The Day the AM Band Died

[awj223]

If there has been no significant daytime interference, why would there be any at night? Since AM listening is much, much lower at night, the number of potential complainers would be significantly less.

Skywave interferes with groundwave? In case you haven't noticed, the AM band is a lot busier at night even with analog only. Have you never tuned through the band at night? Have you ever taken a spectrum analyzer and looked at the AM band at night vs. during the day? Maybe you've never tuned to a frequency at night and heard the beat from 3 or more carriers slightly at slightly different frequencies. Don't you, or anybody at the FCC for that matter, understand that noise is additive?

Also if there is so little AM listening at night, why should HD need to be kept on? Almost nobody is going to notice the lack of hybrid HD on AM at night since according to you almost nobody is listening in the first place.

In other words, it is not a DC station. It is at best, a Montgomery County, MD, station.

No station is protected against interference in the area where, in theier dreams, they would like to cover.

Agree. FCC policy has to do with protected contours and nothing to do with reported listening. The FCC won't shut down a station even if it has 0 reported listeners. However...

And that station is inside the metro. Arlington is part of the DC market.

A top 10 station in Santa Barbara, CA was KLVE from LA. The FCC licensed a new staiton in Santa Barbara (the market, not the city) on the adjacent channel. Now you can not get KLVE anyplace int he county. It was nice while it existed, but there was no guarantee of future service.

Compare to:

There is scant evidence that HD would interrupt any significant amount of listening in fringe areas, as there is not much listening to fringe signals at all, on AM or FM.

Okay Mr. Eduardo, KLVE doesn't even put 50 dBu anywhere into that county, and you say what? It made the top 10? How can that be, since there is hardly any fringe listening on either band? What is false, the Arbitron diary reports, or your claims about fringe listening?

 

[SUPERCASTER]

Eduardo falsely proclaimed again::

If there has been no significant daytime interference, why would there be any at night?

Wrong as usual.
WDAS 1480 AM HD buzzes on WBCB 1490 AM within the 1 mv/m daytime coverage area. At night it will get better?
Perhaps for WDAS, but not for WBCB.
With all current FCC frequency assignments (AM or FM) tightly based on each station occupying one channel and not 3 or 5, how can you conclusively proclaim there will be no harm, anywhere, day or night?
You can't honestly make any such statement. You are just deep in denial.

 

[R.F. Burns]

Eduardo falsely proclaimed again::

If there has been no significant daytime interference, why would there be any at night?

Wrong as usual.
WDAS 1480 AM HD buzzes on WBCB 1490 AM within the 1 mv/m daytime coverage area. At night it will get better?
Perhaps for WDAS, but not for WBCB.
With all current FCC frequency assignments (AM or FM) tightly based on each station occupying one channel and not 3 or 5, how can you conclusively proclaim there will be no harm, anywhere, day or night?
You can't honestly make any such statement. You are just deep in denial.

Take a look at the WDAS pattern. Although not a sharp null, Trenton is in a null of the WDAS signal. If WBCB finds interference within their protected contour on their frequency, whihch happens to be a local channel, then they should take legal action. If not, they are out of luck.

 

[Tom Wells]

Even with as much interference as I have witnessed on first adjacent channels from HD Radio signals, and (very much depending on the receiver) some interference to much weaker second-adjacent channels, I find it hard to believe that any significant number of receivers whatsoever have issues on third-adjacent channels. I have only one receiver that is really REALLY wideband, which gives me the "waterfall" on any HD station, and even on that receiver, it has no issues 30kHz away from an HD station. Coincidentally, that receiver is so wideband that is sounds "nice" only for the absolute strongest stations. Any moderate or weaker stations sound awful on it, IBOC or not.

In both of my cars (stock Nissan, and after-market Blaupunkt Alaska-II), I can listen to 700 WLW Cincinnati, which is barely audible at all during the day, as I drive past the 720 WGN Chicago tower. I lose WLW within a mile of the tower, not because of IBOC, but simply because of desensitization. 710 and 730 are a solid, loud hash, but 700 WLW has no more background noise than a station 275 miles away normally would. It would also be a safe bet that virtually nobody at all is listening to WLW Cincinnati in the Chicagoland area during the day.

So far I have found all your comments reasonable, but I can't accept the situation you describe as authentic.

I suspect you are not truthful here or have 2 magic radios.
I favor an old blaupunkt Richmond I have in one car, but it wouldn't be able to slice what you've described.

I work 2 miles from the site you mention. You should also mention WBBM 780 is in IBOC only 1/2 mile away, and WSCR 670 in IBOC is only 3-4 miles from this same spot.

