Implementing MDCL

Harris offers two MDCL methodologies. The first is what it calls ACC (adaptive carrier control) and also AMC. ACC reduces the carrier level in -1dB steps (from -1 to -6dB) when the necessary modulation level is low. (See Figure 3.) AMC works as described earlier, reducing the overall output power by -3dB at 100 percent modulation (see Figure 4). According to their website, MDCL can be retrofitted in to the DX, DAX, and 3DX transmitters already in the field by the installation of a modification kit. New transmitters can be delivered with MDCL capability ready to go from the outset.

Figure 3. Typical ACC characteristic curve. Courtesy Harris. Click to enlarge.

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Figure 4. A typical AM response curve. Courtesy Harris. Click to enlarge.

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Nautel offers DCC, DAM or AMC in its AM transmitter line. The NX Series transmitters have DCC and AMC capability included as a standard feature; the user needs to turn it on. Additionally, according to information on the website, older Nautel transmitters can be retrofitted with MDCL with the addition of an NX-series DSB board that lives in a 1RU chassis. Carrier and audio levels are then sent from this chassis in to the older transmitter in order to make MDCL work.

- continued on page 4