8525B/8528 Technical Service Manual Adjustments 7-17
Publication No: 15-02036 Issue 6
With the signal generator output set to produce a 1kHz audio output at a
0.5µV PD level switch the noise limiter on and off by shorting TP6 on the
RF Mixer and Dual Synthesizer PCB. When ON, the audio tone should be
clearly heard if the noise limiter is effective.
7.5 Transmitter Performance Checks
7.5.1 Frequency
Check as in section 7.3.10.
7.5.2 Clarifier (when enabled on 8525B-0 only)
Select highest channel frequency on which the clarifier is enabled. Measure
output frequency (Tune pad pressed) at upper and lower clarifier limits for a
range of 0.001% (l0ppm).
7.5.3 ALC
Use the Transceiver Test Unit and Audio Two-tone Source to modulate the
transmitter. Slowly increase the audio input until the output power just
ceases to increase (ALC threshold). Note the PEP output and increase the
audio input by 30dB. The increase in output should be less than 0.5dB.
7.5.4 Power Output and Intermodulation Distortion
8525B/8528
The power output at 2MHz is 100W PEP falling to 90W PEP at 24MHz
(±0.5dB) and the IMD should be better than −26dB as measured on the
spectrum analyser (use 700Hz and 2300Hz Audio Tones).
8528S
Power output at 2MHz is 125W PEP falling to 90W PEP at 24MHz (±1dB);
the IMD should be better than −26dB as measured on the spectrum analyser.
(Use 700Hz and 2300Hz Audio Tones.)
Note: The indication of 100W PEP with two-tone modulation will depend
upon the type of meter used to make the measurement, as follows:
• Peak reading meter: 100W
• RMS reading (thermal): 50W
• Average reading (Bird Model 43): 40.5W
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