Context : LS 5039 is an X-ray binary that presents non-thermal radio emission .
The radiation at \sim 5 GHz is quite steady and optically thin , consisting on a dominant core plus an extended jet-like structure .
There is a spectral turnover around 1 GHz , and evidence of variability at timescales of 1 yr at 234 MHz .

Aims : We investigate the radio emitter properties using the available broadband radio data , and assuming two possible scenarios to explain the turnover : free-free absorption in the stellar wind , or synchrotron self-absorption .

Methods : We use the relationships between the turnover frequency , the stellar wind density , the emitter location , size and magnetic field , and the Lorentz factor of the emitting electrons , as well as a reasonable assumption on the energy budget , to infer the properties of the low-frequency radio emitter .
Also , we put this information in context with the broadband radio data .

Results : The location and size of the low-frequency radio emitter can be restricted to \ga few AU from the primary star , its magnetic field to \sim 3 \times 10 ^ { -3 } -1 G , and the electron Lorentz factors to \sim 10 - 100 .
The observed variability of the extended structures seen with VLBA would point to electron bulk velocities \ga 3 \times 10 ^ { 8 } cm s ^ { -1 } , whereas much less variable radiation at 5 GHz would indicate velocities for the VLBA core \la 10 ^ { 8 } cm s ^ { -1 } .
The emission at 234 MHz in the high state would mostly come from a region larger than the dominant broadband radio emitter .

Conclusions : We suggest a scenario in which secondary pairs , created via gamma-ray absorption and moving in the stellar wind , are behind the steady broadband radio core , whereas the resolved jet-like radio emission would come from a collimated , faster , outflow .