You should read Day of Deceit by Robert Stinnet.
We were able to decider all Japanse radio transmissions by the start of the war and were able to triangulate their fleets positions from different stations all the way fron Japan to Oahu. Not all the messages are available, but with what has been released, we can know without a doubt that the fleet did not practice radio silence.
The only surprised ones were Kimmel and Stark as this information was not passed to them.