Title: Collection of secret codes
Description: 7 v. in 1 ; 24 cm. ;  1. American radio service code, no. 1 -- 2. Field code, no. 1 -- 3. Field code, no. 3 -- 4. The "Hudson" code -- 5. The "Allegheny" code -- 6. The "Colorado" code -- 7. The "Huron" code.