Re: NPR Lab's FM-HD Power Increase Calculator

[XavierRenegade]

Re: NPR Lab's FM-HD Power Increase Calculator

How much power do you think they could increase on HD stations? I tried using the Power Increase Calculator and don't know how it exactly works. From the stations I tried it seems like most cant go above a -16 to -18DB power increase. Anything higher and stations would interfere with each other.

 

[Savage]

Re: NPR Lab's FM-HD Power Increase Calculator

Well, that's the purpose of the calculator - to predict how much additional digital power a given station could theoretically increase. It's not a "-16 dB increase." The current authorization is for digital to be -20 dBc or 20 dB suppressed below analog carrier. In the case of a station which the calculator shows could do, for example, -18 dBc, that station could only increase digital 2 dB, or the difference between -20 and -18.

iBiquity wants a tenfold increase to -10 dBc. NPR says that will increase self-interference in car radio listening and serious adjacent-channel interference - hence the "calculator." To use it just type in the callsign of the station you want to research. If in the above example the station you're interested in is cited as "- 18 dB" that means that station could only get an additional 2 dB - not enough to make any difference.

In practical terms most engineers feel even a tenfold increase to -10 dBc isn't going to do much other than cause a lot of problems.

 

[Play Freebird]

Re: NPR Lab's FM-HD Power Increase Calculator

iBiquity wants a tenfold increase to -10 dBc. NPR says that will increase self-interference in car radio listening and serious adjacent-channel interference - hence the "calculator." To use it just type in the callsign of the station you want to research. If in the above example the station you're interested in is cited as "- 18 dB" that means that station could only get an additional 2 dB - not enough to make any difference.

In practical terms most engineers feel even a tenfold increase to -10 dBc isn't going to do much other than cause a lot of problems.

As we've been discussing, a major drawback of digital broadcasting is that it's "all or nothing", so when the RF signal to noise ratio falls below the threshold of effective error-correction, it just cuts out rather than degrading gradually. Most FM IBOC coverage problems are caused by local terrain obstructions or building attenuation (foliage also plays a minor role), but in many of these cases it would take much more than a 10 dB increase to raise the signal above threshold, and needless to say the interference to neighboring analog stations would be unbearable.

The markets where IBOC reportedly works (such as Houston, Dallas, Orlando, etc.) have generally flat open terrain and many of the stations are 100 kW facilities with tall towers -- but FM also works well in that type of environment, so does digital actually provide a big advantage in audio quality? Consumers evidently don't think so.

In mountainous areas where FM coverage is severely degraded by multipath and shadowing, IBOC performance has proven very poor and I doubt that a 10 dB increase would do much good. A single-frequency network of synchronized COFDM gap-filler transmitters could greatly improve service in rough terrain, but with hybrid IBOC, a SFN also requires analog FM boosters which pose a much greater challenge. However, under BMC's proposal, SFNs would be quite easy to build since there would be no host analog signal to protect. And gap-fillers could be placed in downtown business districts to improve building penetration, offering a significant power increase where it's really needed while avoiding destructive interference. This is one major reason I'm intrigued with the BMC plan.