Viavi ATC-601 (IFR/Aeroflex) Transponder Test Set Review | AvionTEq 10 June 2025 AvionTEq Blog Learn about the ATC-601 transponder test set by Aeroflex/Viavi. Ideal for Mode A/C testing, this portable unit is trusted by avionics technicians worldwide. Available at AvionTEq. [More] Share