Digi RF products are engineered to drive a 50 ohm load. All RF cables or antennas attached to the antenna connector should provide a 50 ohm match.
Ensure that the cable being used is rated for the frequency of the module you are using, we recommend LMR-400 cable for short to medium length cables. The longer the cable the more signal will be lost over that cable. Because of this, the length of the cable should be kept as short as possible. Often a longer serial cable can be used to minimize the length of the antenna cable. All RF cables have losses which are usually measured in dB of loss per 100 ft. Some common cables and losses are included in this table: