INTERFERENCE AND PERSPECTIVE

[Len14043]

All the talk of interference and whether it exists depends of your perspective. While reading the FCC order authorizing the digital power increase, it mentions that operation at -20 db was interference free, and test stations operating at -10 db didn't receive any credible complaints of interference. But if you talk to an FM dxer, the interference is intolerable at any level. Then there's the issue of interference in a legal sense which refers to the protected contour. Interesting.

 

[Play Freebird]

All the talk of interference and whether it exists depends of your perspective. While reading the FCC order authorizing the digital power increase, it mentions that operation at -20 db was interference free, and test stations operating at -10 db didn't receive any credible complaints of interference. But if you talk to an FM dxer, the interference is intolerable at any level. Then there's the issue of interference in a legal sense which refers to the protected contour. Interesting.

I suspect there was some "cherry picking" of test stations. If you dig into the CDBS database and note how many stations received experimental authorizations during the test period, and then compare with the stations mentioned in the rulemaking petition, it appears there may have been unfavorable results at some locations that the proponents didn't want to discuss.

Of course, the other reason IBOC interference may go under-reported is that it resembles white noise on an FM analog receiver. The casual listener thinks the desired signal is just fading out, rather than affected by "QRM", but DX-ers have a better understanding of the source.

 

[jhardis]

I suspect there was some "cherry picking" of test stations. If you dig into the CDBS database and note how many stations received experimental authorizations during the test period, and then compare with the stations mentioned in the rulemaking petition, it appears there may have been unfavorable results at some locations that the proponents didn't want to discuss.

I would be greatly appreciative of examples -- and sooner rather than later.

Thanks,
Jonathan

 

[RadeoEngineer]

All the talk of interference and whether it exists depends of your perspective. While reading the FCC order authorizing the digital power increase, it mentions that operation at -20 db was interference free, and test stations operating at -10 db didn't receive any credible complaints of interference. But if you talk to an FM dxer, the interference is intolerable at any level. Then there's the issue of interference in a legal sense which refers to the protected contour. Interesting.

I've been in a situation with analog interference by a Mexican licensee with documentation presented from tests I made utilizing a Tektronix 2710 spectrum analyzer, and backup documentation from an independant consulting engineer that I hand presented to the local EIA and followed up with the proper paper complaint of same. The fact is that the interference was there There was nothing subjective about it. That a listener wouldn't make a complaint to the FCC is irrelevant to the factual interference. Of course the FCC did very little regarding the issue because the "public" was not engaged. The Feds definition of "credible" in reference to a member of the public filing a complaint seems to be a great method for them to ignore the actual credibility of known, competent engineers with very high quality test equipment other than a boombox at the beach. It frees them up to count their "regulatory fees" money and plan their office budgets.

 

[BRNout]

That's an excellent point RadeoEngineer! I was confronted by a Mr. Tom Ray (many of you probably know him) on another one of these boards about this issue; basically he didn't care for my comments about the increase in power for FM HD signals. One of his statements (having to do with the above-mentioned tests) was that not one complaint was received by the FCC. It basically ended his missive like a QED - supposedly trumping any other argument that I could make about the subject.

To me, that argument says NOTHING about the existence or non-existence of interference, but to the FCC it is an excuse to look the other way. How many listeners are going to take the time to file an FCC complaint over something like this? How many will even understand why the fringe station that they enjoyed before is now gone? Perhaps it's their radio or the guy next door or their car battery. Heck, I am a radio geek and I have never thought to complain to the FCC about anything. I wouldn't even know how to start the process.

So this argument is bunk. Only folks in the industry, generally on the corporate side, would ever complain to the FCC. And, we all know it.

 

[Len14043]

Again, interference is a matter of perspective and is in the ear of the beholder. Anytime a station is added, whether its a LPFM or a short spaced shoehorned in station, that causes interference. When I am listening to my favorite talk show while driving, and the station becomes unlistenable because of co or adjacent channel stations, the interference is real to me, but is not considered interference in a legal sense. It is up to the FCC to determine what is interference, and somebody has to make the call. If dxers ran the FCC, there would be no digital stations, and probably no LPFMs. Most of the posters here are dxers and I understand their concern. If I was an FM dxer, I wouldn't want any digital interference on the band. But then, dxers probably represent less than 1% on the radio listening public, and the needs of the entire industry need to be taken into consideration. The FCC has spoken loud and clear.

