Garmin portable devices can be interfaced to the SL-30 and SL-40 for remote frequency loading by using the appropriate bare wires cable. Garmin aviation portable devices have an optional accessory available for it that will allow you to interface it with the SL-30 and SL-40. Additionally, the Interface setting on the Garmin portable should be set to VHF Out. More information on the Garmin portable settings can be found in the appropriate Pilot's Guide.