The radio detectives

‘The Radio Detectives’ series was written by A. Hyatt Verrill and published in 1922. The quadrilogy included the following books(stories), in order:
The radio detectives
The radio detectives under the sea
The radio detectives southward bound
The radio detectives under the sea

The tales begin with two lads from New York City, Tom and Frank, who are beginning to experiment and learn about radio about 1920. The boys happen to intercept messages from a mysterious source. The transmissions and the criminals creating them are a part of a greater problem facing the American people.
As the tales in these books unfold, Tom, Franks and others resolve these crimes and uncover the scoundrels by going ‘under the sea’ ‘southward bound’ finally completing the story ‘in the jungle’ of South America.