 

[audioguy]

Again, interference is a matter of perspective and is in the ear of the beholder. Anytime a station is added, whether its a LPFM or a short spaced shoehorned in station, that causes interference. When I am listening to my favorite talk show while driving, and the station becomes unlistenable because of co or adjacent channel stations, the interference is real to me, but is not considered interference in a legal sense. It is up to the FCC to determine what is interference, and somebody has to make the call. If dxers ran the FCC, there would be no digital stations, and probably no LPFMs. Most of the posters here are dxers and I understand their concern. If I was an FM dxer, I wouldn't want any digital interference on the band. But then, dxers probably represent less than 1% on the radio listening public, and the needs of the entire industry need to be taken into consideration. The FCC has spoken loud and clear.

Sorry Len but I have to respectfully disagree. IBOC, especially on AM, ruins reception of the host station within its primary service area-- for no apparent benefit. I hate listening to that raspy noise on local 50,000 watt stations like 670 and 780. My solution is simple: I don't listen to those stations anymore.

When I worked in this business, people took pride in the quality of their on-air product, and they also respected their neighbors on the dial. Frankly, I can't help but wonder if radio stations are becoming dinosaurs that will be extinct before very many more years.

 

[Len14043]

Sorry Audioguy. I agree with you with respect to AM and should have specified FM in my post.

 

[audioguy]

One issue that I haven't seen much discussion about is the way that IBOC interference manifests itself -- on both AM and FM. Although the an untrained listener would not be able to classify the added hiss they hear as coming from HD radio, it is definitely much more annoying than "white noise". Although the AM version is far worse, even on FM there is a raspy "edgy" quality to the sidebands that makes it very difficult to endure from a psychoacoustic standpoint. If the interference is strong, there is also a distinct, ragged tonality to the noise. I haven't measured the frequency, but it is very bothersome.

As I was on my way home from work today, I noticed that I could readily tune in a listenable analog FM signal on every FM channel from 88.1 up through 89.7 MHz. Then I ran into the digital sidebands of Moody Radio's 100 kW IBOC-equipped signal. One could imagine that the two adjacent channels, 89.9 and 90.3, are probably totally unusable for many miles from Chicago.

The fact is that OFDM is fundamentally incompatible with analog transmission. IBOC should never have been implemented in the existing broadcast bands. Digital broadcasting would be very efficient if it were in its own, dedicated band. Of course, then we wouldn't need either IBOC or Ibiquity.

 

[TheBigA]

Of course, then we wouldn't need either IBOC or Ibiquity.

Don't blame them. They just came up with an idea that fit the FCC's agenda. If they hadn't done it, someone else would. The FCC had no logical reason to approve it, other than it allowed them to keep the status quo with regards to AM & FM, while giving the impression to Congress that they're persuing a digital program. And Congress thinks it's great, and continues to approve funding for CPB's expansion of IBOC in public radio. If the FCC was doing its job, and actually regulating the airwaves, the system would not have been approved. But the FCC has moved on to far more exciting areas of regulation, and left AM & FM to outside contractors. By the way, this isn't unique to the FCC but is rampant throughout the government.

 

[BRNout]

One issue that I haven't seen much discussion about is the way that IBOC interference manifests itself -- on both AM and FM. Although the an untrained listener would not be able to classify the added hiss they hear as coming from HD radio, it is definitely much more annoying than "white noise". Although the AM version is far worse, even on FM there is a raspy "edgy" quality to the sidebands that makes it very difficult to endure from a psychoacoustic standpoint. If the interference is strong, there is also a distinct, ragged tonality to the noise. I haven't measured the frequency, but it is very bothersome.

As I was on my way home from work today, I noticed that I could readily tune in a listenable analog FM signal on every FM channel from 88.1 up through 89.7 MHz. Then I ran into the digital sidebands of Moody Radio's 100 kW IBOC-equipped signal. One could imagine that the two adjacent channels, 89.9 and 90.3, are probably totally unusable for many miles from Chicago.

The fact is that OFDM is fundamentally incompatible with analog transmission. IBOC should never have been implemented in the existing broadcast bands. Digital broadcasting would be very efficient if it were in its own, dedicated band. Of course, then we wouldn't need either IBOC or Ibiquity.

