New NPR power calculator available (unofficially)

[briankay]

http://www.nprlabs.org/publications/distribution/interimIBOCpowerallowance/index2.php

Looks like a lot of stations will be able to turn up to the full -10 dBc even in the Chicago market.  Some can do the full -10dBc on only one of the sidebands. This could make some frequencies more valuable than other depending on how much they can their power.

At -10 dBc would be an enhancement to reception in a way -20 dBc never was. Of course that is if you have a HD radio. It would be nice hearing digital stereo for a change instead of picket fence analog mono in the peripheral areas near the 60dBu to 54dBu contours. It's probably already just a couple of dollars to add the HD radio chip in an in-dash receiver. So let's see if the auto manufacturers step up. They're probably the catalyst to get the change over to digital radio underway. They might well do it soon when they see more solid digital coverage but only if stations bump up to full digital power.

[BRNout]

There goes my reception of several Milwaukee market signals that I apparently have no right to enjoy! 

The sooner this IBOC garbage hits the dustbin the better.  It's getting out of hand with so much of the band compressed so that 0.3% of the audience can receive "HD" signals. 

And, for the $64,000,000 question: how does all this play into the FCC's latest hobby of low power FM?

[tommygraser]

This is Great!!!! turn up the POWER baby I got my HD READY!!!!

[Play Freebird]

http://www.nprlabs.org/publications/distribution/interimIBOCpowerallowance/index2.php

Looks like a lot of stations will be able to turn up to the full -10 dBc even in the Chicago market.  Some can do the full -10dBc on only one of the sidebands. This could make some frequencies more valuable than other depending on how much they can their power.

Thanks for posting the link.  The important number to keep in mind is the "D/U Ratio" in the second to last column in the second box.  This represents digital-to-analog interference to each adjacent channel neighbor from the upper or lower IBOC sideband of the station under study.  In reality, this is co-channel interference and cannot be eliminated through improvements in receiver selectivity. 

For many years, FCC allocation standards have been based on a 20 dB co-channel D/U ratio, so a value less than 20 should be considered problematic.  And if that number is low enough to be negative, expect a disaster.

For some examples of severe interference, here are several stations in the Northeast:

WKTU (which transmits from the Empire State Building); look at the effect on WPRB and WNNJ.  There's plenty of population in those interference zones.

WDAS, Philadelphia vs WIOV

WUSL, Philadelphia vs WAWZ

But for that matter, WAWZ vs WUSL.  (Hope they both remember Luke 6:31)

WENJ vs WPEN-FM

WAEB-FM vs WPPZ

WJFK (near Washington) vs WWMX and WWEG.  Ugly!

Of course, grandfathered stations will also cause a lot of trouble.  Check WTSS, Buffalo vs WLGZ, WVOR, and WNAE-FM.

Or, WNTQ, Syracuse vs WCIZ in Watertown.    I also wonder about the impact on Canadian stations which apparently aren't taken into account here.






 







 

[Len14043]

It is interesting that on the initial NPR calculator, most or all of the stations in the east and midwest could not be increased beyond the current -20 db power level. With this new calculator, most of the stations can now raise their power up to -10db. Could someone explain what the information in the 2nd and 3rd column from the left means, i.e. F(50,10) dBu and D/U Ratio. I think the D/U ratio is the relationship between the IBOC sideband and the analog signal, but is that the ratio at the 40, 50 or 60 db contour?

[Play Freebird]

It is interesting that on the initial NPR calculator, most or all of the stations in the east and midwest could not be increased beyond the current -20 db power level. With this new calculator, most of the stations can now raise their power up to -10db. Could someone explain what the information in the 2nd and 3rd column from the left means, i.e. F(50,10) dBu and D/U Ratio. I think the D/U ratio is the relationship between the IBOC sideband and the analog signal, but is that the ratio at the 40, 50 or 60 db contour?

It appears that "F(50,10) dBu" refers to the predicted field strength of the IBAC digital sideband at the edge of the first-adjacent station's service contour.  For a commercial Class B, the service contour is 54 dBu, for B1 it is 57 dBu, and for all other classes 60 dBu. 

As I mentioned in my last post, the D/U Ratio (Desired analog / Undesired digital) provide the means to evaluate co-channel interference to the first-adjacent's analog signal; any number less than 20 represents a reduction in protection from normal FM allocation standards.  If the number is negative, then the digital sideband would surpass the strength of the "protected" station's analog.  Better receiver selectivity won't help in situations like this.