I agree that 3rd adjacents have no problem, as I can hear WNDZ 750 just fine between WGN 720 and WBBM 780, both IBOC.
This same radio with a TRF AM input, which I can listen to any 2nd analog adjacent just fine, and many firsts, is unable to get even a muddy whiff of WLW anywhere in the Chicago area with WGN on IBOC. And WLW was a usable signal as you state.
The overload effect is truly great within a one-mile area, but beyond that, proper radios are selective enough.

I am currently 25 miles SW of WGN, and no vestige of WLW is present.
WGN's sidebands meet WSCR's sidebands, and to a continuous-tuned consumer grade radio,
a band of strong hiss fills the hole where I used to be able to listen to WLW.

WMT 600 in Iowa is coming in strong, so daytime propogation is good.
WTMJ 620 in Milwaukee is throwing a strong hiss into WMT.

If WGN is not putting HD sidebands down to 706.? khz, then they're not in HD.
These sidebands would decode against WLW as hiss from 6 khz and up.

I will be checking this tomorrow on a radio with narrow selectivity and a loop antenna.

 

[PhilJSmith67]

I suspect you are not truthful here or have 2 magic radios.

I highly doubt they are magic. I can also cite your example of being able to listen to WMT on either receiver with no background noise above normal due to WTMJ. When WIND ran IBOC until last year, which is only 17 miles from my house, I was able to listen to 580 WILL Urbana on either radio with no problems whatsoever. My receivers in the house were a different story, but in the car, WILL was as clear as it is today.

It was early in the day (but definitely "daytime") when I experimented with WLW. I believe that WLW already had their IBOC signal on, but that didn't make a difference. I travelled I-290 past Woodfield without any "abnormal" reception issues, other than the desensitization that I expected. If there was any hiss from the IBOC signal of WGN, it was not discernable from the background noise and hiss already there.

 

[davideduardo]

Skywave interferes with groundwave? In case you haven't noticed, the AM band is a lot busier at night even with analog only. Have you never tuned through the band at night?

Yeah, but this generally does not affect local signals of listenable intensity. Of course, situations like heavy aurora conditions in the north are among the exceptions.

Have you ever taken a spectrum analyzer and looked at the AM band at night vs. during the day?

Yeah, again. One of my DX receivers (TenTec 350) has a built in spectrum analyzer.

Maybe you've never tuned to a frequency at night and heard the beat from 3 or more carriers slightly at slightly different frequencies.

Except for rare difficulties in frequency control, this does not affect US stations. The FCC tolerance is below most human's ability to hear (generally much less than 20 Hz, the limit of +/- 10 Hz)

Don't you, or anybody at the FCC for that matter, understand that noise is additive?

The issue is that this is not a problem inside the usable signal areas of AMs today.

Also if there is so little AM listening at night, why should HD need to be kept on? Almost nobody is going to notice the lack of hybrid HD on AM at night since according to you almost nobody is listening in the first place.

I said night radio listening is about a quarter of the daytime (6 AM to 7 PM ) level. However, the time is important, as that is where stations run most of the bonus spots they use to compete for ad buys.

A top 10 station in Santa Barbara, CA was KLVE from LA. The FCC licensed a new staiton in Santa Barbara (the market, not the city) on the adjacent channel. Now you can not get KLVE anyplace int he county. It was nice while it existed, but there was no guarantee of future service.

Compare to:

There is scant evidence that HD would interrupt any significant amount of listening in fringe areas, as there is not much listening to fringe signals at all, on AM or FM.

Okay Mr. Eduardo, KLVE doesn't even put 50 dBu anywhere into that county, and you say what? It made the top 10? How can that be, since there is hardly any fringe listening on either band? What is false, the Arbitron diary reports, or your claims about fringe listening?

Actually, grandfathered KLVE does put a 50 over much of the market (it gets a 60 into the southern piece, in fact), but it is only FCC protected to the extent of the conforming Class B coverage, so the added coverage is not guaranteed.

My KLVE example was intended to show that "out of primary" coverage is not protected, even if listeners can use the signal. The reason why KLVE 107.5 can no longer be heard is a new 107.7 B in the market, which obliterates the distant signal, even if it approaches listenable level. In the case of HD, the separations are greater than this case. Again, the FCC does not protect beyond the protected contours, and the same applies to HD... as long as protected contours are not affected there is no issue.

In LA, 103.5 and 103.9 both are HD, and cause no interference.

