Crown Low Power Transmitters - Crown Broadcast
Crown Low Power Transmitters - Crown Broadcast
Crown Low Power Transmitters - Crown Broadcast
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5.10 Carrier Frequency<br />
Carrier frequency is measured at the output frequency with a frequency monitor<br />
or suitable frequency counter.<br />
To adjust frequency, see section 5.3.3. (FCC tolerance +/– 2000 Hz per FCC Part<br />
73.1540 and 73.1545.)<br />
5.11 Output <strong>Power</strong><br />
The output power reading on the front panel display should be 90–105% of the<br />
actual value. For a more precise measurement, use a watt meter in the RF output<br />
line. See sections 5.4.1 and 5.4.2 for setting power.<br />
5.12 RF Bandwidth and RF Harmonics<br />
You can observe RF bandwidth and spurious emissions with an RF spectrum<br />
analyzer.<br />
In the Stereo mode, feed a 15.0–kHz audio signal into one channel to provide 85%<br />
modulation as indicated on a monitor. Doing so produces 38% main, 38% stereo<br />
subcarrier, and 9% pilot per FCC Part 2.1049. As an alternative, use pink noise<br />
into one channel.<br />
Using a spectrum analyzer, verify the following (per FCC 73.317):<br />
1. Emissions more than 600 kHz from the carrier are at least 43 + 10log(power,<br />
in watts) dB down (58 dB for 30 watts, 63 dB for 100 watts, 67 dB for 250<br />
watts). The scan should include the tenth harmonic.<br />
2. Emissions between 240 kHz and 600 kHz from the carrier are down at least<br />
35 dB.<br />
3. Emissions between 120 kHz and 240 kHz from the carrier are down at least<br />
25 dB.<br />
5.13 Pilot Frequency<br />
The pilot frequency should be within 2 Hz of 19 kHz. (FCC Part 73.322.) Using a<br />
frequency counter, measure 1.9 MHz at pin 1 of U209 on the Stereo Generator<br />
board. A 200–Hz error here corresponds to a 2–Hz error at 19 kHz. If the<br />
frequency is off by more than 50 Hz, you may change the value of C213. (Changing<br />
C213 from 56 pF to 68 pF lowers the 1.9 MHz by about 35 Hz.)<br />
5–8 FM30/FM100/FM250 User's Manual