How noisy is it?

[DaveBayArea]

I'm in one of the "planned power outage" areas with no electricity at my house since Tuesday night. It's amazing what a portable AM radio sitting on the kitchen counter picks up when there's no electricity anywhere. I'm in Grass Valley, North of Sacramento. Found active rock on AM 1660 from Los Banos, clear as a bell from 150 miles away. Pretty much all of the Bay Area stations except ones that are covered up by locals, even KFI from Los Angeles. All of this during the day.

Dave B.

 

[crainbebo]

Absolutely. When it happens to me, I pull out the big loop and my Grundig G5 and just tune around the daytime AM dial. Noise level is so low that a few Boise AMs can be listenable in the daytime, like 580 and 670. Same with Spokane AMs and many others.
The 1660 in Merced gets out really well at night, and they have for years since Utah went defunct. On a good night, KBRE can be nulled to reveal KQWB Fargo ND underneath.

 

[wadio]

Interesting. The degradation of AM has been gradual, like the proverbial frog in boiling water. When the noise suddenly stops we see why today AM stands for Ancient Modulation.

 

[frankberry]

When I drive up to the Michigan north woods, far away from electrical noise, I've noticed that the AM reception is incredible.

 

[seattlesarchiebunker]

Absolutely. When it happens to me, I pull out the big loop and my Grundig G5 and just tune around the daytime AM dial. Noise level is so low that a few Boise AMs can be listenable in the daytime, like 580 and 670. Same with Spokane AMs and many others.
The 1660 in Merced gets out really well at night, and they have for years since Utah went defunct. On a good night, KBRE can be nulled to reveal KQWB Fargo ND underneath.

KBRE has a monster nighttime signal. Used to pick them up nightly in Seattle.

I live about 110 mi from the KBRE site. Out in the woods about 5 miles from the nearest town. It is receivable (with a decent signal) 24/7

 

[radiodx10]

Way over here in NJ, when we have a power outage, AM comes alive again. On my portable, 580 WHP from Harrisburg, PA is in like a local. Mostly all of NYC is clear, with or without electric interference. WEEU 830 Reading, PA is clear even with high QRM.

 

[FreddyE1977]

When I drive up to the Michigan north woods, far away from electrical noise, I've noticed that the AM reception is incredible.

I think ground conductivity is way better in Michigan than it is here. In general the ground there is quite swampy.
I lived halfway between Flint and Saginaw back in the day, and I could receive the old Honey Radio, way down in Monroe, at 500 watts, like it was local.

Here I used to get WKBN in Youngstown like it was local. But since they installed smart meters in the neighborhood it is virtually unlistenable.

 

[Greg Strickland]

If I'm not mistaken- Digital technology in an analog AM receiver can greatly reduce electrical interference. I don't mean going HD, but instead analog receiver noise reduction techniques using digital signal processing (DSP) of the RF system. Reduction of electrical noise in an analog modulation system is a trivial task for modern DSP.

Original perpetrator of the crime is the receiver. They threw audio under the bus, and failed to put DSP in receivers when it became available to deal with electrical noise. Furthermore, as time passed, the public and politics did not make an effort to prevent RF environment pollution from power lines and computer technology.

Obviously the information age is far more important than AM reception. Yet no effort was made.

 

[kevtronics]

If I'm not mistaken- Digital technology in an analog AM receiver can greatly reduce electrical interference. I don't mean going HD, but instead analog receiver noise reduction techniques using digital signal processing (DSP) of the RF system. Reduction of electrical noise in an analog modulation system is a trivial task for modern DSP.

AMAX-certified receivers were doing that back in the '90s with analog technology: noise blanking and Dynamic Noise Reduction (DNR).

A decade ago I had a car whose radio had noise blanking on AM and it worked very well. When I drove under a noisy power line, instead of buzzing and crackling, the audio just got distorted. It remained intelligible unless the noise was so bad that the blanking was nearly constant.

These days most car radios are DSP-based, which means adding features like noise blanking, DNR, variable bandwidth, and even C-Quam AM Stereo would be trivial, if only they cared enough about it.

I drove a 2018 Jeep recently and its factory radio has very noticeable automatic bandwidth on AM -- it sounded like it ranged from around 4 kHz on weak signals to around 8 kHz on the strongest ones. But it also sounded very shrill, like the audio response is flat to the cutoff point, with no de-emphasis. I guess whoever designed it never heard of the NRSC curve?

 

[boombox4]

If I'm not mistaken- Digital technology in an analog AM receiver can greatly reduce electrical interference. I don't mean going HD, but instead analog receiver noise reduction techniques using digital signal processing (DSP) of the RF system. Reduction of electrical noise in an analog modulation system is a trivial task for modern DSP.