 

[awj223]

Except for rare difficulties in frequency control, this does not affect US stations. The FCC tolerance is below most human's ability to hear (generally much less than 20 Hz, the limit of +/- 10 Hz)

I can hear a 1 Hz difference in carriers. It doesn't sound like a 1 Hz tone, but rather like someone is jerking the volume control knob up and down with a frequency of 1 Hz. Most of the stations I hear interfering in this way differ by about 2-4 Hz.

Actually, grandfathered KLVE does put a 50 over much of the market (it gets a 60 into the southern piece, in fact), but it is only FCC protected to the extent of the conforming Class B coverage, so the added coverage is not guaranteed.

What maps are you using to make this claim? Both the FCC 54 dBu maps and the radio-locator maps show that 50 dBu does NOT reach into Santa Barbara county.

http://www.fcc.gov/fcc-bin/FMTV-service-area?x=FM210350.html
http://radio-locator.com/cgi-bin/pat?call=KLVE&service=FM&status=L&hours=U

The county boundary is about 15-20 miles west of Oxnard/Ventura.

My KLVE example was intended to show that "out of primary" coverage is not protected, even if listeners can use the signal. The reason why KLVE 107.5 can no longer be heard is a new 107.7 B in the market, which obliterates the distant signal, even if it approaches listenable level. In the case of HD, the separations are greater than this case. Again, the FCC does not protect beyond the protected contours, and the same applies to HD... as long as protected contours are not affected there is no issue.

I already agreed with you on this point. The FCC cares about protected contours, not listeners. I was simply pointing out that you first argued that listening outside the protected contours is so low that it doesn't even show up in diary returns, then turned around and stated that KLVE was making the top 10 in a market where it's considered a fringe signal. Therefore, there IS still fringe listening that is being affected by HD radio. Not that the FCC cares, as it has never been their policy to protect these signals, listening or not. I could argue something about the stupidity of using a NRSC mask developed as a worst case boundary for the worst out-of-channel polluters as a digital modulation mask, but that is another discussion.

 

[davideduardo]

I can hear a 1 Hz difference in carriers. It doesn't sound like a 1 Hz tone, but rather like someone is jerking the volume control knob up and down with a frequency of 1 Hz. Most of the stations I hear interfering in this way differ by about 2-4 Hz.

How can you hear something that is subaudible. Even 25 Hz cue tones on old automation tapes in the 70's could not be heard by most of the population (although if not pure, you heard the harmonic). "The general range of hearing for young people is 20 Hz to 20 kHz."

"The general range of hearing for young people is 20 Hz to 20 kHz."

What maps are you using to make this claim?

Langley Rice calculations and actual measurement. The FCC map is for protection, not of real coverage, as you should know. Radio Locator does not lable its contours, and they are "for amusement purposes only."

Both the FCC 54 dBu maps and the radio-locator maps show that 50 dBu does NOT reach into Santa Barbara county.

The real 60 hits the county line and the 54 vovers the bulk of the HISPANIC population of the market, which is not evenly distributed.

I already agreed with you on this point. The FCC cares about protected contours, not listeners. I was simply pointing out that you first argued that listening outside the protected contours is so low that it doesn't even show up in diary returns, then turned around and stated that KLVE was making the top 10 in a market where it's considered a fringe signal. Therefore, there IS still fringe listening that is being affected by HD radio. Not that the FCC cares, as it has never been their policy to protect these signals, listening or not. I could argue something about the stupidity of using a NRSC mask developed as a worst case boundary for the worst out-of-channel polluters as a digital modulation mask, but that is another discussion.

KLVE is the rare example of a superpower grandfathered station, which makes it an exception rarely duplicated to this extent (29 kw on top of a 5100 mountain where the radiation towards populated areas takes full advantage of this height. that is why I used it to show really usable coverage that the FCC does not protect.

 

[Mike Walker]

awj223 asks "How can you hear something that is subaudible. Even 25 Hz cue tones on old automation tapes in the 70's could not be heard by most of the population (although if not pure, you heard the harmonic). "The general range of hearing for young people is 20 Hz to 20 kHz."


25hz was considered "subaudible" because most speakers and radios didn't go that low, not because hearing didn't. Some pipe organs have a pipe tuned to 16hz!

The truth is, anything much below 30hz is VERY difficult to reproduce in a real room because of standing waves, the distance required for cone excursions, cabinet tuning in anything approaching a "reasonable" size, etc. But today there are more and more systems that actually go that low...and it's interesting what we hear. Like "sub-audible tones".

By the way...I could ALWAYS hear them (at stations I've worked at through the decades) through headphones. And they sure rattled cue speakers, didn't they guys?

By the way a)-it's high frequency hearing that we lose with age, not low frequency...and b)-I hate to point this out...but 25hz is within the "20-20khz" range. Duh!

