This is one in a series of question-and-answer articles about how to implement HD Radio.
Here, we query Dale Mowry, vice president of transmission systems for Harris’ Broadcast Communications Division.
RW: How do the design of Harris products for HD Radio/IBOC reflect what you learned in the DTV process?
Mowry: Digital is digital, no matter the flavor of the media. Harris has been involved in the development of digital broadcast transmission from the start for HD Radio and in the development of the North American standard for digital television with the Advanced Television Systems Committee.
The ATSC approached Harris in 1990 and requested that we develop a RF Test Bed for the Advanced Television Test Center, which was used to evaluate every advanced television system proposed for the United States.
Harris Broadcast is the only company that designs and manufactures both DTV and HD Radio transmission equipment. With majority of the installed digital transmitters carrying the Harris label, Harris has amassed a huge breadth of knowledge in digital transmission through its development of digital television transmitters in our Mason technology development center. The same teams that developed our Apex Digital Television Exciter technology have developed HD Radio technology such as the Dexstar AM/FM HD Radio exciters.
The technology for Digital Television (ATSC and DVB) and HD Radio is similar in many ways (digital modulation, RF mask compliance, linearity requirements, etc). For example, our understanding of COFDM’s sensitivities has enabled implementation of HD Radio with fewer impairments generated in the equipment itself.
Harris has designed linear broadcast transmitters for years. Harris’ understanding and experience in developing these products was helpful when dealing with amplification design elements for FM HD Radio. In the development of television transmitters, we acquired a significant knowledge base on non-linear correction and on compensating for amplitude and phase variations.
We have made a huge investment in time and money to develop digital adaptive pre-correction for digital television. We’ve learned from DTV how to design pre-correction schemes that work – we now understand the strengths and weaknesses of numerous linear and non-linear pre-correction techniques. For instance, we have used this technology to create a new low-power, AM analog/digital transmitter, DAX, which offers an exceptional digital signal.
All digital television transmitters make use of mask filtering. With DTV transmitters, we’ve had to do custom correction for mask filters and found that with the certain amplifiers the mask filter can be eliminated. And when a mask filter is necessary, we’ve found that it is a lot easier to set up or compensate for the filter when we do proper pre-correction. In fact, with good precorrection and amplifier technology, we can get more from our power modules, which can increase power and cost savings for customers.
To date, our service teams have installed more than 400 DTV transmitters, and because of the high number or simultaneous installations, Harris has made a sizeable investment in specialized digital test equipment. That investment will enable Harris to offer cost-effective installation assistance for HD Radio.
Harris has taken the lead in digital radio since its inception, beginning with the introduction of our fully HD Radio-ready DX-10 AM transmitter in 1987, which featured digital amplitude modulation, and the HD Radio-ready DX-50 in 1989. Harris introduced the first digital FM exciter, Digit, in 1993. In 1999, the first Z-IBOC transmitters were introduced and were followed by the Dexstar second-generation HD Radio digital exciter in 2002.
RW welcomes other HD Radio questions and other points of view.
