This paper compares three candidate detection techniques for shaped offset QPSK (SOQPSK-TG) and Feher's QPSK (FQPSK-JR) modulations which are embodied as fully interoperable modulations in the Interrange Instrumentation Group standard IRIG-106. The techniques are based on a common trellis-coded modulation representation and a common continuous phase modulation (CPM) representation for these two modulations. In addition the pulse amplitude modulation (PAM) decomposition of the common CPM representation is developed. All three techniques achieve near-optimal bit error rate performance. The PAM-based detector offers the best performance-complexity trade-off.