Original perpetrator of the crime is the receiver. They threw audio under the bus, and failed to put DSP in receivers when it became available to deal with electrical noise. Furthermore, as time passed, the public and politics did not make an effort to prevent RF environment pollution from power lines and computer technology.

Obviously the information age is far more important than AM reception. Yet no effort was made.

DSP has been in a large percentage of MW radio receivers for at least the past 7-8 years (longer in car radios, probably). My Sangean PR-D5 is a DSP model, and they took that model from PLL to DSP in 2012, so I'm using that year as a sort of transition year, as Sangean is a fairly large portable radio manufacturer.

DSP doesn't eliminate noise. My three DSP MW radios all receive noise. DSP can reduce noise, but I've got PLL / analog radios that are just as 'noise-free' as my DSP radios. Some of my own PLL and analog tuned MW radios are more prone to amplify noise than others.

As the poster above me mentions, there were noise reduction circuits in analog radios before DSP came out. The problem is that some noise simply can not be completely eliminated.

The problem isn't the receivers, when it comes to noise. The problem is the noise. The problem with receivers is many of them have reduced bandwidth from AM radios 50 years ago. It was apparently part of a standard set in the 1980's, and receiver manufacturers followed. Also, some portables have reduced bandwidth because it reduces interference from nearby strong signals.

 

[vchimpanzee]

A decade ago I had a car whose radio had noise blanking on AM and it worked very well. When I drove under a noisy power line, instead of buzzing and crackling, the audio just got distorted. It remained intelligible unless the noise was so bad that the blanking was nearly constant.

My grandfather's 1978 Malibu must have had something like that. Unfortunately, the range of most AM stations was about like those stations that were allowed to have a nighttime signal after being daytime-only for most of their history.

 

[kevtronics]

The problem isn't the receivers, when it comes to noise. The problem is the noise. The problem with receivers is many of them have reduced bandwidth from AM radios 50 years ago. It was apparently part of a standard set in the 1980's, and receiver manufacturers followed. Also, some portables have reduced bandwidth because it reduces interference from nearby strong signals.

Not any standard that I know of, but rather the increasing use of ceramic filters in AM tuners in the '80s, rather than the slug-tuned coils in older radios that let more high frequencies come through. Many AM stations were using excessive pre-emphasis to improve the sound of older AM radios, but this just ended up causing more interference and distortion with the newer ceramic filter tuners.

The NRSC curve was meant to get AM stations to back off to a more reasonable amount of pre-emphasis, and more importantly to establish a standard that receiver manufacturers could follow (just like the 75 µS curve on FM), but the FCC never made it mandatory for mono AM stations (only AM Stereo stations were required to use it), so most receiver manufacturers ignored it and just kept on making narrowband radios.

 

[davideduardo]

Not any standard that I know of, but rather the increasing use of ceramic filters in AM tuners in the '80s,

The NRSC 10 kHz "hard wall" for AM audio bandwidth was intended to reduce adjacent channel interference, and caused manufacturers to adopt much narrower AM bandwidth standards for receivers.

rather than the slug-tuned coils in older radios that let more high frequencies come through. Many AM stations were using excessive pre-emphasis to improve the sound of older AM radios, but this just ended up causing more interference and distortion with the newer ceramic filter tuners.

I've never hear the term "pre-emphasis used in the context of AM analog audio except in the never-implemented 1985 NRSC voluntary standards "suggestion".

What stations were doing is, starting in the mid- to late-70's, employing multiband processing and trying to sharpen the sound. But that effort dates back even to the CBS Labs Dynamic Presence Equalizer which came out in the late 60's and was essentially a content-controlled EQ that attempted to keep the "presence band" audio as high as possible.

The NRSC curve was meant to get AM stations to back off to a more reasonable amount of pre-emphasis, and more importantly to establish a standard that receiver manufacturers could follow (just like the 75 µS curve on FM), but the FCC never made it mandatory for mono AM stations (only AM Stereo stations were required to use it), so most receiver manufacturers ignored it and just kept on making narrowband radios.

The NRSC is really not a curve and its purpose is not as stated. The original 1985 standard talked about a pre-emphasis and de-emphasis aspect, but that was never widely adopted by radio. But the part of the 1985 "findings" that established 10 kHz as AM bandwidth is employed by nearly every station today.

The NRSC AM standard is a brick wall, intended to keep stations on adjacent channels from interfering. Radios were already pretty narrow-banded as witnessed by the NRSC committee headed by Bob Orban that looked at the state of consumer radios prior to the introduction of HD Radio: the average consumer radio, including those made recently and those of the last several decades, started rolling off at around 4 kHz (3.9 kHz was, IIRC, the roll point the committee specifically mentioned) and none rolled off any later than about 5 kHz.