The next time you take a drive up into southern Wisconsin (the area around Kenosha), do a bandscan and see what you get. This is normally a fantastic reception spot due to it's roughly equivalent distance from Milwaukee and Chicago, proximity to Lake Michigan (which allows the occasional MI signal to float in) and it's distance from most strong transmitters (locals WIIL 95.1 and WWDV 96.9 being the exception). Of course, I found all the above to be true with one exception: 97.1 The Drive (WDRV) from Chicago. It was literally gone. Every other Chicago FM could be received quite well, yet WDRV (with similar power and antenna height to the rest) was obliterated by hiss - HD sidebands from it's sister station WWDV 96.9 licensed to Zion, IL. Bonneville owns both stations and WWDV simulcasts WDRV's programming, so nobody is going to complain in this case. But what if that wasn't the case?

I tracked the frequency in my car and found that 97.1 was hiss and only hiss all the way through Kenosha County, WI to about 2 miles south of the IL border. From there to roughly Gurnee (about 8 mi south of the border), the sidebands and WDRV would fight it out on my system with WDRV popping in strong, then being lost for a time, etc. WWDV is a 50 kw signal, transmitting from a 486' stick located on the IL-WI border. Interestingly enough, the hiss factor wasn't equally distributed; probably because the 97.1 signal from Chicago was eventually strong enough south of the border that my radio rejected the hiss. North of the border, on the other hand, it was all hiss. And remarkably so, because other stations like WLS-FM or WBBM-FM come in just fine in this area - which was once part of the Chicago DMA (now is Milwaukee). Most Chicago signals cover Kenosha County reasonably well, truly fading once you get into the Racine area. In other words, where WDRV's signal should have still been moderately strong, it was covered over by WWDV's sidebands.

Again, to reiterate, you're not going to hear of this example because Bonneville owns them both and the 96.9 signal is a northward extension of the 97.1 signal. However, the FCC had no such thing in mind when 96.9 was originally licensed. It could have just as easily had a different owner with a different format (in fact that was the case at one time). Had that been true, you'd have WDRV being blocked out in the northern portion of it's market by the HD sidebands.

So it does happen and it will be worse once the power increase takes hold. The FCC's past short-spacing of signals will really come back to haunt everyone thanks to the way in which HD has been implemented.

 

[R.F. Burns]

I live in the NYC metropolitan area. In the 1980's onn my drive home each afternooon I'd travel for a way along the Hudson River. There was a spot where on a daily basis I could reliably receive WLNG AM on 1600 Khz in my car. WLNG was a daylight station which ran 500 watts non directional from Sag Harbor, NY. Sag Harbor is approx. 110 miles east of that location. In the meantime theer's a NYC station, WWRL which ran 5 Kw (into a 4 tower directional array). That location was in a null of WWRL and so WLNG would come through loud and clear. WLNG no longer exists on AM. It was bought out (along with a NJ station) and torn down, to allow WWRL to expand its signal by increasing it's power. the point is that no one lived in that exact location and other than a great DX location the fact that you could hear distant stations at one time from that location is irrelivant. As I've said before, I'd love it if we could go back to the old days when daytimers signed off at sunset and stations didn't run 50KW on regional frequencies. Sadly, that isn't going to happen and the increased interference is just a fact of life we have to learn to live with.

 

[Savage]

So why make it worse with IBOC? Or are we celebrating the increase in interference and wishing for more of it?

 

[Len14043]

The next time you take a drive up into southern Wisconsin (the area around Kenosha), do a bandscan and see what you get. This is normally a fantastic reception spot due to it's roughly equivalent distance from Milwaukee and Chicago, proximity to Lake Michigan (which allows the occasional MI signal to float in) and it's distance from most strong transmitters (locals WIIL 95.1 and WWDV 96.9 being the exception). Of course, I found all the above to be true with one exception: 97.1 The Drive (WDRV) from Chicago. It was literally gone. Every other Chicago FM could be received quite well, yet WDRV (with similar power and antenna height to the rest) was obliterated by hiss - HD sidebands from it's sister station WWDV 96.9 licensed to Zion, IL. Bonneville owns both stations and WWDV simulcasts WDRV's programming, so nobody is going to complain in this case. But what if that wasn't the case?

