Upping HD Radio signal strengths

The possible rulemaking proposal for increasing power on FM HD Radio signals: What does it mean at the station with engineering and costs involved? What does it mean in improved building penetration and reception distance/robustness of FM signals? We asked BE’s Tim Bealor and Cavell, Mertz & Associates’ Gary Cavell.



Cost considerations for increasing HD Radio another 10 dB

Broadcast Electronics has been receiving calls from broadcasters asking about the proposed 10 dB HD Radio power increase.

There’s no question that turning up HD Radio another 10 dB would give digital FM that extra oomph needed to penetrate buildings and to broadcast out to fringe coverage areas.
  
We’re talking a tenfold increase in digital power, after all.

We are currently in the discovery stage of this new HD Radio proposition. Broadcast Electronics is part of the coalition of broadcasters exploring the HD Radio power increase proposal, and we have been focusing our R&D on new technologies that will produce greater transmitter efficiency in the ongoing quest to produce more power for less.

Although there are more questions than answers as of yet, there are important cost considerations when implementing HD Radio at higher output powers. Foremost, it’s important to realize that, watt-for-watt, HD Radio is more expensive to transmit and cool than traditional FM, especially as the station increases in power.

The short math given what we know today is that it will cost roughly double on the transmission end to increase HD Radio FM power tenfold. There are likely to be additional costs for cooling and air handling as well, in order to dissipate the excess energy required to get out another 10 dB in HD Radio signal. And, for some higher powered stations, existing HD Radio configurations may not be able to handle the power load, which could add to the cost and complexity of increasing HD Radio beyond its current power level.

In some cases, an incremental power increase of 3 dB or 6 dB may make more sense than a full 10 dB increase. Consider a 20kW FM station. Under the current HD Radio scenario, and depending how the transmission path is configured, the typical 20kW station is running 2kW to produce the needed 200W of HD Radio in a high level combined system under the current allowed -20dB power ratio. (HD Radio is 1% of the existing FM output.) There’s a 90% excess because of how the digital and analog signals are combined together through a typical high level combined system. 90% of that 2kW from an HD radio transmitter is rejected as heat load, along with the equivalent 10% from the FM analog side.

Add a full 10 dB power increase into the equation, and that 200W turns into 2kW allowable HD Radio power (or, 10% of the existing FM output, compared to 1% today). 2kW doesn’t seem like much, until you add in the exponential HD Radio power factor. In order to produce the desired 2kW of HD Radio power, we are no longer talking a 2kW or a 4kW or even a 10kW transmitter. A full 20kW transmitter is needed to produce the 2kW HD Radio signal. What’s more, the vast majority of this power, or 18kW, is dissipated in heat, another factor that drives up costs, not to mention the excess utility costs to produce this power in the first place.

Also worth considering is existing transmitter combiner technology and whether or not it can support the added demands of increasing HD Radio broadcasts another 10 dB. If not, then it’s very likely that stations at the higher power levels will need to factor in a new antenna system that can support HD Radio, rather than piggyback onto their existing FM antenna system.

At the higher powers, especially, an immediate 10 dB increase in HD Radio signal may be cost prohibitive. In these cases, the better option may be to add more HD Radio in power increments of 3 dB or 6 dB, with an eventual 10 dB power increase planned out over a 10 or 15 year period. BE’s recently introduced ESP transmitter technology, for example, enables broadcasters to get more power out of their existing BE transmitter to provide the needed flexibility in the event they want to make those incremental jumps up in HD Radio power with the least amount of impact to transmission hardware. Other new technologies built into our new FXi 60/250esp digital exciter likewise make it easier and more economical for stations to increase power incrementally, as well.

The economics of HD Radio adoption is perhaps the single most important consideration for broadcasters today. It is for this reason that we have invested a good portion of our R&D budget on HD Radio cost containment efforts. A great example is our new FM digital exciter, the FXi 60/250esp, which is capable of driving two transmitters. One exciter for two transmission paths will save broadcasters $20,000 or more in implementation costs. This is also the reason why BE is working with the National Association of Broadcasters on behalf of our broadcast customers to standardize HD Radio as a technology, which directly transferred to cost savings recently with the introduction of a new BE “embedded” exporter that shaved thousands off HD Radio implementation costs.

