02 - LabSat Operation
Depending on model type, the LabSat is able to record RF data directly from an active antenna and store the data on a hard drive or generate GNSS RF signals from data stored on a hard drive.
There are two RF ports on the LabSat these are marked ANTENNA and RF OUT. The ANTENNA socket is used to connect an active GPS antenna when recording data. During recording, the RF OUTPUT port is switched off to ensure that it does not interfere with the recorded data.
The RF IN socket is used to connect an active GNSS antenna when recording data. During recording, the RF OUT port is switched off to ensure that it does not interfere with the recorded data.
The RF OUTPUT port is used to connect the LabSat to the GPS system under test. The output signal of the LabSat is at a nominal level of -85dBm when replaying previously recorded data. Using the PC software, it is possible to attenuate the LabSat output by up to 30dBm giving a signal power range of -85dBm down to -115dBm. Adjustment to the output attenuation is made using the slider control in the LabSat software. With the slider at the lowest position on the screen, attenuation is 0dB meaning 0dB of attenuation on the nominal -85dB output. As the slider is moved along, the attenuation increases, reducing the output level accordingly.
When replaying RF data into a GNSS engine, it may be necessary to increase attenuation in order for the GNSS engine to acquire satellite data.
It is also important to note when replaying previously recorded GPS/Galileo data, that it may be required to cold start the GNSS engine under test. This is because GNSS engines rely on downloaded almanac data to determine which satellites to look for at a given date and time. A cold start of the GNSS engine should clear any stored almanac data, forcing the GNSS engine to look for all satellites available.