The real reason the quality of the AM sections of radios declined beginning in the 90's is what I've heard called the "WalMart effect" which is the result of mass retailers putting pressure on the price of goods purchased. It was realized that AM had ceased to be a music medium and, thus, the quality of the AM tuner in AM/FM radios could be cut, saving a penny or two per unit. Consumers would not notice, as nobody was using AM radios for music except, perhaps, seniors, and the effects of aging made that a moot point.

 

[Greg Strickland]

boombox4- When you say DSP model, what do you mean?
kevtronics- I'd like to hear a modern AM radio such as the Jeep model you mentioned. Sounds interesting.
I heard a Ford Escape AM radio in the 90's that was good enough to hear tape noise (or something like it) on KFWB news actualities.
I remember hearing ceramic IF filters in car AM radios in the '80s. It was awful, total cut off somewhere between 3 and 5 KHz.

About NRSC- I recall primary purpose of it was the cut off just above 9 KHz. The pre-emphasis increased to about 10 dB before the cut off. I don't recommend thinking too hard about NRSC curve.

My opinion- much of the audio sound of AM stations I hear is more about their self-inflicted audio processing choices. And they want to be saved...

 

[boombox4]

boombox4- When you say DSP model, what do you mean?

Greg, I mean that the IF chip inside the radio is not a standard, analog IF chip. It's a DSP chip, a digital processor -- like the SiLabs series, and other manufacturers, where the chip that runs the radio circuitry is software based, rather than a chip full of oscillators, filters, diodes, etc.

More and more portables are going DSP. There is one chip that runs the radio, and another chip that merely amplifies the audio output to run a speaker or headphones. Usually there is a third chip (a microprocessor) that operates the whole thing.

The Sangean PR-D5, which I mentioned, used to have a PLL, analog system, much like the SW multiband, digitally tuned radios of the 80's-00's -- a chip to amplify FM, a chip that ran the tuning and radio functions (clock, memories, buttons, etc.), and an IF chip that amplified and filtered the RF and turned it into audio -- then, an audio chip usually followed, that ran the speakers. Bandwidth on such radios was accomplished by coils or ceramic filters (usually a combination of both).

With DSP chips, all you need is a chip for the radio processing, a chip to boost the audio into a speaker, and a microprocessor chip to run the tuning, clock, and buttons, etc.

PS -- not all ceramic filtered radios sounded bad. It depended on the filter, and how the rest of the radio was set up.

 

[Greg Strickland]

Greg, I mean that the IF chip inside the radio is not a standard, analog IF chip. It's a DSP chip, a digital processor -- like the SiLabs series, and other manufacturers, where the chip that runs the radio circuitry is software based, rather than a chip full of oscillators, filters, diodes, etc.

Thank you boombox4, that is very interesting.

To David's point- FCC rule 73.44 specifies emission limitations. I think with a modern audio processor/transmitter/antenna system, AM station should be able to comply with the rule. NRSC-1-CNRSC AM Preemphasis/ Deemphasis and Broadcast Audio Transmission Bandwidth Specifications April, 2018 is available on Internet. I've heard some AM stations splattering like it's 1975. I've also heard Class A 50 KW AM stations that were clearly and obviously in compliance, and sounding good.

Best wishes to all.

 

[Kelly A]

The Orban 9100 audio processors used to come with two preemphasis boards which consisted of a small resistor network. This would allow stations running a 9100 processor either a 75 microsecond or 150 microsecond audio preemphasis in the processing chain. When the digital versions came out, preemphasis could be turned on or off in the software. In both vintages, the 10Khz low pass filter is built in to comply with US NRSC standards.

 

[davideduardo]

Thank you boombox4, that is very interesting.

To David's point- FCC rule 73.44 specifies emission limitations. I think with a modern audio processor/transmitter/antenna system, AM station should be able to comply with the rule. NRSC-1-CNRSC AM Preemphasis/ Deemphasis and Broadcast Audio Transmission Bandwidth Specifications April, 2018 is available on Internet. I've heard some AM stations splattering like it's 1975. I've also heard Class A 50 KW AM stations that were clearly and obviously in compliance, and sounding good.
.

I think for this discussion it's important to separate the preemphasis issue from the bandwidth one.

You mention 73.44 which requires a 25 db reduction at 10.2 kHz, which is, IIRC, less strict than the NRSC standard but has essentially the same goal of putting a had wall at 10 kHz to prevent adjacent channel interference.

Since the rest of the NRSC plan, the preemphasis/deemphasis part, depended on receiver manufacturer cooperation by incorporating the curve in new radios, that part is essentially dead or voluntary on the station end.

