DME Supression Lines. Because DME's and transponders share the same frequency band, a DME can interfere with a Transponder. Supression lines often connect between the 2 so that the DME is disabled during a Transponder operation. To test this possibility, just pull the DME circuit breaker for a bit during a flight when this is suspected. (Normally, only airborne will both systems be operating.) Look also for a loose or missing cable on the front of some DMEs.