AM receiver frequency response

[rew]

I have seen several posts over the last few months about the quality of the AM sound and how much better some of the older radios sounded than what is out there today. I have several old car radios laying around somewhere, one was an AM only from a 64 chevy. and also some of the older tube receivers and some newer ones from on up into the 70's. I was planning on connecting them to a communications service monitor and running a frequency response graph on each of them and compair them to some of the units out there today. Sort of a proof of performance test like used to be required on the control board through the transmitter.
I was wondering if anyone has tried this.
My plans to run this test have been put on hold due to a heart attack and surgery. It would kill me to pick up the service monitor now. I am laid up for at least a month so I am coming up with these ideas and nobody to talk about them with. Wife and daugther don't speek radio.
If anybody has done this test please post the results. I will get around to doing this one day. It would be interesting to have something to compair it to.

 

[Studio1]

Haven't done any performance testing on today's receivers, but with the decline in AM services most cheaper radios have only mediocre performance on the AM band.
Without a doubt, older receivers have superior performance on all bands as they were engineered to a specification, not to a price.
My 1980s Technics receiver will pee all over this modern 'junk' which originates from china.
It even has front-panel switchable IF band-pass filtering, which really helps to cut down noise on distant or low powered FM stations.
I don't doubt there are performance sheets out there for various types and brands of receivers, but these days hardly anyone is worried about how their unit measures up, especially the iPod generation who invariably don't listen to radio anyway.
There is always interest in how a particular amplifier stacks up against the competition, but less interest in receivers etc.

As a broadcast engineer, I've done a bit of work with AM in the past. Not so much these days as the number of AM services in this country has dropped and they're all looked after by other companies. The bandwidth being fed to the transmitters is usually pretty good - anywhere from 10 - 15 kHz wide, but people's receivers generally don't have the same response, and people complain that AM sounds bad as a result.

 

[RadioMan203]

I remember back when I was engineering an AM daytime that had gone Kahn stereo that the response over the in-house Belar modulation monitor was outstanding. There were a few handful of radios that made AM shiny but with receiver manufacturers already placing more engineering into the FM side of things it wasn't surprising to see a decline in performance.

Also, remember when the NRSC-1 curve came to be in the late 1980's - that didn't help AM in the least with a 10 KHz cutoff. I heard that some stations actually limited their bandwidth down to 5 KHz. This type of action would provide little incentive for improvement in AM circuitry.

I have a couple of old tube AM receivers and their audio response if far superior to the vast amounts of junk passed off today.

 

[317C50KW]

If you are a member and have access to the National Radio Club's "DX Audio Service" check out the monthly "bandscan" segment produced by one of their contributors (Mark Durenberger). He's using a Perseus SDR. Many of the well engineered facilities sound downright amazing on his recordings, even the signals that could use some attention sound acceptable.

I know the Perseus SDR is now a non-supported product by its developer but that is one interesting piece of software for radio geeks. It's still available for sale.

 

[1L6E6VHF]

One thing to remember with AM receivers is that while some older AM receivers had great frequency response, others had narrow frequency response, and it was not an issue of quality, rather that the preference of the design engineers.

For the most part, frequency response in an AM receiver is inversely proportional to the selectivity of the receiver. This is because of the nature of the sidebands on an AM signal. If your AM station on 1400 is playing a song that has (for example) the "tingle" of a triangle being struck, with a harmonic note at 14 kHz, the sound of that harmonic is actually being transmitted on 1386 kHz and 1414 kHz- beyond the centers of the adjacent channels! If you are to hear that "brilliance", the IF chain will have to be so wide as to allow the adjacent channels through the bandpass. This will increase the noise on the signal due to interference (in worst case, you'll actually hear a station on 1390 or 1410 instead} of the one you wish to listen to on 1400).

To get rid of the interference, you narrow the receiver, to the point where all the "brilliance" is filtered out (you have a "communications receiver").

Some radios, like the Sony SRF-A-100 AM stereo radio of the mid-1980s, had a bandwidth switch to deal with the problem.

As time progressed, AM receiver sections generally got narrower, to cut back on noise (since by about 1980 or so people were beginning to consider AM a spoken word medium anyway), or even to make the receiver sound "better" on FM (by making the AM sound duller in comparison).

In recent years, many radios, especially car radios, are very selective, then have 5 kHz cutoff filters ion the audio stage, to filter out the waterfall noise caused by the IBOC signals starting about 5 kHz from the carrier.

Furthermore, some radios are just plain lousy on AM - having a narrow center bandpass, but poor rejection outside the bandpass, which can cause poor selectivity AND low fidelity.

 

[Kmagrill]

Considering that most modern AM tuners use ceramic IF filters instead of tuned circuits, why are both selectivity and bandpass poor on some receivers? I thought ceramic filters could have excellent bandpass and still have tight skirts just beyond the pass.

