VHF Digital Link (VDL) Mode 3 is a sophisticated air-ground communication system for air traffic services that had been standardized by ICAO in 2001. It is a fully digital system that can provide functionally simultaneous access to voice and data link through the implementation of TDMA system architecture. Up to the present, we have developed the airborne and ground test equipment of VDL Mode 3 system and conducted some initial evaluations. This paper reports the intermediate results of test and evaluation, which include radio interferences testing for developing frequency separation criteria as well as fundamental testing on data link and voice communication. Such results are summarized as follows;
1. As for the radio interference testing, we obtained the characteristics on squelch break and adjacent channel rejection (ACR) and assessed the impact of radio interferences by mean opinion score (MOS).
2. We confirmed that the capability of vocoder for transfer delay and error correction satisfied the standard on the vocoder. The ”step-on” phenomenon was observed at the desired/undesired signal power ratio (D/U) of 10 dB or less.
3. Preliminary measurement on fundamental performances was carried out for the test equipment. It contained the correlation of transfer delay, channel throughput and data re-transmission rate with bit error rate (BER). Also, we analyzed undesired link release that occurred during experiments and worked out possible measures to resolve it.
