Elecraft KXFL3 Filter Option - Manual (Page 11)

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If you installed the internal test antenna to use the internal 16MHz signal for calibrating, open the KX3 and
carefully remove it.
 Be sure to tighten the screw on the battery retainer (see Figure 2, page 5).
 Remove the protective tape from the plug to the BNC connector and replace it in the RF board
connector (see Figure 5) or, if installed, the KXAT3 connector (see Figure 6).
Figure 5. Connecting the Antenna Plug to the RF Board - No KXAT3 Installed.
Figure 6. Connecting Antenna Plug to KXAT3 Board.
Replace the batteries (if desired), close the case and tighten all four thumb screws.
Replace the KXPD3 paddles (if desired). Take care not to bend the connector pins in the KX3.
That completes the Calibration Procedure.