In the past, NAB made a big deal about similar proposals (for example, the Class A power increase to 6 kW) but they're obviously ignoring the negative impact of this change.  However, to divert attention, you'll soon see a renewed fuss over the LPFM third-adjacent issue. 

[briankay]

I think the D/U presented is the with reference to the main analog signal. As the digital power will be -10 dBc max, you can add 10 dB to that D/U ratio to get the co-channel interference amount. So if D/U is 10 dB in real terms it's 23 dB. The extra 3 dB takes account that the digital power is divided between the 2 sidebands. Each sideband having half the total digital power. So station at full digital power will be -13 dBc on each side band or in otherwords 5% of the analog power will be co-channel to the "victim" station if my rough understanding of this is correct.

The proof will be in the pudding though.

[Len14043]

Despite not being an engineer, I think I figured out the rationale behind the NPR calculator. A full -10 db power level would be permitted as long as the D/U ratio remains above +10.  If the D/U ratio is less than +10 db, the allowable digital power is decreased incrementally until the -14 db level is reached, after which the protected station would not receive additional protection - even if the D/U ratio is less than zero.  

[Play Freebird]

I think the D/U presented is the with reference to the main analog signal. As the digital power will be -10 dBc max, you can add 10 dB to that D/U ratio to get the co-channel interference amount. So if D/U is 10 dB in real terms it's 23 dB. The extra 3 dB takes account that the digital power is divided between the 2 sidebands. Each sideband having half the total digital power. So station at full digital power will be -13 dBc on each side band or in otherwords 5% of the analog power will be co-channel to the "victim" station if my rough understanding of this is correct.

The proof will be in the pudding though.

And if the pudding tastes like crap, will we all be forced to swallow it? 

Out of curiosity, I started up my contour-plotting software and looked into this some more.  Turns out that the D/U ratios shown in the NPR calculator are determined at the "victim" station's 60 dBu contour, regardless of class -- and as you suspected, they're based on analog power with no adjustments made for the specified IBOC injection level. 

Taking WUSL, Philadelphia as an example, the F(50,10) analog interference contour at the edge of WRKS's 60 dBu service contour is 52 dBu.  As you mentioned, assuming a nominal IBOC injection of -14, the lower sideband would be down another 3 dB; therefore, the predicted digital interference field strength (falling in WRKS's channel) is 35 dBu.  So at the 60 dBu contour, WRKS would have a D/U ratio of 25 dB which should be adequate (except in the summer when "ducting" conditions exist many evenings.)

But at the WRKS 54 dBu contour (normally-protected service of a Class B commercial station) WUSL has an interference contour of 57 dBu. Subtracting 17 dB to adjust for digital injection, this works out to 40 dBu, leaving WRKS with a D/U ratio of only 14 dB on their analog channel.  The normal protection requirement is 20 dB, so there will be a significant loss of service in these areas.  To the listener, it will sound as if WRKS has decreased power.

WUSL's larger issue is the interference to WAWZ in Somerset County, NJ.  At the edge of WAWZ's 60 dBu contour, WUSL has a 71.2 dBu interference contour.  Subtract 17 dB from that and you get 54.2 dBu, leaving WAWZ with less than 6 dB D/U on their own channel.  This will certainly result in a mutual increase in interference.  At the WAWZ 54 dBu contour in Bucks County, PA the signal will be practically unusable on mobile receivers.  Depending on local terrain, this may also affect WAWZ listeners in the NJ counties of Hunterdon and Mercer, well within the 60 dBu.

IBOC proponents will argue that these first-adjacent short spacings have existed for years and nobody has ever enjoyed full protection.  However, ongoing improvements in receiver selectivity have really helped to resolve first-adjacent analog-to-analog spillover, particularly in car radios.   Much of this effort is about to be negated, just as we've seen in the AM band.

A good slogan to keep in mind:  With IBOC, first-adjacent is the new co-channel.

[Len14043]

Thanks for posting the link.  The important number to keep in mind is the "D/U Ratio" in the second to last column in the second box.  This represents digital-to-analog interference to each adjacent channel neighbor from the upper or lower IBOC sideband of the station under study.  In reality, this is co-channel interference and cannot be eliminated through improvements in receiver selectivity. 

For many years, FCC allocation standards have been based on a 20 dB co-channel D/U ratio, so a value less than 20 should be considered problematic.  And if that number is low enough to be negative, expect a disaster.

Although the co-channel interference cannot be eliminated through improvement in selectivity, what about improvements in the capture ratio?