  The Parkes, ASKAP, CHIME and UTMOST telescopes, which have all detected FRBs,
each works at a different frequency and has a different detection criteria.
Using simulations, we have combined the constraints from all four telescopes to
identify an allowed range of model parameters $(\alpha, \E33)$ for the FRB
source population. Here $\alpha$ is the spectral index and $\E33$ is the mean
FRB energy in units of $10^{33} \, {\rm J}$ across a $2128 - 2848\; {\rm MHz}$
band in the FRB rest frame. We have considered several different FRB energy
distributions, and also different scenarios for the scattering pulse
broadening, the event rate density variation with $z$ and the host dispersion
measure. We find that in all cases, the common allowed region includes the
range $-3.9\leq\alpha\leq-1.3$ and $0.42\leq\E33\leq1$. In all case, large
values $\alpha > 4$ and $\E33 >60$ are ruled out. Considering the allowed
$(\alpha, \E33)$ parameter range, we predict that CHIME is unlikely to detect
an FRB with extra-galactic dispersion measure $(DM_{Ex})$ exceeding $3700\,{\rm
pc\,cm}^{-3}$. A substantially larger $DM_{Ex}$ in the large FRB sample
anticipated from CHIME would falsify the assumptions of the present analysis.
Our analysis is expected to yield tighter parameter constraints with the advent
of more FRB data.
