National Instruments PXI-6683 Series User Manual

Also see for PXI-6683 Series: Installation guide User manual

Contents

surface is typically -130 dBm. Targeting a signal strength of -125 dBm at the SMB input, youcan compute the maximum cable length as:Max_cable_loss = -130 dBm + antenna_gain - (-125 dBm)Max_cable_length = Max_cable_loss / (loss_per_unit_of_distance)For example, if you use an active antenna with gain of 28 dB and RG-58 cable, which has arated loss at 1.5 GHz of about 0.8 dB/m (24.5 dB/100 ft), the maximum cable length youcould use is:Max_cable_loss = -130 dBm + 28 DB - (-125 dBm) = 23 dBMax_cable_length = 23 dB / (.08 dB/m) ≈ 29 mNote The GPS antenna kit offered by National Instruments comes with a 30 mcable, which has a loss of 15 dB/100 ft, making the total loss in the cableapproximately 14.8 dB.CalibrationThis section discusses the calibration of the PXI-6683 and PXI-6683H.Calibration consists of verifying the measurement accuracy of a device and correcting for anymeasurement error. The PXI-6683 Series are factory calibrated before shipment atapproximately 25 °C to the levels indicated in the Specifications. The associated calibrationconstants—the corrections that were needed to meet specifications—are stored in the onboardnonvolatile memory (EEPROM). The driver software uses these stored values.Factory CalibrationAll PXI-6683 Series boards go through factory calibration. During that process the TCXOfrequency is adjusted so that it matches a reference 10 MHz atomic clock. A calibrationconstant is then stored in on-board, non-olvatile memory, along with other calibrationmetadata, such as calibration date and temperature.The calibration constant is used at start-up when the board is configured for free runningmode. When the PXI-6683 Series module is configured to use GPS, IEEE 1588, IEEE802.1AS, IRIG-B, or PPS as its time reference, the TCXO frequency is adjusted according tothe time reference, and the calibration constant is no longer used. If the board returns to freerunning mode, because it was so configured or the time reference is no longer present, then thelast applied TCXO voltage is retained (it does not revert to the calibration constant).Note If the board is configured to use IEEE 1588 as the time reference and isselected as the 1588 master with 1588's BMCA, the device will be free running anduse its calibration constant.Additional InformationRefer to ni.com/calibration for additional information on NI calibration services.28 | ni.com | PXI-6683(H) User Manual

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