A Few Words About IBOC / HD Radio™ Implementation:
As more and more stations implement HD Radio™, broadcast engineers are learning that successful implementation depends on high-quality equipment. Simply being able to “pass an IBOC signal” is not enough. A quality hybrid analog/digital signal requires strict adherence to good antenna and filter design principles. Shortcuts in antenna tuning that were acceptable in the past, such as tuning the radiator high for ice, slug tuning, and unbalanced or asymmetrical radiators are now proving unwise and costly. Poor design not only affects the coverage patterns of both signals, it can also make implementation unnecessarily expensive. Consider, for example, that a simple 3 dB difference in antenna isolation can add $10,000 to the price of an isolator.
Since the early 1990s, broadcaster have been depending on Shively Labs to solve their IBOC implementation problems. During that time, we have pioneered a number of techniques and equipment designs that are industry standards today. These include the square wave mask filter - the first transmission component licensed by iBiquity, precision 10-dB injectors that do not require additional filtering, the low-power FM interdigital filters for IBOC filtering and combining, digital harnesses for back-fitting panel antenna systems without the need of retuning, and interleaved analog-digital antennas. It also includes the development of a number of techniques, including back feeding digital through balanced combiner systems and split feeding combiners to allow analog and digital signals to be swapped in the case of emergencies.
These successes were no accident. Shively Labs antennas and filters are designed from the ground up to produce the performance required for successful HD Radio™ implementations without short cuts and gimmicks. And, as always, we never lose sight of the most fundamental principle of FM transmission – your audience needs to be able to hear you.
Some Useful Links:
- IBOC Injection Calculator. Calculate the power levels for your IBOC injection project.
- IAD Interleaved Analog-Digital Antennas. Winner of both a BE Radio 2002 Pick Hit Award, a Radio World 2004 Cool Stuff Award. Used by more directional stations than any other interleaved antenna.
- Model 5626 10-dB Injector. The industry’s best performance – no filtering or matching networks have ever been needed with Shively injectors!. Link also includes data on 9, 8, 7 & 6dB injectors for mid-level combining.
- Model 2606 interdigital filters, 2630 interdigital branched combiners, and 2640 interdigital balanced combiners - featuring the industry’s best performance at one-third the size of existing systems
- Isolators – a Short Course. Learn the basics of isolator sizing and why poor antenna design can add unnecessary expense.
- Separate Antennas for IBOC Transmission. One of the most economical and successful techniques for IBOC implementation. This method was chosen for the HD Radio™ demonstrations at the 2004 and 2005 CES Shows, as well as the first ever demonstration of multicasting at NAB2005. For a list of the FCC requirements for broadcasting IBOC over separate antennas, see below.
- Basics of FM Combining Systems.
- Back-feeding digital through balanced combiners. Read the article about the tests that proved the viability of this technique that is an industry standard today, and for a more in-depth discussion, the tech bulletin explaining the process.
- Split Feeding – we took back-feeding one more step to allow redundancy for both the analog and digital transmission lines, balancing the line loads, and minimizing the size of the lines required.
FCC Requirements for IBOC Transmission over Separate Antennas:
The FCC allows IBOC implementation using separate antennas provided they meet certain criteria:
- The digital transmission must use a licensed auxiliary antenna.
- The auxiliary antenna must be located within three seconds latitude and longitude of the main antenna.
- The vertical separation of the antennas must be limited such that the auxiliary antenna is within 70 and 100 per cent of the height above average terrain of the main analog antenna.
HDRadio™ is a trademark of iBiquity Corporation.
Last updated: 11/07/06
Webmaster: Al Friend
© copyright 2006 Howell Laboratories, Inc.
