1?) you may find on some internet sound databases the radio noises effect you need, (just a research on google with "radio noise sound" as keywords)
2?) then you just have to get a not-that-bad sound program, that can at least use two sound channels, (if you find a trial version, check first you can
save files : I wasted half an hour once working on a sound to finally realize I wasn't able to save it, because the save function was disabled on my soft version
).
3?) record the speech you would like to have as combine-like radio message (to get a wav file, or something like that),
4?) import it on the first sound channel of your sound software, and import the noise sound on the second channel,
5?) put the noise effect at the start on the voice sound, and copy/paste it at the end, then try to merge the two sounds with basic fade-in/fade-out commands, to finally get something that sounds like a radio message.