When browsing hellocq, I saw the personal signature of BD4JK, as shown in the image below:
The "BG4-2-066" in the first line actually touched upon my knowledge gap. The combination of letters and numbers doesn't seem like a call sign at all. Instead, it reminded me of an SWL number.
Therefore, I dare to speculate that this could be a Level 5 license obtained during the CRSC era, which lacked launch authorization, and was therefore issued by regulatory authorities as a type of "listener" identification similar to SWL.🤔
Please also seek clarification from experts!😄
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