abc123 said:
after looking through old HP test and measurement catalog books, here is what I found:
most SA has amplitude accuracy of +-2dB to +-3dB and the SA for EMI measurement has the worst amplitude accuracy. (they are connected to antenna and long cables so usually need to specify attenuation curves to EMI testing software to auto-correct the amplitude when measuring the EMI radiation level, so the accuracy are calibrated for the whole measurement system in testing software),
The power meter with thermistor sensor is the most accurate one, normally you have to switch in between SA and power-meter to get the accurate power measurement.
For most accurate power and frequency measurement the "measuring receiver" is used and they can be used to calibrated the signal generators and attenuators. they are basically the combination of SA and thermocouple power-meter.
Yes you can setting level on signalgenerator with power meter as reference and after 'calibrate' SA from signalgenerator and adjust viewed value with 'offset referense level' (here in hp8594) in SA to same value as generators/power meters view. this calibrate also away loss in cable to SA (if not change this between calibrate and measure).
I see many time people forget/ignore cable loss in measure and 'round' value of external attenuate (ie calculate 30 dB, not real value at 30.8 dB on used frequency) and in the end not understud why measured value not compare to expected and need measure all things again.
'reference offset level' in SA and signal generators is very useful in mathematic way calibrate/compesate for cable loss and extra attenuator so SA (and signalgenerators) always send and view on display 'true' power in ex. dBm on connectors to DUT or rescale to view gain etc.
Suprisely very many, also modern SA (and signalgenerators) have very badly handling of 'offset reference level' with stupids limits as cannot view power higher than ex. +27 dBm in scale (R&S FSH3/6) even if using huge external power attenuator (or external amplifier) and want measure > +50 dBm - is it so idiotic/stupidly I not can belive it.... is a only recalculate of viewed value of power with offset - not more, but both hp/agilent, anritsu and R&S small field SA and signalgenerators cannot do this on right way and many times in the end needs recalculate measured value in head instead (and make possibly to mistakes... ), why, why - is only windows programmers without real RF-measure experience on measure/instrument companys to days???
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If you want calibrate your equipment park with certificate but have (very) small budget, calibrate your power meters in first case (cheap cost compare to calibrate SA) and use this as referense with good signal generator and couple of measured external attenuator (if you not trust accurate on signal generators internal attenuator ladder) to calibrate rest of your equipment , you always need measure and setting offset on generators and SA to compensate cable loss, external attenuators etc. unknow parameters, special in 900 MHz and up.
Simple (cheap or near wear out) 1.5 m measure cable movings or new bending after calibrate can change cable loss value around 1 dB in 900-2400 Mhz... so few dB inaccurate value in SA is a not big problem and in any case always need calibrate/compensate for bigger dB range variation of system loss depend of cable dimensions and length, adapters, attenuators etc.
/Xxargs