If the programming was different, that still wouldn't be an issue because Kenosha County is well outside the protected contour of WWDV. In fact, Kenosha County is located between the 40 and 50 dBm contour and is not protected at that point. See the following link:

http://radio-locator.com/cgi-bin/pat?call=WDRV&service=FM&status=L&hours=U

I tracked the frequency in my car and found that 97.1 was hiss and only hiss all the way through Kenosha County, WI to about 2 miles south of the IL border. From there to roughly Gurnee (about 8 mi south of the border), the sidebands and WDRV would fight it out on my system with WDRV popping in strong, then being lost for a time, etc. WWDV is a 50 kw signal, transmitting from a 486' stick located on the IL-WI border. Interestingly enough, the hiss factor wasn't equally distributed; probably because the 97.1 signal from Chicago was eventually strong enough south of the border that my radio rejected the hiss. North of the border, on the other hand, it was all hiss. And remarkably so, because other stations like WLS-FM or WBBM-FM come in just fine in this area - which was once part of the Chicago DMA (now is Milwaukee). Most Chicago signals cover Kenosha County reasonably well, truly fading once you get into the Racine area. In other words, where WDRV's signal should have still been moderately strong, it was covered over by WWDV's sidebands.
It could have just as easily had a different owner with a different format (in fact that was the case at one time). Had that been true, you'd have WDRV being blocked out in the northern portion of it's market by the HD sidebands.
So it does happen and it will be worse once the power increase takes hold. The FCC's past short-spacing of signals will really come back to haunt everyone thanks to the way in which HD has been implemented.

Where WDRV is affected by the digital sideband of WWDV, they would likely be affected by analog interference. You just can't hear the analog interference now because the digital signal is suppressing it due to the capture effect. You are correct when you refer to the short spacing policy of the FCC. But it is not the fault of IBOC, in that IBOC merely helps to reveal that problem.

 

[BRNout]

If the programming was different, that still wouldn't be an issue because Kenosha County is well outside the protected contour of WWDV. In fact, Kenosha County is located between the 40 and 50 dBm contour and is not protected at that point. See the following link:

http://radio-locator.com/cgi-bin/pat?call=WDRV&service=FM&status=L&hours=U

No, legally you're right, they are not within the 'protected contour' in Kenosha County. But Lake County (near Gurnee) is getting closer to that protection zone for WDRV and there was some interference there. It's becoming clear to me that some owners will push their hash right to the edge of their first-adjacent neighbor's protected 60 dbu contour. And, a lot of people listen to stations from outside of their 60 dbu contour, which is hardly generous.

Again, Bonneville programs 96.9 as a repeater of 97.1. In this case, no harm done. But the lesson here is what CAN or WILL happen elsewhere.

Where WDRV is affected by the digital sideband of WWDV, they would likely be affected by analog interference. You just can't hear the analog interference now because the digital signal is suppressing it due to the capture effect. You are correct when you refer to the short spacing policy of the FCC. But it is not the fault of IBOC, in that IBOC merely helps to reveal that problem.

With modern equipment, not nearly as much. I have radios that can easily pick out a first adjacent signal from a strong local. Particularly when that first adjacent still has a healthy signal as was the case with WDRV in that area. Not strong or local grade, but healthy. People in that area DO listen to Chicago FMs, even if the FCC has ruled that they have no right to do so.

The trouble with IBOC (and why it's different) is that you're actually lopping signal into the adjacent channel in order to make room for the entire datastream. So, out of necessity, for 96.9 to broadcast in HD, their signal has to lop into 96.7 and 97.1. When you're close enough to 96.9's transmitter site, your radio (set to 97.1) will decide to lock in on the HD sideband of 96.9 rather than the 4 or 5 out of 10 signal coming from 40 miles away. Before IBOC, it wouldn't do that until 97.1 was so weak as to lose signal or 96.9 was so strong that you would have overload. My system doesn't tend to overload like that. Remember, FM is unlike AM in that any given moment you almost always are tuned to one signal or another. Even if they cut in and out.

By the way, with the newer DSP radios, you can pull in a very weak first adjacent (even just a whisper) with a local grade sitting right there - as long as you don't have the sidebands to deal with. Mine can pull out 94.9 WOLX Baraboo, WI (150 miles from me) with local 94.7 WLS-FM right there.

Yes, technically, it's legal to have sidebands stepping all over signals that are still relatively strong and useful. But it's not good when it comes to how radio is perceived and how it serves it's audience.

 

[Len14043]

So why make it worse with IBOC? Or are we celebrating the increase in interference and wishing for more of it?

Bob, anytime a new service is added to an existing band, that causes interference for somebody. When the clear channels were broken up in the 80's and other stations were permitted to sign on to the previously channels, that caused interference to the service that existed at the time. When WYSL and other similar stations were granted a license, that caused co-channel interference to stations like WHO. Please don't get me wrong Bob, I am not begrudging you for operating your station. You are merely playing by the rules and apparently provide a good service for the Rochester area. When I travel through WNY, your station sounds like its well engineered and is pleasing to the ears. In fact, if you read some of my posts, you will see that I'm not an advocate of AM IBOC and sympathize with your situation with WBZ.

