From here, the output amplitudes of the phase generator unit were measured and then adjusted so that the signal level at each output was within +/- 1 dB of the desired signal level of 7 dBm. Here this error is driven by the precision of readily available attenuators. In the end, a few attenuator value needed to be change as well as some small adjustments to the DC power cables and connectors to a few units in order to get the gain of that unit to stay stable. After the calibration, all of the outputs were measured to be within the desired tolerance. The results were also noticed in the higher number transmitters putting out a tad bit more power than prior to the recalibration.
During this trip, a few more timing questions would be answered following the Nov. 29, 2012 trip. The figure to the left shows control signals being used at the Blackstone radar. The magenta trace is the scope sync signal; the green trace is the T/R signal; the yellow signal is an RF pulse that is supposed to go to a transmitter. The RF pulse shows where the TX On signal occurs since a switch in the radar control electronics driven by the TX On signal produces the source for this RF pulse. By looking closely, the scope sync signal cane be measured to be going high about 1 millisecond before the TX On signal goes low (here the TX On is the inverse of the RF pulse amplitude). The T/R signal is as expected and goes high about 60 microseconds before the RF pulse. The scope sync signal goes low before the T/R signal but also at the same time that the RF pulse stops. This falling edge of the scope sync signal acts as a trigger for the digital receiver card to mark the time when the radar should start receiving. However, since we don't record the first 180 km worth of data, some early samples are thrown out in data processing. NOTE: The green trace's scale should be 5 V per division instead of 50 V.
With the short remaining time, a stab at the time difference measurement was attempted using a method similar to measurements performed by the University of Alaska crew during the installation of MSI radars. However, because the receiver front end at the Blackstone site is configured differently than the MSI radars, this method of measurement could not be completed.
Before leaving the site, it was observed that two transmitters were not putting power forward. Some quick diagnostics showed a simple problem with one transmitter, however the other transmitter was not as easy to diagnose.
