Harris HT/HD+

Perhaps a new transmitter

Of course another possibility (especially if you have not invested in HD Radio at all) is to go with a new combined-amplifier transmitter. Several of the manufacturers of combined amplifiers have already published specs on their various transmitters' analog power limits with respect to the 10dB power increase. For example, the Harris Z12HD+ has an analog power limit of 2,876W in this mode. Its HT/HD+ (which is the vacuum-tube combined amplifier) tops out at just under 8,200W of analog power in this mode. Harris recently introduced the HPX40, which was designed with increased IBOC levels in mind. This transmitter will produce 16kW of analog power in the -10dBc mode, making use of the standard PAPR algorithm.

Nautel has developed a different version of the PAPR (peak to average power ratio) reduction algorithm for use in its IBOC transmitters and thus has different set of published specs for the amount of analog power its transmitters can generate in the -10dBc digital mode. For example, the NV20 will deliver up to 8.8kW of analog power in this mode; the NV40 will go up to 17.5kW.

Nautel NV Series

I have learned from Broadcast Electronics that its current set of solid-state combined amplifiers can be operated in the -10dBc mode, with the obvious reduction in analog output power capability. Like BE, Continental Electronics is taking more of a conservative, wait-and-see approach as to where higher digital levels really end up before publishing elevated level performance specs on their vacuum-tube combined amplifiers.

If you currently use a separate antenna for HD Radio (often referred to as space combining) then your ability to move up in power by 10dB is probably going to depend mainly upon how much TPO you currently generate. If it was difficult to find the right amount of floor space, electricity or air conditioning for the current HD Radio transmitter, how easy is it going to be to increase it by 10dB? Is there the necessary amount of isolation between the main and auxiliary antennas? These are obviously very site-specific questions. One possible solution may be to change your auxiliary antenna to one with higher gain. This will not only lower your TPO requirement, but could also increase the isolation from your main antenna as well.

Broadcast Electronics FMi Series

The split-level combining method will likely be problematic when trying to increase digital power because there generally isn't that much headroom available in either the IBOC amplifier or the analog transmitter. Assuming there is some amount of headroom available in the current IBOC amplifier, one possible solution would be to add a second (identical) IBOC amplifier with a 3dB hybrid combiner to increase the overall IBOC power. This would obviously necessitate extra space, ac power and air conditioning at the site.

I've used the -10dBc levels because it provides the most stringent requirements. It's certainly possible that the amount stations are allowed to increase is going to be less than that, making the solutions to the problems associated with increasing HD Radio power considerably easier. I'm a believer in HD Radio — not only in the efficacy of the technology, but in its future importance to our industry. If we continue to make it available to the radio audience, I believe it will experience a continually increasing level of acceptance. It took FM radio 20 years to catch on after all.

Irwin is transmission systems supervisor for Clear Channel NYC and chief engineer of WKTU, New York. Contact him at doug@dougirwin.net.

Resource Guide

HD Radio transmitter and antenna manufacturers