at least 35 dB.
3. Emissions between 120 kHz and 240 kHz from the carrier are down at least 25 dB.
5.13 Pilot Frequency
The pilot frequency should be within 2 Hz of 19 kHz. (FCC Part 73.322.) Using a frequency
counter, measure 1.9 MHz at pin 13 of U208 on the Audio Processor/Stereo Generator
board. A 200–Hz error here corresponds to a 2–Hz error at 19 kHz. If the frequency is off
by more than 50 Hz, you may change the value of C213. (Changing C213 from 56 pF to 68
pF lowers the 1.9 MHz by about 35 Hz.)
5.14 Audio Frequency Response
For the response tests, take the readings from an FM modulation monitor.
Make audio frequency response measurements for left and right channels at frequencies of
50 Hz, 100 Hz, 400 Hz, 1 kHz, 5 kHz, 10 kHz, and 15 kHz. See sections 5.9.1 and 5.9.2.
5-8 FM600 User’s Manual
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