One of the shortcomings of the NanoVNA-H4 v4.3 is that it is quite easy to drop the SD card inside the case when trying to insert it. Experience is that this is really easy to do in difficult field situations or poor lighting / visibility.
This could have been prevented by better design of the moulded case.
This article describes a simple modification to make it more difficult to miss the card slot.
Above, the modification is a small block of plastic that covers part of the aperture moulded into the case, it projects 1mm into the aperture.
Above, the block of plastic is cut from 3mm acrylic and secured to the case with VHB tape. The block is 6x3x20mm, the key dimension is the projection into the case aperture for SD card access, but the 3mm dimension is important to block the space between case and SD socket.
The above pic shows the clear plastic block just meets the metal surround of the SD card slot, and there is no room for the SD card to bypass the proper slot.
In use, it has been effective… no more lost cards that require case disassembly to recover.