  The presence of an extra radio background besides the cosmic microwave
background has important implications for the observation of the 21-cm signal
during the cosmic Dark Ages, Cosmic Dawn, and epoch of Reionization. The strong
absorption trough found in the 21-cm global spectrum measured by the EDGES
experiment, which has a much greater depth than the standard model prediction,
has drawn great interest to this scenario, but more generally it is still of
great interest to consider such a cosmic radio background (CRB) in the early
Universe. To be effective in affecting the 21-cm signal at early time, such a
radio background must be produced by sources which can emit strong radio
signals but modest amount of X-rays, so that the gas is not heated up too
early. We investigate the scenario that such a radio background is produced by
the primordial black holes (PBHs). For PBH with a single mass, we find that if
the PBHs' abundance $\log(f_{\rm PBH})$ (ratio of total PBH mass density to
total matter density) and mass satisfy the relation $\log(f_{\rm PBH}) \sim
-1.8\log(M_\bullet/{\rm M}_{\odot})-3.5$ for $1\,{\rm M}_\odot \lesssim
M_\bullet \lesssim 300 {\rm M}_\odot$, and have jet emission, they can generate
a CRB required for reproducing the 21-cm absorption signal seen by the EDGES.
The accretion rate can be boosted if the PBHs are surrounded by dark matter
halos, which permits lower $f_{\rm PBH}$ value to satisfy the EDGES
observation. In the latter scenario, since the accretion rate can evolve
rapidly during the Cosmic Dawn, the frequency (redshift) and depth of the
absorption trough can determine the mass and abundance of the PBHs
simultaneously. For absorption trough redshift $\sim$ 17 and depth $\sim -500$
mK, it corresponds to $M_\bullet \sim 1.05\,{\rm M}_{\odot}$ and $f_{\rm
PBH}\sim 1.5\times10^{-4}$.
