An injection-locked low frequency regime is established in a surface acoustic wave quartz delay line oscillator by using modulating techniques and nonlinear envelope detection. Frequency-Temperature plots shows soliton-locked type regimes with considerably enhanced frequency stability (the enhancement is at least six orders of magnitude in comparison to the unlocked one). The underlying determinism is found to arise from a resonance between the carrier frequency and that of the envelope. From the nonlinear Schrodinger model stable steps attached to the frequency -amplitude characteristic are expected in agreement with the experiment. In addition a fine structure with repulsive levels is observed. Subharmonics are found in three types of frequency ratios: Farey type levels(1/2,then 1/3,2/3...),Jain type levels at p/(2p+-1),with p integer and non rational Markov type levels ((sqrt(5)-1)/2,sqrt(2)-1)...). A toplogical explanation using hyperbolic spaces for those structures is attempted.