Campbell Scientific RF401-series and RF430-series Spread Spectrum Data Radios/Modems - Manual (Page 106)

Appendix K. RF401/RF411 Pass/Fail Tests
FIGURE K-1. Loop-back Test without Antennas
(9) Make sure that no antennas are attached to the RF401/RF411s
(10) Label the other RF401/RF411, “Remote”
(11) Insert jumper into the Remote RF401/RF411’s RS-232 connector pins 2
and 3 (using a U-shaped portion of a paper clip) allowing data received
from base RF401/RF411 to be transmitted back to terminal screen by
remote RF401/RF411.
RF401/RF411’s RS-232 Connector (female)
(12) Connect 12V power to Remote RF401/RF411 (Field Power Cable (Item #
14291) connected to a 12V battery (battery can be an 8 cell pack of
alkaline A, C, or D cells, or a lead-acid battery)).
If your 12V power supply is a battery pack or rechargeable battery,
make sure that the batteries are fresh or well-charged so they can
supply the 75 mA peak current needed when the RF401/RF411 is
transmitting in order to obtain valid test results.
For safety, people should maintain 20 cm (8 inches)
distance from antenna while RF401/RF411 is transmitting.
(13) Type 8 groups of 5 characters on the terminal (aaaaabbbbbccccc etc.)
(14) You should see 100% of the characters typed echo back to the screen
NOTE
CAUTION
K-4