  Radio observations of Gamma Ray Bursts afterglows are fundamental in
providing insights into their physics and environment, and in constraining the
true energetics of these sources. Nonetheless, radio observations of GRB
afterglows are presently sparse in the time/frequency domain. Starting from a
complete sample of 58 bright Swift long bursts (BAT6), we constructed a
homogeneous sub-sample of 38 radio detections/upper limits which preserves all
the properties of the parent sample. One half of the bursts have detections
between 1 and 5 days after the explosion with typical fluxes F>100 muJy at 8.4
GHz. Through a Population SYnthesis Code coupled with the standard afterglow
Hydrodynamical Emission model (PSYCHE) we reproduce the radio flux distribution
of the radio sub-sample. Based on these results we study the detectability in
the time/frequency domain of the entire long GRB population by present and
future radio facilities. We find that the GRBs that typically trigger Swift can
be detected at 8.4 GHz by JVLA within few days with modest exposures even at
high redshifts. The final SKA can potentially observe the whole GRB population
provided that there will be a dedicated GRB gamma-ray detector more sensitive
than Swift. For a sizable fraction (50%) of these bursts, SKA will allow us to
perform radio-calorimetry, after the trans-relativistic transition (occurring
~100 d), providing an estimate of the true (collimation corrected) energetics
of GRBs.
