8525B/8528 Technical Service Manual Adjustments 7-5
Publication No: 15-02036 Issue 6
7.3 Preset Adjustments
7.3.1 Test Equipment Required
• A calibrated CRO with 10X probe with 10MΩ and less than 12pF input
impedance. Y amplifier frequency response of at least 25MHz.
• RF dummy load, 50Ω 100W RMS minimum and Power Meter to suit.
• RF signal generator covering the range 250kHz to 30MHz and capable
of providing calibrated signals down to 0.25µV EMF from a 50Ω
source.
• Frequency counter capable of resolving to 1Hz frequencies up to
24MHz.
• Regulated Power Supply which can be set to 13.6V ±0.2V and capable
of supplying 20A peak current.
• Two-tone (i.e. 700Hz and 2300HZ) audio generator capable of
providing 0–l00mV RMS.
• Spectrum analyser suitable for SSB
• Multimeter or meters for measuring voltages (20kΩ/V or better) and
current (l00mA and 1A ranges) and an audio voltmeter.
• Transceiver Test Unit to Codan drawing 04-01868. (The isolating
transformer should be screened to prevent pick-up from nearby mains
transformers.)
• Square-wave generator capable of 5.5V pp at 100Hz.
• Decade resistance box for ease of determining select-on-test (SOT)
resistors. (A resistance box constructed using the E12 series values of
resistors is very useful.)
Before making any adjustments, the supply voltage must be set to 13.6V
±0.2V.
When working on the low level stages, e.g. the receiver and exciter, the PA
may be isolated by removing the dual coax socket to the PA and Filter PCB.
This will prevent unnecessary heating of the heatsink and removes the
possibility of high level RF fields being picked up by test leads which may
cause erroneous measurements or transmitter instability. Note that this also
disconnects the receive path (between the PA and Filter PCB and RF Mixer
and Synthesizer PCB).
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