Nicam Digital Audio

Nicam is a 2-channel digital sound transmission system for terrestrial television. It stands for "Near Instantaniously Companded Audio Multiplex". This standard uses a 728kbit datarate for the transmission of 2 x 14bit audiosamples.
It is a very popular alternative to the regular analog frequency modulated audio subcarriers. The NICAM 728 system uses a Differential Quadrature Phase Shift Keying (D-QSPK) modulated carrier. Within ATV the center frequency of the NICAM carrier is mostly positioned at 6.552 MHz, better known as "system I" in the EN300163 standard.

In the past NICAM transmissions for amateur purposes was only possible with expensive commercial equipment until Werner (PE1OBW) designed the first well known amateur NICAM encoder. You can still find a lot of info on that design on Werner's own homepage : http://www.pe1obw.com.

This design is used by many now in the Netherlands. Later pe1jok has made a completely different design which fits on less then a standard euro-card pcb. The main difference with Werner's design is that this new one is fully written with DSP software and runs on a very modern and cheap Texas Instruments DSP. The new design has SPDIF input for direct interfacing with the coaxial output of a CD player. One other main feature of pe1jok's design is that the Nicam center frequency can be adjusted between 1.000 and 40.000 MHz with a very clean output frequency spectrum and very low error vector magnitude.

Figure 1. PE1JOK's new version of the NICAM encoder

Figure 2. Frequency spectrum of PE1JOK's NICAM encoder together with 2 FM audiosubcarriers.

More information about availability of this new design can be obtained by contacting pe1jok.