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Command set to read the channel power value

Question asked by jan on Jan 21, 2010
Latest reply on May 17, 2010 by mukta2008
I am working on an automated test environment to test satellite tuner performances.
For calibration, the satellite signal (DVB_S, DVB_S2) signal generator is connected to the E4404B.
By stepping through the frequency range (950MHz .. 2150MHz) with a fixed amplitude (-60dBm), Symbolrate (10MS/s) and modulation ON, the channel powers are measured.
The difference between the selected and the measured value is stored and used to correct the output of the generator when doing the real tuner measurements.
Controlling the E4404B via the GPIB bus seemed simple, but till now I was not successful in getting reliable values.
Many commands like initalisation, setting center frequency(CF), span and some other commands work fine.
The CF is set to the generator frequency, the RBW is manually set to 300kHz, the SPAN to 20MHz, the reference level is set to -65dBm and the average value is calculated over 20 sweeps.
This results in a nice picture with the modulated frequency as a little hill on the noise level.
Reading the channel power can be done by the MEAS:CHP?, READ:CHP? or FETC:CHP? (FETCH) command.
Each one needs its own pre-commands, none for MEAS, some configurations for READ and configurations and INIT to start the measurement followed by FETC to get the measured value.
When using MEAS, the factory values are used for the measurement.
When using READ, all configurationes done like SPAN and RBW should be used, but in my programm the factory values are used again, so there is no difference to MEAS.
When doing configurations followed by INIT:IMM to start the measurement things seem to work, but the FETC command is not recognized.

My question is: What is a good command (command set) on the E4404B to read the channel power value.

Sorry for the long story, but I wanted to describe the situation clearly (at least try to).
If you are familiar with the E4404B and know how to operate it via the GPIB bus by Visual Basic commands, please let me know a solution or a way to get there.