14: Maintenance
PRC1099A-MS
14-3
14.2.2
Spectrum Analyzer
Although a spectrum analyzer is not essential for servicing the PRC1099A, it
is useful for testing SSB equipment. The spectrum analyzer operates in the
frequency domain and allows you to observe frequency and amplitude
simultaneously. This is useful for examining the various RF signals for
spectral purity and spurious tones. For example, you can monitor the output
from the phase-locked loop in the transceiver to ensure that the loop is locking
correctly, the phase noise is satisfactory, and that there are no spurious
outputs.
Connect the spectrum analyzer to the transceiver output through an attenuator
to displays harmonics and unwanted spurious outputs.
CAUTION: Do not overload the spectrum analyzer when making
harmonic measurements. If the input level is too high,
the mixer in the spectrum analyzer generates
harmonics internally.
You can also use the spectrum analyzer to measure distortion using a two-tone
test signal—two equal amplitude audio tones in the transmitter audio
passband drive the transmitter to full power output (20W PEP). The distortion
products appear as signals displaced by the separation of the tone frequencies.
Note:
The transmitter PEP is 6 dB higher than the level of each tone in the
two-tone test waveform. If the third order distortion products are 26 dB
below each wanted tone, the intermodulation distortion level is -32 dB
relative to PEP.
Figure 14-1 Power Measurement Waveforms
C W
20W AVG
Two Tone
20W PEP