Between BE’s ongoing quest to drive down the capital cost and ongoing operational expense of HD Radio equipment, and broadcasters’ willingness to innovate, it is very likely that radio will realize an ever-expanding range of digital options at more affordable price points as the digital transition continues.

Tim Bealor is Vice President, RF Systems Broadcast Electronics
Quincy, Il.

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Why increase HD Radio’s signal strength?

Since well before last fall’s NAB Radio Show, there has been much discussion and speculation regarding the anticipated Rulemaking Proposal for a power increase in the digital portion of the FM HD Radio signal (from 1% of the analog power level to 10%). As of this writing, nothing has been filed with the Federal Communications Commission, but there is an expectation that something will be formally proposed soon. The impetus for this effort has been the growing realization that digital coverage does not extend as far as analog nor does it succeed as well in building penetration. Further, the added program streams (HD-2, HD-3) suffer apparent signal “dropout” more rapidly than the main (HD-1) stream. All of this has caused much frustration at the consumer, and consequently, the station level. A presumably “simple” answer is to add more transmitted power, which is the crux of the proposal at hand. However, because of the nature of the digital medium, the proposed tenfold increase in digital power will likely necessitate a doubling of transmitter power (roughly), which may rule out some (or require other) methods of transmission system architecture. The ultimate bottom line is, if we as an industry wish to stay competitive with the ever increasing alternatives for our listeners, then we will have to face the very real need to embrace digital technology and transmission systems…and soon. Accordingly, thoughtful planning is necessary to be able to adopt HD Radio in our stations now, while providing for an easily implemented upgrade path whenever the rulemaking process sorts itself out.

By way of background, it is important to recognize that there have been considerable efforts undertaken within the broadcast industry by equipment manufacturers and various broadcast stakeholders to think about making HD Radio more viable. Once the idea of a power increase started to gain traction, even more work has been taking place to understand the ramifications as well as to prepare for this change, presuming of course, that something will eventually come to pass at the FCC level. This writer is of the opinion that there is still a lot of work to be done on the practical side before there are any rules in place, but I have to believe that something along these lines will eventually come to pass. So it is wise for the savvy station owner, manager, and engineer to start think about and preparing for “what might be” – even now. Fortunately, some reasonable, albeit preliminary impressions can be formed from digging through the various papers and presentations that have been made public so far.

Again - why is this power increase even being considered? Frankly, the reasons are many and principally spring from the bitter experiences of the “early adopters”.  First, as a learned friend of mine is wont to say, “…in the next few months, terrestrial radio will be the only analog broadcast service left.”   He’s got a point. With the rest of our world “going digital”, and embracing the opportunities that digital provides, doesn’t it really make sense to jump in and become part of this transition? Radio is facing increased competition from all sides - from the Internet, WiFi, hand held devices, and the like. Yet our radio industry is still hanging on to its single stream per carrier mode. Ask your kids (or younger co-workers) where they learn about new music. Ask them what they use to listen to music. Is it still radio? Will it still be for much longer?

Second, the presently authorized FM Hybrid Digital (“HD”) mode limits the digital power to 1/100th of the primary analog station’s power. Not surprisingly, anecdotal and increasing scientific information, is suggesting that the companion HD Radio coverage “footprint” does not reliably extend as far as the corresponding analog coverage. Effective distant coverage reach is very important to broadcasters since larger range equals more listeners. Having the companion digital signal “blend” back to analog because the digital portion doesn’t “carry as far” is often a disadvantage since people who are becoming more interested receiving in the better quality signal we all have been talking about on the air are disappointed to not receive it!

Third, there is a growing interest in HD-2 and HD-3 channels, which can provide alternative program streams, making us more competitive with other existing and emerging services. Unfortunately, these extended channels suffer from something called digital “cliff-effect”, by not having a fallback analog backbone available. Simply put, HD-2/3 coverage is essentially “lost” long before the end of the listener’s anticipated “signal reach”. This can be, and has been, a complication and an embarrassment to stations that are actively promoting and cultivating their additional digital streams.

Fourth, limited building penetration with the modest digital signals can be an annoyance, if not a complete listener turn-off (literally). Given the ready alternative in an office/home environment of the Internet, you’ve potentially lost a listener forever. They’ll sample once, maybe twice, and the go away if it’s too hard to deal with your station.

