The purpose of this field test program was to verify laboratory measurements of the effect of DABS uplink signal formats on ATCRBS transponders. The DABS interrogations tested were: (i) a combined ATCRBS Mode A/DABS All-Call consisting of a standard Mode A interragation with an additional pulse following the P(3) pulse; (ii) a DABS uplink message transmission consisting of a P(1)-P(2) pulse pair followed by 25 microseconds of 4 megabit per second DPSK data modulation. The timing aspects of these waveforms were selected on the basis of a previous series of laboratory bench tests made in a small cross-section of the ATCRBS transponder population. The results of these field measurements performed on a larger cross-section of field operational ATCRBS transponders agree with the results of the bench testing program: The recommended DABS uplink transmissions result in an effective combined ATCRBS/DABS All-Call mode and minimum triggering of ATCRBS transponders by DABS message transmissions.