 

[R.F. Burns]

awj223 asks "How can you hear something that is subaudible. Even 25 Hz cue tones on old automation tapes in the 70's could not be heard by most of the population (although if not pure, you heard the harmonic). "The general range of hearing for young people is 20 Hz to 20 kHz."


25hz was considered "subaudible" because most speakers and radios didn't go that low, not because hearing didn't. Some pipe organs have a pipe tuned to 16hz!

The truth is, anything much below 30hz is VERY difficult to reproduce in a real room because of standing waves, the distance required for cone excursions, cabinet tuning in anything approaching a "reasonable" size, etc. But today there are more and more systems that actually go that low...and it's interesting what we hear. Like "sub-audible tones".

By the way...I could ALWAYS hear them (at stations I've worked at through the decades) through headphones. And they sure rattled cue speakers, didn't they guys?

By the way a)-it's high frequency hearing that we lose with age, not low frequency...and b)-I hate to point this out...but 25hz is within the "20-20khz" range. Duh!

But theoretically in a properly set up facility those tones should be filtered. The way the encoders works is that unless the 25 Hz button is depressed the unit acts as a notch filter to prevent false cues from triggering a stations automation. The same notch should be in place at a stations decoder. the 25 Hz (and 35 Hz) tones should trigger automation but not pass to their air chain. Actually, the 25 Hz tone has to be decoded prior to any processing which will effect the tone's level. When it comes to cart tone, 1 K is used for the primary/cuing function, 150 Hz for the secondary tone, activating a 3rd party device, & 8 KHz for the tertiary cue. The reason you might hear these tones on the air is due to poor head alignment. The tones are on a separate track and if the head isn't aligned perfectly it will also play the tones as part of the program output.

 

[amfmsw]

For the love of God, someone explain to this person what a "beat" is. You keep comparing it to audio. It's an RF beat, causing their modulated audio to oscillate...oh never mind...it's too frustrating.

 

[rbrucecarter5]

Maybe that warbling sound I notice on IBOC AM stations (probably due to sideband assymetry), classifies as an RF beat. It sounds like a BFO on a communications receiver. Just one more way the AM IBOC system fails.

 

[Mike Walker]

You're right RF...the tones "should have been filtered". Except that "filtering" would mean chopping off all audio below what...40hz? 50hz? NOT EXACTLY HIGH FIDELITY! I know everybody did it, but everybody was WRONG! There's no reason FM, or AM for that matter can't extend bass into the "bassment". Imagine an automated classical station playing organ music, with "properly filtered" audio...NO PEDAL TONES! LF fundamentals from string basses? GONE! The viscernal "whomp" from the big bass drum on Telarc recordings? GONE! NOT HIGH FIDELITY, and certainly not good 21st century engineering!

There's PLENTY of lf information below 40hz these days! CLEAN AUDIO means broadcasting what's on the recording. Stepping off soapbox now.

(I know, one could filter LF tones from network audio, but not from other sources, but still...

 

[Chuck]

You're right RF...the tones "should have been filtered". Except that "filtering" would mean chopping off all audio below what...40hz? 50hz? NOT EXACTLY HIGH FIDELITY! I know everybody did it, but everybody was WRONG! There's no reason FM, or AM for that matter can't extend bass into the "bassment". Imagine an automated classical station playing organ music, with "properly filtered" audio...NO PEDAL TONES! LF fundamentals from string basses? GONE! The viscernal "whomp" from the big bass drum on Telarc recordings? GONE! NOT HIGH FIDELITY, and certainly not good 21st century engineering!

There's PLENTY of lf information below 40hz these days! CLEAN AUDIO means broadcasting what's on the recording. Stepping off soapbox now.

(I know, one could filter LF tones from network audio, but not from other sources, but still...

Back in the days when those sub-audible tones were very common in radio, people were still using vinyl records. It's true that you can get some very low frequencies on a vinyl record, if you don't mind how wide the groove gets. That means you don't get as much time on a single side of a record. For purely practical reasons (we'd like to get 6 songs on the side of an album) most recordings simply did not go that low. 40 Hz was about it. The master tape may have contained frequencies below that, but in the disk cutting process, the mastering engineer would intentionally roll off the extreme low end. A good mastering engineer was a true artist, getting as much out of the process as he could.

I'll submit that there are lots of really great recordings that meet my criteria for "High Fidelity" and they have absolutely nothing below 40 Hz. A lot of what passes as "21st century engineering" is absolute crap compared to many of those recordings. And no, I'm not one of those "vinyl is better" guys. It's just that in many cases, we seem to have substituted technology for artistry.

