Because yinrih language relies very heavily on subtle chances in volume, analog radio telephony–voice communication–proved much more difficult for monkey foxes than it did for humans. When radio signals bounce off the ionosphere, they can experience fading, which sounds like fluctuations in volume to the receiver.
A wireless communication system was developed, adapted and greatly elaborated from St. Redclaw's initial wire telegraphy signal system. This system is known cross-linguistically as some variation of <sFsc> /yip, long high strong whine, yip, short low strong whine/, which is an onomatopoeia meaning something like 'beep-boop'. Humans refer to the system as Vulpithecine Morse or MFSK (monkey fox shift keying, a pun on minimum frequency shift keying).
The system is based on a reduced set of yinrih speech sounds. Phonation and strength are not distinguished, and consonants are not present. What we're left with is a system that distinguishes only length and tone. Like Morse, there are two length distinctions: short and long. Unlike Morse, there are also two frequency distinctions, low and high, separated by 170 Hz. This yields a total of four symbols: low dot, high dot, low dash, and high dash.
Also unlike Morse, MFSK does not represent written language, but rather constitutes a language in its own right. Strings of MFSK symbols represent meaning directly, making it an international auxiliary language.
Much of the system borrows the cadence and tone of words from the prestige languages of the time period around the yinrih's first orbital flights.
The system was outmoded eventually as digital communication and eventually ansibles took over, but enthusiasts have kept the system alive even at the time of First Contact, and MFSK becomes a popular mode among Terran hams.