Finally, there is more and more interest and development of hand held devices which are designed to receive data streams (i.e., information and entertainment) from a variety of sources such as cellular networks, WiFi, WiMax, and even (hopefully) radio and TV BROADCASTERS. Indeed, many hand held device manufacturers are paying attention to the possibility of incorporating necessary FM tuners into their products, however, the effectiveness of the necessarily small associated receiving antennas will not be as great as that which can be enjoyed with other receiving devices such as car, portable, and desktop radios. Unlike a cellular-type network, which uses towers that are plentiful and close together, broadcasters must cover their entire regions with a single “stick”.

So more power simply translates into increased chances to overcome these apparent issues. And yes – we, as broadcasters, need to keep up with these competing entertainment streams in order to stay relevant and profitable in this digital age.

Unfortunately, I hear way too many stories about consumers getting interested in HD Radio, actually buying a receiver, only to be turned off by rotten reception (and admittedly other issues, such as intermittent/unreliable program streams or unimaginative content). Frankly, you only have one chance to make a first impression and we often are failing in the attempt. Increased digital power, if it can be reasonably accomplished, and without a material interference penalty to the analog listeners, would certainly help at least one of these factors.

But what does higher-powered HD Radio implementation mean at the station level in terms of engineering and capital costs? The early work of some of the transmitter manufacturers indicates that increasing digital power will require a significant “de-rating” of transmitter power.1 This will typically mean the addition of another similarly rated transmitter (using a combining technique) or the purchase of a new transmitter of roughly twice today’s power level.
The good news is that the various transmitter manufacturers seem to be working hard on improving their technology, so when (and if) the rule change is adopted, perhaps the story will be less dire. Stay tuned, as they say.

There are other “nuts and bolts” issues that you should talk to your engineer about. For instance, present wisdom suggests that the “low level” or “common amplification” method, which is typically used for stations requiring transmitter power outputs below about 10-15 kW, may be one of the easier methods to implement under a higher power scenario.

“Space combining”, where separate transmitters and antennas are involved, appears to be the best option for higher-powered installations. However, isolation between the two antenna systems becomes more critical and specialized antenna designs/feed systems may be required.

At the higher digital power levels, “high-level” combining methods (where the analog and digital transmitters are fed into a “hybrid combiner” where the signals are married and then fed to the antenna) are a problem since the involved physics requires that much of the power be wasted (sent to the “reject load”). Given the consequential (markedly) increased heat load, this option becomes less feasible.  Other “legacy” methods are still being debated, but presently, these seem to be destined to be discarded for various reasons.

Those folks in the trenches of the real world, and particularly those in the middle and small markets dealing with a recession economy, competition from other entities and limited technical staff and financial resources, are still questioning the wisdom of implementing HD Radio in their markets at all. I don’t know that I particularly blame them. But I would also suggest that not adopting digital radio broadcasting may not be wise given increasing competition for other program stream providers – even in the middle to small markets. The problem is, you may ultimately risk losing those “ears” to the “new media”.

Similarly, those who are wondering whether they should defer their HD Radio implementation until this power increase matters sorts out may have a long time to wait, given how slowly things can move in Washington. Although “future proofing” your station is truly impossible, your best bet is to confer with your station engineer (or consultant) and your favorite equipment manufacturer to see if there may be some implementation/upgrade paths that would make any transition to the higher digital power levels a bit easier if and when the time comes.

Footnote: 1. This is due to the nature of the digital signal carriers, how different RF amplifiers operate, and the need to keep “undesired” emissions and distortion within FCC limits. In particular, increasing digital power requires additional “reserve” transmitter power (“headroom”) in order to handle the corresponding increase in peak-to-average AM component of the digital signal – thus keeping from operating the transmitter in a non-linear region, which would destroy FCC emission mask compliance.  In actual practice, the proposed power increase may require something in the order of a 50% reduction in rated power.

Gary - aka - Garrison C. Cavell
President, Cavell, Mertz & Associates, Inc.
7839 Ashton Avenue, Manassas, Virginia  20109-2883
703.392.9090   gcavell@CavellMertz.com
www.CavellMertz.com   www.FCCinfo.com