If I had to pick between allowing HD RadioTM a 6 dB increase or removing the third adjacent protection for LPFM stations, I’d choose LPFM.
In tests performed by NPR, Ibiquity’s In Band On Channel (IBOC) digital radio scheme created significant interference to the first adjacent channel when running with 6% of the analog carrier power (-14 dB referenced to carrier) vs. the 1% (-20 dB referenced to carrier) currently allowed. The NAB has would like to see -10 dB referenced to carrier or 10% of the analog carrier power.
Remember Bill Clinton’s sign during his first election, something about the economy, stupid. In this case, it’s the Bandwidth, Stupid. In the US and Canada, FM stations are allowed 200 kHz of spectrum to transmit their analog signals. Analog signals include main channel mono (left plus right), and sub channels for stereo pilot (19 kHz) stereo matrix (left minus right), RDS (57 kHz) and any subcarriers in the 67-92 kHz range.
HD RadioTM radio requires 400 kHz of spectrum to transmit it’s digital carriers. Here come those laws of nature again, you can’t fit 400 kHz bandwidth into 200 kHz of spectrum.
Ibiquity decided to try it anyway, contravening the FCC’s rules about FM broadcasting bandwidth channels which had been in place since the advent of FM broadcasting in the early 1940’s. What they attempted to do was make the power level on the adjacent channel so low that most analog radios would not have a problem with it while there was a strong signal from another station present. (hey buddy, how about a little of this new thing called crack?) This is known as the capture effect.
Now, Ibiquity created this whole thing to make some money. Nothing wrong with that, this is a market economy after all. They marketed the hell out of HD RadioTM radio, I saw them at various trade shows, they had full page advertisements in all the trade magazines, they hit the phones, it was a full court press (it’ll make you really cool, you’ll be able to do things you can do now and you’ll feel really good). They would even reduce or waive the license fee (here, just take a little rock, try it, on me, you’ll see).
So they were able to sell a very expensive system that has significant coverage issues because of the low power levels needed to satisfy the FCC’s concerns about adjacent channel interference. The NAB and many of the big radio groups bought in to it (gotcha, crackhead, you’re mine now).
Now, of course, those that bought into HD RadioTM radio want their investment to work, (which it doesn’t right now) so all the talk of power increases and hey, lets just disregard that pesky interference issue. If you ignore it, eventually it will go away (along with the entire FM band).
The problems with HD RadioTM radio are:
- Inadequate building penetration at the current power level (1% of carrier power)
- Bandwidth that exceeds current channel assignments on both AM and FM frequencies.
- Proprietary nature of HD RadioTM‘s CODECs and licensing for second channels give Ibiquity too large a role saying how radio is broadcast in the US. Remember, radio station licenses are granted in the public interest, the owners are trustees of the public
- Complete lack of public awareness.
- It doesn’t really improve anything anyway.
By the way, shame on NPR (again) for their corporate stance contrary to maintaining good quality radio and serving public interest.
Compared to that, LPFM is a very minor thing. As I said before, removing the third adjacent protection will raise the noise floor in the FM band and by default cause more interference. However, I’ll take a little more interference created by community radio stations over the complete rack and ruin of the FM band.
4 thoughts on “The lesser of two evils”
It would be impossible for me to disagree. NPR and PBS should not receive taxpayer funding in my opinion as they always seem to come up with self-serving ideas. The local affiliates have their auctions and “bake sales” and can live without federal funding! America is broke and near bankruptcy. The LPFMs have more to contribute and I have always believed; “the more the merrier” when it comes to domestic broadcasting.
With the advent of new Digital TV broadcasting, recently there has been a proposal to collapse the standard 6 MHz. TV channels to conserve bandwidth; while the AM band is now full of man-made noise from IBOC, and the FM band is heading in the same direction. If digital broadcasting is so great, then why not re-allocate 76-88 MHz. for Digital-only broadcasting, and see how this flies?
NPR and PBS should not receive taxpayer funding
Truer words have not been spoken.
Perhaps somebody should write a petition to move IBOC to the 76-88 MHz band.
A few exaggerations in your article: Standard IBOC actually takes up 138 kHz of bandwidth total, that is 69 kHz on each side, and each of the sub-carriers are at least 45dB down (so for a 16 kW station each sub-carrier is less than 0.5 watt), it’s only when you sum all the sub-carriers’ powers that you get a total of 1% power. Each sub-carrier is only 0.4 kHz wide, so for this example of a distant first adjacent 16 kW station (at 300m), only 19 watts of that is co-channel with the 0 to 15kHz of the desired station 0.2 MHz away. If this is class B for both desired and undesired stations, they would be located at least 100 km away even if shortspaced, and normally 169 km to comply with FCC spacing. Now tell me that a 19 watt co-channel station (with white noise audio) at these distances is a serious threat to listeners within your 54 dBu contour. Granted that during trop, this may sometimes be receivable, but co-channel trope with analog audio is far more objectionable.
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John, the information I used for this article came from the NPR labs December 2009 report. It states:
“IBOC OFDM subcarriers are transmitted in two frequency bands that extend (for mode P3: Primary Main and two Extended Partitions) from 114 kHz to 198 kHz above and below the host FM channel center frequency.”
Granted, this is the worst case scenario, with three separate audio programs being transmitted in HD. One can only assume that would happen, and is happening, especially with public radio stations. I rounded up from 396 KHz to 400 KHz.
Further, I understand your statement on the ODFM subcarriers and modulation. Increasing the noise floor, which is what HD radio does, makes analog receivers less sensitive. Additionally, with the hilly terrain in these parts, it is completely conceivable that within a 54 dBu contour, terrain shadowing will create areas of low signal strength. If those areas have a better line of sight to an adjacent channel IBOC station, the radio will cut out in ways that it didn’t do before. Thus creating a perception of poor FM radio performance with the listeners.
I can only assume you meant to continue your comment, so please do. I invite views counter to my own.