To start receiving digital signals, All you require is a simple software, few components to assemble,  a PC and a receiver. 

Hamcom is an excellent program developed for receiving digital signals and Morse code without requirement of an expensive modem. Software does everything for you. The hardware is a simple one IC (IC741) and few diodes & resistors.

It wont cost more than Rs.20 (50cents) to build hamcom interface for your computer. 

You will require a receiver and should know where to listen for. Sony D7600 series is ideal for low budget (Rs.5000 or so) or you may get ICOM R10 or 20 for about Rs.18000. Both has SSB mode for reception.

What you will receive? With Hamcom, you can receive Morse signals and Radio Teletype Signals. Software provides various speeds & baud rates for this purpose.

In addition to "Live" reception, Hamcom is ideal program for you to practice Morse code at home to prepare for your amateur exam. Just type in text file and start practicing receiving Morse codes.

The best part of all is, the circuit diagram required to interface your computer to your receiver is enclosed inside the software which you will find in "help - converter" menu.

Hamcom also provide you tuning scope to precisely tune incoming signals. Download HAMCOM which is freeware for all radio amateurs & enthusiasts.