 

[awj223]

How can you hear something that is subaudible. Even 25 Hz cue tones on old automation tapes in the 70's could not be heard by most of the population (although if not pure, you heard the harmonic). "The general range of hearing for young people is 20 Hz to 20 kHz."

I never claimed to be able to hear tones below 20 Hz. What I said is that two stations on the same channel, by transmitting at carrier frequencies f1 and f2 (where f1 and f2 differ by a few Hz), causes the volume of the demodulated signal to oscillate with a frequency abs(f1-f2). At least, that's what I think is happening. If the two carriers are close in strength, if you look at them in the time domain they're going to go from periods of near perfect destructive interference to near perfect constructive interference and back again with a frequency abs(f1-f2). I believe this is what causes the oscillations in volume. Constructive interference makes the output from the speakers loud, but when the signals interfere destructively the volume drops to almost nothing. While you can't hear a 4 Hz pure tone, you can certainly notice when the volume oscillates up and down 4 times per second.

 

[Tom Wells]

I have tested the WGN-WLW issue as find the following:

Everything is exactly as reported by Phillip J. Smith until the moment of WGN IBOC start-up.
WLW sounds just like it ever has, exactly as strong +/- small amount.

WLW, being approximately 140 miles east of WGN, has an earlier local sunrise.
Their IBOC sidebands were audible but falling into WGN's splash.

After IBOC sign on at WGN, only my Sangean 803 in narrow mode can prove WLW is still there by
turning on the BFO, but no positional nulling with the loop helps, nor does any fiddling
with audio.

These tests (except IBOC-on moment) were repeated at 20, 10, and 2 miles due east of WGN.

WMT 600 is strong today.
So is the hiss from WTMJ.

I am suprised you say the hiss from WTMJ is not evident, Phillip. Perhaps not on the car radios.
They sound to be as narrow as communication receivers.
Does either one have continuous tuning?

It is posssible to listen to the lower sidebands of WMT to avoid the hiss of WTMJ.
But center tuning of WMT yields an objectional intermodulation with WTMJ's lower digital sidebands.

I would happily record these tests if anyone doubts this anecdotal data.

 

[davideduardo]

You're right RF...the tones "should have been filtered". Except that "filtering" would mean chopping off all audio below what...40hz? 50hz?

Actually, they were very sharp notch filters that specifically eliminated 25 Hz and nothing else. The bandwidth was a couple of HZ at most.

 

[Mike Walker]

Most traditional rock has nothing much below 40hz (by "traditional" I mean four piece...bass, drums, lead and rhythm guitar). The lowest tone in such an ensemble would likely be the 42hz open e string on the bass. Add keyboards, and there's plenty of potential for stuff below 40hz.

From the time syntheseizers became common in the early 70s, "plumbing the depths" became common as well. For every recording you could name with nothing below 40hz, I could name one with PLENTY. Yes, bass takes up more room, and lowers playing time. There were many ways of dealing with this. One was to simply lower the overall level. Remember...even if you do have extended bass, that doesn't necessarily mean LOUD bass (there's a difference!), and just because there are notes in the very bottom octave doesn't mean they are there all the time. Music isn't pure sine waves (of course). LPs DID, and DO have content below 40hz.

I agree that engineering in the digital age has gotten largely AWFUL. Most hit cds look like pure square waves on an oscilloscope. VERY SAD. No dynamic range at all, with every peak clipped. BUT there are many well engineered recordings out there, and when the engineer actually knows what he/she is doing, today's gear is capable of extension down to dc. Hell, with digital transmission, it's actually possible to BROADCAST dc. Which of course isn't sound at all, but still

You say there are plenty of LPs with nothing below 40hz that are high fidelity. Of course you're right. BUT, if the content WAS THERE, and didn't make it to the recording, or is on the recording but isn't brodcast, then by definition it isn't high fidelity.

 

[Mike Walker]

Of course DaveEduardo, a notch filter that sharp produces some pretty severe phase shift in the spectrum surrounding it. But your point is well taken.

Today I guess it would be possible to do something like the pilot cancelling in some tuners...phase locking to the tone, producing one of equal amplitude but reversed polarity, and cancelling it with no filtration.

 

[R.F. Burns]

You're right RF...the tones "should have been filtered". Except that "filtering" would mean chopping off all audio below what...40hz? 50hz?

Actually, they were very sharp notch filters that specifically eliminated 25 Hz and nothing else. The bandwidth was a couple of HZ at most.

Exactly right David. I thought that's what I said. The problem is that in stations where maint. isn't all the important electronics drift and so you can hear the tones on the air. the tones might be sent at 0 or +4 and so after processing even a little tone leakage can be heard.