I don't recall whether any receivers were made using the receiver based deemphasis specification.

 

[kevtronics]

The NRSC 10 kHz "hard wall" for AM audio bandwidth was intended to reduce adjacent channel interference, and caused manufacturers to adopt much narrower AM bandwidth standards for receivers.

If any did, then that was the exact opposite of the intended results! The whole point of it was to encourage receiver manufacturers to increase their AM audio bandwidth (up to 10 kHz), now that second-adjacent channel stations were no longer splattering onto each other.

I've never hear the term "pre-emphasis used in the context of AM analog audio except in the never-implemented 1985 NRSC voluntary standards "suggestion".

Although it was voluntary, the NRSC claimed that as of 1989, over 1000 stations had adopted their recommended "modified 75 uS" AM pre-emphasis curve. Many stations added the Inovonics 222 processor as a cheap way to make their audio NRSC-compliant. The NRSC curve was eventually made mandatory for AM Stereo stations when the FCC finally chose C-Quam as the single standard in 1993, and for all AM stations (mono or stereo) in Canada.

Radios were already pretty narrow-banded as witnessed by the NRSC committee headed by Bob Orban that looked at the state of consumer radios prior to the introduction of HD Radio: the average consumer radio, including those made recently and those of the last several decades, started rolling off at around 4 kHz (3.9 kHz was, IIRC, the roll point the committee specifically mentioned) and none rolled off any later than about 5 kHz.

I believe you're quoting a study of AM receiver bandwidths done by iBiquity as part of their justification for narrowing the analog audio bandwidth to 5 kHz on AM IBOC stations. But the sneaky thing they did was employ that 5 kHz brickwall filter on the transmitter they were using during the test, so of course the results showed that no radio they tested had any response above 5 kHz! They also further skewed the results by purposely switching a Delco car radio and GE Superadio III they tested into narrow bandwidth mode, instead of wideband mode.

A few years later the NRSC did another test of AM audio bandwidths on various receivers, without any such shenanigans, and concluded that narrowing the transmitted audio bandwidth to any less than 7 kHz would cause the received audio quality to be unacceptably degraded, even on typical modern AM radio tuners.

Nowadays in the NYC area, most AM stations are using an audio bandwidth of at least 8 kHz, even on the few that are transmitting IBOC. This is noticeably increased compared to a decade ago when iBiquity tried to convince everyone that 5 kHz was the way to go.

 

[davideduardo]

If any did, then that was the exact opposite of the intended results! The whole point of it was to encourage receiver manufacturers to increase their AM audio bandwidth (up to 10 kHz), now that second-adjacent channel stations were no longer splattering onto each other.

And that really only mattered if AM stations were still playing lots of music. But AM lost it's music majority to FM around 1975 and continued to decline each year after that.

Manufacturers understood how radios were used, and realized that AM was only interesting as a talk medium

The NRSC curve was eventually made mandatory for AM Stereo stations when the FCC finally chose C-Quam as the single standard in 1993, and for all AM stations (mono or stereo) in Canada.

But C-Quam was never a success, particularly at the receiver end.

I believe you're quoting a study of AM receiver bandwidths done by iBiquity as part of their justification for narrowing the analog audio bandwidth to 5 kHz on AM IBOC stations.

No, I am quoting the NRSC group headed by Bob Orban which looked at AM receiver bandwidth. It was presented at one of the NAB engineering seminars that accompany the convention each year. A wide variety of off the shelf receivers were tested using a flat transmission system and test tones.

A few years later the NRSC did another test of AM audio bandwidths on various receivers, without any such shenanigans, and concluded that narrowing the transmitted audio bandwidth to any less than 7 kHz would cause the received audio quality to be unacceptably degraded, even on typical modern AM radio tuners.

I can't find the study although it is likely in one of my NAB Engineering books. The conclusion I remember is that all receivers started to roll at around 3800 Hz and most were essentially dead by 5000 Hz with a few having well attenuated response up to 7000 Hz.

This was around the time that Clear Channel tested limiting bandwidth of HD stations to 6 kHz and found it worked fine.

Nowadays in the NYC area, most AM stations are using an audio bandwidth of at least 8 kHz, even on the few that are transmitting IBOC. This is noticeably increased compared to a decade ago when iBiquity tried to convince everyone that 5 kHz was the way to go.

No, iBiquity issued a paper after the Clear Channel tests showing that 6 kHz could be employed in certain cases. The argument was that many directional systems with high-Q tuning could not deal with HD and 6 kHz audio at the same time. But the, they could not deal with analog audio above about 5 kHz to 6 kHz very well anyway.

You are forgetting that most directional systems built before the late 70's or early 80's and which were not redesigned later had a real hard time passing high fidelity audio of any kind.