OTOH, I enjoy classical music and can appreciate the digital quieting provided by the FM system. To me, IBOC also makes my favorite FM station pleasing to the ears. Anytime a new FM station is shoehorned into the band, that causes interference. IBOC, also a new service, adds interference to the band. I am not sure whether the FM system will gain traction, but it had definitely improved my listening experience.

That is why I said interference is in the ear of the beholder. One persons livelihood may be interference to someone else, and visa versa.

 

[audioguy]

In my experience, when a new service is added (e.g. a power increase, a new facility, a night time authorization), that added service often benefits fewer listeners than the service that is taken away or seriously degraded for others. Put another way, the interference range of a radio signal far exceeds its useful service area.

Receiver technology has finally advanced to the point where listeners could have more choices and better reception with less interference than ever before-- until IBOC hash came along and negated these benefits. HD radio technology has practically taken us back to the era when FM radios had such poor selectivity that stations had to be spaced 800 kHz apart.

I like classical music too, but I'm very unhappy with the way IBOC has degraded the analog signal of my local classical station. I've heard the new "HD" signal and I don't like the way that sounds either. I'll bet Al Antlitz is turning over in his grave!

 

[DaveBayArea]

As was stated here earlier, the criteria for "protected contours" was set up many years ago. Realistically it applies to radios that have built-in 8-tracks and say "Electrophonic" on them. In addition, the criteria for spurious radiation (part 73.317) was based on the capabilities of early FM transmitters. By 1970 a typical FM transmitter was easily 40 db better than that. Now comes IBOC. At first the -20 dbc injection level was purported to meet this mask. In most cases it did. Just barely. But by this time technology had completely over-run the rules, and spurious radiation requirements should have been changed. But they weren't. WRT the digital power increase, Ibiquity's argument to the FCC now is that the spurious emission should be measured with a spectrum analyzer set to a 1 KHz bandwidth. Of course, this is voodoo science because there isn't an FM IF anywhere that is 1 KHz wide.

At the same time, "DX quality" FM receivers have become the norm. If you buy a new Lexus today they have an "FM Diversity" system that can achieve full quieting well outside the 40 dbu contour of a station. Never mind the 60. Somebody driving a Lexus and hitting a preset has no idea that they're not supposed to be listening to that station because they're outside of the protected contour. It comes in just fine if there's no IBOC interference. Without a doubt, there are far more listeners deprived of analog reception today than there are new listeners enjoying HD. I know of several people who have just quit listening to the radio because they can no longer receive their favorite station. This hurts not only that station, but others on the dial. Because they no longer switch over to a news station or another talk station. Their "radio" has become an MP3 player or web radio.

I don't understand why HD is still around, quite honestly. It doesn't sound drastically better than FM, in fact it sounds worse in some respects. The consumer acceptance (or lack thereof) is staggeringly low, and the ROI for broadcasters has to be the lowest of anything on their books. What is the purpose?

Dave B.

 

[hubcity]

I'm a bit skeptical that the FCC falls for things hook, line and sinker for long. There's an agenda playing out, and it's difficult to see what the desired end-product really is.

In terms of people not knowing they're DX-ing, that's an interesting observation. I'm sure some stations depend on that ability to bolster their service-area claims. NJ101.5 in Trenton, for instance, counts on being "all of New Jersey", even though their protected contour doesn't quite reach Newark.

But in terms of FM, tolerated interference outside the protected contour is a lot older than IBOC. My old campus station, WRSU, could be heard clearly in my hometown, until another 88.7 opened up. WFMU lost central Jersey to a new station at 91.1. A discussion of IBOC interference can't be had without also dinging the short spacing that has caused stations to lose lots of coverage, too.

So we think it's a mess. Does the FCC? No? They're the authority - change their attitude and you might get somewhere.

 

[kenglish]

So....
I've asked before. What should be done to create a Digital Audio Broadcasting service that would be acceptable?
I, personally, don't think HD Radio (IBOC) is the final goal. But, it offers some possibilities, along with some limitations.

Like someone said, above, the FCC has got to show that we're moving toward something "Digital", if only to look like broadcasters are keeping up with the times.

What's a better solution?