New version packet data devices support a backwards-compatible signal format. New version devices operate within a first frequency band while old version devices operate within a second frequency band. The first frequency band differs from but overlaps with the second frequency band. The new version devices may operate on a first carrier frequency (within the first frequency band) while old version devices may operate at a second carrier frequency (within the second frequency band). The new version devices and/or the old version devices may also support carrier-less modulations. Preamble, header, and trailer portions of a new version signal include a plurality of spectral copies of a baseband modulated signal. One or more of these spectral copies of the baseband modulated signal is/are indistinguishable from corresponding components of an old version signal. The payload of the new version signal may be formed in the same manner or may be formed in have a wider bandwidth, higher data rate format.