 

[satech]

Basically there are two tiers of AM radio tuners in mass production today:

More expensive radios, especially car radios, use DSP-based digital tuners which employ sharp "brickwall" audio cutoff filters, offering an audio response up to somewhere between 4 and 6 kHz and then sharply dropping off above that point. Many of these cut off the audio at 4.5 kHz because they are "world market" tuners designed for Europe, where MW stations have 9 kHz channel spacing and are tightly packed on adjacent channels. But I have also seen some modern DSP-based car radios whose audio on AM is flat up to 6 kHz and even employs varying treble response depending on the signal strength (so strong signals sound bright and crisp while weak signals are more narrowband to reduce background noise).

And then you have the cheap low-cost, low-quality tuners found in things like boomboxes, Walkmans, and clock radios, which have cut down on the number of IF stages and filters to reduce production cost, and thus are often very wideband on AM, both in terms of selectivity and audio response. Needless to say they don't perform well, but if you have a strong local AM station, they can sound surprisingly "hi-fi" and will let you hear the full 10 kHz NRSC AM audio bandwidth, especially if it's an analog tuner which can be slightly off-tuned away from the center of the signal.

 

[JohnnyElectron]

"AMAX" marked tuners/radios are/were 'da-bomb' on the AM band.
The Sony SRF-A100 had a 2 position (bandwidth) switch, in wide and the treble turned-up, it was around 12KHz audio response (and stereo AM too). The Sony home tuners sold in Canada in the 80s with AM stereo also had a 2-position bandswitch - it exceeded 10KHz, but had a 10KHz 'whistle' filter that actually reduced the audio!

The GM Delco "UX-1" car radio with "AMST" button and 5 band EQ (circa 1987-1993) was exceptional, as were the Chrysler (Infinity) radios that had a 5 band EQ and "joystick" speaker fader (around 1994-1996) which also had stereo AM and super AM bandwidth.

Then there's the top of the line: Fanfare FTA-100, Denon NAB and Carver AM stereo tuners that had 15KHz audio response.

I believe to use the "AMAX" mark, non-portables had to have at least 7.5KHz frequency response and portables 6KHz response.

 

[Kmagrill]

The GM Delco "UX-1" car radio with "AMST" button and 5 band EQ (circa 1987-1993) was exceptional, as were the Chrysler (Infinity) radios that had a 5 band EQ and "joystick" speaker fader (around 1994-1996) which also had stereo AM and super AM bandwidth.

Exceptional is a relative, and perhaps a bit too generous, term. The Delco radio actually debuted in the high end '85 cars. Compared to most of the other automobile AM radios, I suppose they were better. I did extensive response tests on the Delcos in the wideband mode. They were kind of flat (within 4dB) to 6kHz with a steep rolloff to -20dB at 12kHz. Audio could still be measured out to 16kHz, but just barely. Noise immunity was poor in wide mode. Could have used a noise blanker in wide mode. Made driving under bridges and power lines painful to endure. They never sounded anything like FM. It also happens that 5kHz is an audio frequency known to be especially irksome to female listeners. With a top frequency just above 5kHz, the audio band masking made those particular frequencies really stand out. Most unfortunate.

 

[AMradiofan]

The Carvers do, indeed sound GREAT, and I wish they, or something similar was available for the average "audio joe" today other than on the secondary market. It would help with AM-band marketing. (though people continually argue AM is dead, our experience is that it IS of great interest.) We just started piping a carver directly UPstream to our streaming provider. We didn't go directly from the board, the processor, or the mod monitor because we wanted to send OUT to the world what AM stereo can actually BE!

The results are spectacular, and the response equally impressive. In one week, we've had listeners all over the United States, and some in other countries. Some have commented on the sound, and NONE have been "turned off" by the fact it's AM. Listen to a real Carver online
at our website, www.i1430.com or find WION in your google play or I-tunes store for the lesser quality stream. (still better than many mp3 streams!!)

Now, how can we, as an industry politely push/ask a good manufacturer to produce an AM stereo receiver again? Even in the 1980's, some tuners at JC Penny came with stereo, so it IS possible to sell it, even in lesser-known retail circles for audio!

 

[ChiefOperator]

Now, how can we, as an industry politely push/ask a good manufacturer to produce an AM stereo receiver again? Even in the 1980's, some tuners at JC Penny came with stereo, so it IS possible to sell it, even in lesser-known retail circles for audio!

That's the million dollar question. Yes, AM does (can) sound good. One of my AM's monitors off the mod monitor, and the audio is incredible.

