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Loss-of-lock fault maintenance method for spectrum analyzer maintenance

Time：2021-04-25                1320

In addition to the common start-up display failure, there is also a major failure of the spectrum analyzer to lose lock.
Loss of lock is usually manifested in that the signal frequency deviates from the set position, or the signal cannot be seen or carries a significant large-scale spurious signal. Due to the complexity of the local oscillator circuit of the spectrum analyzer, it involves circuits and microwave components such as reference ring board, frequency synthesis board, microwave driver board, narrow-band intermediate frequency board, YTO, local oscillator frequency doubling amplifying component, directional coupler, etc. It must first be confirmed which circuit unit is faulty.
Analysis process: The local oscillator signal source of the spectrum analyzer is developed from free oscillation to frequency synthesis. Therefore, first input 2GHz and 6GHz signals respectively. If the lock is lost at 2GHz and the lock is not lost at 6GHz, it means that the first local oscillator is normal and the second The local oscillator is out of lock; if both frequencies are out of lock, it may be that the first local oscillator is out of lock or the first and second local oscillators are out of lock. The schematic diagram is as follows:

(1) To judge whether the first local oscillator is out of lock, check according to the "first local oscillator preset". If it is not normal, follow the inspection steps in the debugging of the first local oscillator preset. If it is normal, go to the next step.
(2) To judge whether the second LO is out of lock, check according to the "Second LO Preset". If it is not normal, follow the inspection steps in the second LO preset debugging. If it is normal, go to the next step.
(3) Determine whether the 300MHz third local oscillator is normal. If this local oscillator loses lock, it is actually the 100MHz crystal oscillator that is abnormally locked. At this time, measure the external 100MHz. If the signal jitter is abnormal at this time, it may be that the 100MHz crystal oscillator is out of lock.
(4) Determine whether the 28.9MHz fourth local oscillator is normal. This oscillator is a crystal oscillator. If it loses lock, it may deviate from the century frequency point by about 20kHz. The bandwidth of the spectrum analyzer should be set small enough, about 100kHz to be able to observe arrive. The above knowledge about spectrum analyzer maintenance is organized and released by Xi'an Agitek Instrument Maintenance Center Network (www.ywkjt.com). Welcome to leave a message for discussion.