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+--- Thread: Question about the "shift" value in System BLUE raw signal data (/showthread.php?tid=4332)
Question about the "shift" value in System BLUE raw signal data - THara_Chiba - 2026-11-09
Hello,
I am a graduate student at Chiba University, Japan. I am analyzing raw H-field waveforms from station 3005 (System BLUE, main board Ver 19.5) recorded on 10 July 2025.
According to the UDP format description, the 12-bit samples are sent as 8 bits, and "shift" is the lowest value at which all samples of the record fit. So the original value should be (8-bit value) x 2^shift.
However, our data do not seem to follow this:
1. Records of nearby lightning (within 30 km) are almost all shift 0, and many of them are saturated at 0 or 255. With the lowest-fitting rule, a larger shift should have been chosen.
2. The background noise before the trigger becomes exactly 4 times larger for each shift step, when read as (8-bit value) x 2^shift.
3. Read in the same way, the product (distance x time integral of the field) increases strongly with distance. If we additionally divide by 4^shift, it becomes almost independent of distance.
Could you tell me:
- Is there any automatic, per-record gain change in System BLUE, in addition to the amp settings?
- If the station is in automatic gain mode, is the gain adjustment related to the shift value?
- If so, how should the recorded values be converted to a common scale?
I attached three figures (a saturated record, the shift statistics, and the distance comparison).
Thank you very much for your help.
Best regards,
Tenma Hara
Chiba University, Japan