 

[Kmagrill]

The Carvers do, indeed sound GREAT, and I wish they, or something similar was available for the average "audio joe" today other than on the secondary market. It would help with AM-band marketing. (though people continually argue AM is dead, our experience is that it IS of great interest.)
....
Now, how can we, as an industry politely push/ask a good manufacturer to produce an AM stereo receiver again? Even in the 1980's, some tuners at JC Penny came with stereo, so it IS possible to sell it, even in lesser-known retail circles for audio!

I'd be curious to know what the real world demodulated audio performance actually is from one of those. Most of the AM stereo radios had frequency responses to less that 7kHz. Certainly not FM-ish quality for the ones that I've personally listened to.

As for making new AM stereo radios, there are some DSP based systems for HD that also decode C-Quam, but I believe that the Motorola line of AM stereo decoder chips are out of production, now. If that's right, then it would take a big production commitment to have more made.

 

[GeneSavage]

Wow... listening to WION's feed right now and it is GORGEOUS.

As far as frequency response, it looks like they're holding to the NRSC standard: frequency response starts to roll off somewhere between 9,5000 Hz - 9,7000 Hz. Between 9.7 Khz and 11 Khz it drops off sharply, and then is noise floor from that point up to 22 Khz (likely the noise floor of the sound card).

The station's processing is impressive: it looks dense on a 'scope, but sounds very open and non-crushed on the radio. I'd be happy if a local FM sounded like this, much less an AM.

If I had any complaint, it would be on Mike + The Mechanics "Living Years." The audio was off-balance, the right channel was low, and it sounded like there might be some noise reduction kicking in, making a minor problem a little worse. I doubt most listeners would care, but since you encourage critical listening, it seems out-of-place.

Overall, very very impressive. If AM stations had music programming like this in the 80s, and AM stereo receivers had sounded like this, maybe the band could have stayed competitive. Hats off for an outstanding broadcasting plant!

...Oh, an if that TX11a ever disappears, check and see if there's a guy in the Tulsa area newly grinning ear-to-ear... what a receiver! I've always wanted one of those...

 

[bmcglynn]

The GM Delco "UX-1" car radio with "AMST" button and 5 band EQ (circa 1987-1993) was exceptional, as were the Chrysler (Infinity) radios that had a 5 band EQ and "joystick" speaker fader (around 1994-1996) which also had stereo AM and super AM bandwidth.

Compare that to a modern GM radio, and it is another story. I often travel to visit clients and that requires renting cars in different cities. I have to say that the absolute worst sounding radio I have ever heard in my life came out of a new Chevy Fuze. The AM section sounded no better than a telephone conference call. There was no low-end to speak of below 500 Hz and no high end above 3Khz. I got a headache listening to the radio and had to turn it off.

This makes me believe was this an oversight because the design engineer tried to mimmic the frequency response of a telephone? What it did was make me think of the car as cheap and tinny just by pure perception. In the marketing world, perception is reality.

What bothers me, despite having a financial interest in the AM band, is that poor electronic design is detrimental to the auto industry and the radio industry.

Think about it from a pure marketing perspective. Stations in the leading metro areas targeting some of the most attractive demographics are on often AM (in New York - WCBS, WINS, WBBR). If you're renting a car, turn on the radio to listen to traffic or news, and hear tin audio - your perception of the car is that it could be tinny, not solid, or just plain cheap.

Sure, the radio had all sorts of things I don't care about for a commute. I want traffic, weather, and news - and I want it with the simplicity of dialling up 880 KHz instead of futzing with Apps, Bluetooth connections, and other annoyances before I've had my morning coffee.

Besides doing a disservice to the broadcaster's clients by presenting their ads through what sounds to be a pair of tin cans with a string tied together, it also could have an impact on car sales.

The first question that would be asked is - who would make an auto purchase decision based on the quality of a radio? The less obvious question is what is the financial impact from lost car sales because the prospect thought the car felt "tinny"? Those things matter. I know of companies that put metal weights in remote controls to make them feel more "solid".

My perception as a new car buyer - I feel that Ford has a more solid product. Why? When I listen to All-News radio, it sounds full, rich, boomy, solid. The Fords I sometimes rent have HD radio. Like HD or not, AM HD addresses the AM noise issue and sounds a lot better than "Conference-Call" radio.

Compare today's to a 1992 Cadillac radio's AM Stereo sound with full 10KHz bandwidth and Stereo.

Brian

 

[meduci]

The Carvers do, indeed sound GREAT, and I wish they, or something similar was available for the average "audio joe" today other than on the secondary market. It would help with AM-band marketing. (though people continually argue AM is dead, our experience is that it IS of great interest.) We just started piping a carver directly UPstream to our streaming provider. We didn't go directly from the board, the processor, or the mod monitor because we wanted to send OUT to the world what AM stereo can actually BE!

