Analysis of calibration procedures and precautions for Keysight spectrum analyzers

Aetna Testing/Keysight is the brand leader. In the early days, it was called Hewlett-Packard/HP. Around 2000, after the separation of civilian products and testing, it was changed to Agilent/Agilent (electrical, medical, chemical analysis). At the end of 2014, the name of electronics was changed to Keysight Technologies. Of course, the Keysight series of electrical measuring instruments are not cheap, ranging from tens of thousands to hundreds of thousands of precision instruments; therefore, it is necessary to use them according to the correct process and calibrate the instruments regularly. So what are the issues that need to be paid attention to during the calibration process of Keysight series instruments?

1. Calibration procedure of spectrum analyzer

The internal computer of the instrument has three common calibration procedures: frequency calibration, amplitude calibration and preselector (YTF) calibration.

1. Frequency calibration

When the spectrum analyzer undergoes vibration, transportation, long-term storage, or large environmental temperature changes, the frequency tuning of the spectrum analyzer will change, causing frequency measurement errors. In severe cases, the measurement signal will shake left and right. This can be eliminated through frequency calibration. Phenomenon. The calibration process mainly uses the 300MHz signal as the reference signal to perform error calibration on the spectrum analyzer's scanning time, center frequency, span (span), YIG main coil delay, secondary coil sensitivity, and frequency sweep sensitivity, so as to make the frequency tuning range of the spectrum analyzer normal.

Calibration method

Use the frequency/amplitude calibration cable to connect the calibration signal (CAL OUTPUT) to the signal input of the spectrum analyzer. Press [CAL] [CALFREQ], the spectrum analyzer enters the frequency calibration procedure. After the calibration is completed, the "CALDONE" message appears on the screen. Press the [CALSTORE] key to store the calibration data in the E2PROM of the instrument.

2. Amplitude calibration

Like frequency calibration, when the measurement amplitude accuracy of the spectrum analyzer changes, the instrument can meet the factory specifications through the amplitude calibration procedure. The process mainly uses the 300MHz signal as the reference signal to adjust the entire channel amplitude of the spectrum analyzer, resolution bandwidth filter, Measure and correct errors in the logarithmic amplifier and input attenuator amplitudes.

Calibration method

Use the frequency/amplitude calibration cable to connect the calibration signal (CAL OUTPUT) to the signal input of the spectrum analyzer. Press [CAL] [CALAMP], the spectrum analyzer enters the amplitude calibration procedure. After the calibration is completed, the "CALDONE" message appears on the screen. Press the [CALSTORE] key to store the calibration data in the E2PROM of the instrument.

3. Preselector (YTF) calibration

The sweep and tracking of the preselector is key to the harmonic band of the spectrum analyzer. The machine is designed with a drive circuit that is independent of the first local oscillator, calibrating and driving each band separately. During fast sweep, slow sweep and cross-band sweep of the spectrum analyzer, the hysteresis and delay of the first oscillator and preselector are compensated, which greatly improves the tracking characteristics of YTF. If the spectrum analyzer has an amplitude error of 5dB or more in the harmonic band, it is often caused by the instrument being placed for a long time and the ambient temperature changing greatly. A poor pre-selected tracker will cause amplitude measurement errors or even no signal. In this case, YTF calibration should be performed.

Calibration method

Use a YTF calibration cable to connect the 100MHz comb wave (COMB) signal to the RF input of the spectrum analyzer. Press [CAL] [CALYTF], the spectrum analyzer enters the YTF calibration procedure. After the calibration is completed, the "CALDONE" message appears on the screen. Press the [CALSTORE] key to store the calibration data in the E2PROM of the instrument.

If an error signal occurs when exiting during calibration or the calibration cannot be completed, press [CALFETCH] to retrieve the calibration data. At this time the instrument will need to be readjusted and repaired.

2. Calibration data after calibration of the spectrum analyzer

The HP859X series spectrum analyzer can not only calibrate various indicators of the instrument, but also store various calibration data in the memory for reference by operation and maintenance personnel. As long as you enter the maintenance menu, the calibration data can be displayed.

Specific steps

Press menu [CAL] (MORE) (MORE) (SERVICEDIAG) (DISPLAYCALDATA), then the amplitude calibration table of the spectrum analyzer will be displayed on the screen.

The table contains the amplitude error correction values ​​for each level of the input attenuator (RFATN) with an attenuation of 0 to 70dB in 10dB steps, and the amplitude error of each level of the logarithmic amplifier (LOG) with an amplification of 0 to 50dB in 10dB steps. Correction value, the linear amplifier (LIN) amplification amount is 10~40dBm, the amplitude error correction value of each gear in 10dB steps, the resolution bandwidth amplifier (BWAMP), the amplitude error of each gear in steps of 1, 3, 10, Correction value; correction value of the entire channel gain (GAIN) of the spectrum analyzer. The gain correction value is expressed in the form of DAC. The minimum correction value is 0, the maximum is 255, etc.

Through the amplitude calibration table, we can not only analyze the performance indicators of each hardware circuit in the spectrum analyzer, but also bring certain convenience to the maintenance of the instrument. The maximum amplitude correction capability of the internal computer of the spectrum analyzer is ±2.2dBm, and the maximum correction value of the DAC is 255. If the spectrum analyzer performs amplitude calibration, and various error correction values ​​exceed ±2.2dBm, the maximum correction value of the DAC is 255. , the calibration cannot be completed and an error message will appear on the spectrum analyzer screen.