Impressions of NAB2002
Jun 1, 2002 12:00 PM, By John Battison
It would not be correct to say that IBOC was on everybody's lips at NAB, but there was considerable interest in it. I think that many people are awaiting the first real trial � the first commercial station to try it. Transmitter manufacturers were on the ball at the NAB convention and most of them had floor models to show or planned to produce IBOC transmitters shortly.
Broadcast Electronics showed the FSI 10 IBOC signal generator. It provides correct delay to match the analog and IBOC paths and encoding of the IBOC digital signal. It can be used with the FXI 60/250 series digital FM exciter and the IBOC plug-in card. Depending on the user's requirements, it will produce an FM plus IBOC output for low-level combining systems, or IBOC output only, for use in high-level combined operations.
Despite the undoubted disappointment caused by the temporary decision to recommend daytime-only operation for AM IBOC, Broadcast Electronics has introduced the ASI 10 AM IBOC signal generator. It generates the required IBOC and AM signals simultaneously. It's interesting to note that tube-type transmitters are generally not sufficiently linear for IBOC use. An audio input is split into digital and analog paths, processed separately, synchronized and encoded.
Harris displayed the Dexstar IBOC exciter. This is an interesting device that is available for AM IBOC or FM IBOC. The Dexstar exciter uses two 1GHz microprocessors. A digital up-converter creates on-channel DAB and analog signals for AM, and 10.7MHz IF DAB for FM. An RF up-converter uses the 10.7MHz signal and generates the necessary FM DAB signal. A GPS receiver provides an accurate time reference for locking synchronous systems, which yields a faster acquisition time when tuning a receiver from station to station. The Dexstar exciter is designed to produce a low-level signal output of about 1mW, which is then combined with the FM signal in what amounts to a small coupler. From there the signal goes to a linearity enhancer, then to the IPA stage and the final amplifier. Thus, expensive combiners are not required.
Nautel concentrated on AM IBOC and exhibited an eye-catching AM IBOC transmitter. An FM version is under development. Nautel demonstrated the ND 5d 5kW AM IBOC-compatible transmitter. This transmitter uses the new Nautel IBOC digital exciter, which is tunable in the AM and FM band. Also shown was the Nautel XL 60d 60kW solid-state AM IBOC DAD transmitter. Nautel has been working closely with Ibiquity in the development of IBOC, and Nautel's consistent solid-state development work seems to be paying dividends in IBOC.