jmtillery said:
ai4i said:
jmtillery said:
All FM HD sub-channels which include HD 2 and HD 3 operate at 4% of the main channel's authorized power.
Where can I find the percentage of HD power for specific stations and whether the LSB and USB are the same?
You can find the main HD 1 ERP power specified in the station license from the FCC website. Once you have the main ERP, simply do the math calculation (4% of the main channel's ERP) and you will have the HD 2 sub-channel ERP.
All due respect, Dr. Tillery, but this is not accurate.
The power level at which an FM station runs its digital carriers has nothing to do with whether it's carrying multiple streams of audio on those carriers.
The official standard for digital power was and is -20 dBC (decibels below carrier), which translates to 1% of analog power (not of "HD-1 power," as you stated; while an HD-1 is, by definition, a simulcast of the analog signal, it's effectively a completely separate transmission path; depending on the design of a transmission system, it's entirely possible for the HD carriers to be on without any analog signal.)
For WBGG-FM, which runs 100 kW of analog power, that means 1 kW of average digital power. Those digital carriers provide 96 kbps of data throughput, and whether that's used entirely for a 96 kbps HD-1 stream or for 64 kbps HD-1/32 kbps HD-2, or a 48/48 split, it doesn't have any direct relationship to the power level at which it's transmitted. (Nor does the addition of an extra group of digital carriers for "extended mode" operation, which allows for the use of HD-3/HD-4.)
As stations discovered that -20 dBC (1%) wasn't enough to provide solid coverage, they petitioned the FCC to be allowed to increase digital power. Most stations can now request (and automatically be granted) Special Temporary Authority to go up to -14 dBC, or 4% of analog power, and with a demonstration that they won't cause impermissible interference, stations can go all the way to -10 dBc, or 10% of analog power, also under STA. Again, this has nothing to do with how many audio streams are being carried over those digital carriers.
Increasing digital power can be an expensive proposition, though, often requiring new transmitters, combiners and/or antennas to replace digital systems that were only a few years old and far from being amortized. Relatively few stations have found the investment to be cost-effective.
I do not see any STA applications in WBGG-FM's file that would suggest that the station is operating at more than -20 dBc, or 1 kW digital ERP. (To answer ai4i's question, you have to look at the station's "Application List," accessible through the FCC's own FM Query or FCCinfo.com, to find any STAs that may have been applied for/granted to cover increased digital power and/or asymmetric sideband power; and to answer Mike Sheridan's question, Clear Channel surrendered the license for the old bank building aux site a couple of years ago.)
