What are the calibration procedures for spectrum analyzers?

The biggest feature of the HP859X series spectrum analyzers is that they use their powerful software functions to make up for the shortcomings of their hardware design, which not only reduces hardware design, but also reduces the hardware debugging process.

Spectrum Analyzer Calibration Procedure

The instrument's internal computer has three commonly used calibration procedures: frequency calibration, amplitude calibration and preselector (YTF) calibration.

1. Frequency calibration

When the spectrum analyzer is vibrated, transported, placed for a long time or has a large ambient temperature change, the frequency tuning of the spectrum analyzer will change, resulting in frequency measurement errors. In severe cases, the measurement signal will shake left and right. This phenomenon can be eliminated through frequency calibration. The calibration process mainly uses the 300MHz signal as the reference signal to calibrate the error of the spectrum analyzer's scanning time, center frequency, span (span width), YIG main coil delay, secondary coil sensitivity, and sweep sensitivity, so that the frequency tuning range of the spectrum analyzer is normal.

The calibration method is: use the frequency/amplitude calibration cable to connect the calibration signal (CALOUTPUT) to the signal input terminal of the spectrum analyzer. Press [CAL]〔CALFREQ〕, and 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

Similar to frequency calibration, when the spectrum analyzer's amplitude measurement accuracy changes, the amplitude calibration procedure can be used to make the instrument meet factory specifications. The process mainly uses the 300MHz signal as the reference signal to measure and correct the errors of the spectrum analyzer's entire channel amplitude, resolution bandwidth filter, logarithmic amplifier, and input attenuator.

The calibration method is: use the frequency/amplitude calibration cable to connect the calibration signal (CALOUTPUT) to the signal input terminal of the spectrum analyzer. Press [CAL]〔CALAMP〕, and 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 are the key to the harmonic band of the spectrum analyzer. The design of this machine adopts a driving circuit that is independent of the first local oscillator, and calibrates and drives each band separately. When the spectrum analyzer is fast-sweeping, slow-sweeping, and cross-band sweeping, the hysteresis and delay of the first oscillator and the preselector are compensated, which greatly improves the tracking characteristics of the YTF. If the spectrum analyzer has an amplitude error of 5dB or more in the harmonic band, it is often caused by the long placement of the instrument and large changes in ambient temperature. A poor preselector tracker will cause amplitude measurement errors, or even fail to measure the signal. At this time, YTF calibration should be performed.

The calibration method is: use the YTF calibration cable to connect the 100MHz comb wave (COMB) signal to the RF input of the spectrum analyzer. Press [CAL]〔CALYTF〕, and 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 instrument's E2PROM.

If you exit during calibration or calibration cannot be completed and an error message appears, press [CALFETCH] to retrieve the calibration data. The instrument will then need to be readjusted and repaired.