The results are spectacular, and the response equally impressive. In one week, we've had listeners all over the United States, and some in other countries. Some have commented on the sound, and NONE have been "turned off" by the fact it's AM. Listen to a real Carver online
at our website, www.i1430.com or find WION in your google play or I-tunes store for the lesser quality stream. (still better than many mp3 streams!!)

Now, how can we, as an industry politely push/ask a good manufacturer to produce an AM stereo receiver again? Even in the 1980's, some tuners at JC Penny came with stereo, so it IS possible to sell it, even in lesser-known retail circles for audio!

meduci sells the new PRO1k+ component quality tuner. This is a niche product intended to fill a void in the market.

 

[kenglish]

I'm still trying to find out who owns the design for the McKay-Dymek stuff. I found a cache of parts from the former Stoner Communications recently. Mostly just generic stuff though.
I wonder where the tooling, designs of the boards, etc went.

 

[PTBoardOp94]

The first question that would be asked is - who would make an auto purchase decision based on the quality of a radio? The less obvious question is what is the financial impact from lost car sales because the prospect thought the car felt "tinny"? Those things matter.

Take off your engineering hat and ask yourself how far down the radio is on someone's list of features on an automobile. I've bought two (used) cars in the last five years, and I didn't check the AM radio for quality before buying either time. Not because I don't use the AM section at all, because I do sometimes. But I value the engine, and the steering, and a dozen other things before the frequency response of the radio.

 

[bmcglynn]

Take off your engineering hat and ask yourself how far down the radio is on someone's list of features on an automobile. I've bought two (used) cars in the last five years, and I didn't check the AM radio for quality before buying either time. Not because I don't use the AM section at all, because I do sometimes. But I value the engine, and the steering, and a dozen other things before the frequency response of the radio.

In marketing terms the same argument applies. The point I hi-lighted is around perception and what the lost opportunity in sales would be due to perception - not an explicit choice based on the quality of an AM radio.

Is every person going to check the AM radio before buying a car? No - in fact I doubt anyone will when shopping. However, out of 12 million+ new cars sold in the US in a year, how many people (some of whom are less concerned about engine performance) will form an opinion on general perception of a car they rented or took a ride in?

What is the incremental cost to put in decent frequency response? Probably zero - maybe even less than zero in that extra effort and parts are necessary to shape audio to match a telephone. With a DSP - it is only a design parameter. What is the opportunity cost of a lost sale due to perception projected by blatantly poor audio?

Heck, maybe even out of 12 million potential buyers, there is that one person that decides to buy a car for an AM radio...

BTW - The nice people at Avis decided to give me a 2013 Toyota this week. The AM section sounds very good.

Brian

 

[BobOnTheJob]

The GM Delco "UX-1" car radio with "AMST" button and 5 band EQ (circa 1987-1993) was exceptional, as were the Chrysler (Infinity) radios that had a 5 band EQ and "joystick" speaker fader (around 1994-1996) which also had stereo AM and super AM bandwidth.

I have to say that the absolute worst sounding radio I have ever heard in my life came out of a new Chevy Fuze. The AM section sounded no better than a telephone conference call. There was no low-end to speak of below 500 Hz and no high end above 3Khz. I got a headache listening to the radio and had to turn it off.

My wife just got a 2012 Toyota RAV4 and based on other Toyota radios I'd heard, I expected the AM to at least be tolerable. Take everything described in the above and add a healthy dose of "hollow" to it and you've got this radio. First station I checked was one that a friend built & I was wondering what went wrong with the build. Later on that trip, I tried it on WLAC 1510 Nashville (a station known to have listenable quality) and it was WORSE than the first station I heard. I did without the news and traffic update. Absolutely no one would be willing to attempt to listen to that radio's AM audio...in a word, it's essentially unintelligible.

 

[hvz]

Heck, maybe even out of 12 million potential buyers, there is that one person that decides to buy a car for an AM radio...

For AM you might be right - although I live in the Netherlands and AM is really as good as dead here (at the last frequency auction here a few years ago, some stations paid upto 80 million euro for 8 years of nationwide FM coverage - but one guy bid on several AM frequencies that can be received even far outside the Netherlands and he got them for 5000 euro.)

But, since it's getting more and more difficult to put a different radio in a car since it's usually tightly linked to the car and also contains a navigation system etc, I would say it's getting more important. When I bought my latest car (a Toyota Auris hybrid), I made a test drive in one and the quality of the radio (probably caused by the speakers) was so bad that I decided to put in new speakers as soon as I received it. Fortunately, when I got the car it turned out that the audio system was much better than that in the car in which I made the test drive, so I didn't have to - in fact it's so good that at some stations that I visited I've taken people to my car to compare the audio because the car radio sounded better than what they had in their studio.