Originally Posted by zfyoung
Maybe the other non-DRM part is some kind of digital mode(MFSK, PSK....) akin to the VOA Radiogram?
Even if it were, simulcast is not recommended for Shortwave!
According to the EBU Technical Specification ETSI TS 102 509 V1.1.1 (2006-05)
Digital Radio Mondiale (DRM); Single Channel Simulcast (SCS)
"Due to the fact that multipath propagation via the ionosphere is a typical characteristic of radio channels in HF broadcasting, the use of SCS is recommended only for LF and MF bands with mainly ground wave propagation"
The other concern here would be the receiver IF filtering.