To clarify

Gamma rays have frequencies much, much higher than radio. Energy of a photon is proportional to its frequency:

E = hf, and frequency f = c/L (L = wavelength, h = 6.63 x 10^-34 J/s)

"Radio" is what we call radiation more than a few centimetres in wavelength. Then there's microwaves, infra-red, visible light, ultraviolet, x-rays and finally gamma-rays, the wavelengths of which are comparable to nuclear particles in size.

Say an average radiowave has kilohertz to megahertz [10^3s to 10^6s] frequencies, then gamma-ray frequencies are more than a trillion times higher. So for a given level of "illuminance" [energy received over a unit area] a trillion times fewer gamma rays are received. From the edge of sol space you might receive 10,000 radio photons/second, but wait 3 years or more for a gamma ray with the equivalent energy.

And then you actually have to detect the bloody thing...

Adam