Radio from circa 1990 which claimed to make AM sound as good as FM?

[BMR]

I'm rapidly approaching the age where the memory starts to play tricks, but I'm sure I can remember hearing about a much hyped radio from something like 1990, 91 or 92 which claimed to make AM sound as good as FM, but cost into the hundreds of dollars.

I think I remember hearing it reported on several radio news programmes - 'Sweden calling DXers' and Radio Netherlands 'Media Network' spring to mind as having mentioned it.


Does anyone remember this? Did anyone own such a radio?

Have I made the whole thing up?

 

[rbrucecarter5]

I'm rapidly approaching the age where the memory starts to play tricks, but I'm sure I can remember hearing about a much hyped radio from something like 1990, 91 or 92 which claimed to make AM sound as good as FM, but cost into the hundreds of dollars.

I think I remember hearing it reported on several radio news programmes - 'Sweden calling DXers' and Radio Netherlands 'Media Network' spring to mind as having mentioned it.


Does anyone remember this? Did anyone own such a radio?

Have I made the whole thing up?

McKay Dymek made very good AM Tuners - but much earlier, in the 70's. They had a stand alone tuner and a matching antenna unit.

!990 was on the trailing edge of AM stereo - any AM stereo radio (still) sounds great even if receiving a mono station, because they use product detectors instead of envelope detectors.

 

[davideduardo]

McKay Dymek made very good AM Tuners - but much earlier, in the 70's. They had a stand alone tuner and a matching antenna unit.

I had one of the Dymek receivers... about $1350 in 1978 dollars. It had a selectivity control with essentially controlled fidelity. The maximum setting was 10 kHz, but it had the most gradual or "unsharp" of the filters. It definitely did not make AM sound as good as FM, even in those pre-NRSC mask days as few AM transmitters were flat above 10 kHz.

Here are the audio specs for a Harris MW-10 (one of which I installed) in the mid to late 70's time period. Note that it does not even rate the performance over 10 kHz.

AUDIO FREQUENCY RESPONSE: -/+1 db. 20 to 10,000 Hz. (Response referred to 1 kHz, 95% modulation, with modulations at other frequencies held to
same percentage. Response may degrade at higher modulating frequencies
if transmitter is operated into a bandwidth limited antenna
system.)

 

[rfry]

AM vs FM

In the mid-1960s I was a staff engineer at WJR/WJR-FM in Detroit. When not on duty I usually monitored those transmit systems in my low-rise apartment using a McIntosh MR-55A AM/FM tuner (with minimal receive antennas), along with a high-quality audio amp driving an AR-2a speaker.

My apartment was located about 15.6 miles from the transmit site of WJR, and across the street from WJR-FM on the Fisher Bldg in Detroit. Those stations simulcasted in those days.

The difference in the S/N, audio bandwidth, and distortion that I heard as transmitted by WJR and WJR-FM was difficult to detect, by listening.

Also note that these days, very few consumer-level AM broadcast receivers accurately can receive/reproduce transmitted audio frequencies much above 4 kHz or so -- even if they exist in those transmissions.

 

[rbrucecarter5]

In the mid-1960s I was a staff engineer at WJR/WJR-FM in Detroit. When not on duty I usually monitored those transmit systems in my low-rise apartment using a McIntosh MR-55A AM/FM tuner (with minimal receive antennas), along with a high-quality audio amp driving an AR-2a speaker.

My apartment was located about 15.6 miles from the transmit site of WJR, and across the street from WJR-FM on the Fisher Bldg in Detroit. Those stations simulcasted in those days.

The difference in the S/N, audio bandwidth, and distortion that I heard as transmitted by WJR and WJR-FM was difficult to detect, by listening.

Also note that these days, very few consumer-level AM broadcast receivers accurately can receive/reproduce transmitted audio frequencies much above 4 kHz or so -- even if they exist in those transmissions.

WRONG again! ALL - as in ALL AM home receivers made in the last couple of decades are inherently broadband. Three reasons:

(1) An effort to reduce cost by reducing the IF components to the bare minimum.
(2) Cheap tuning mechanisms in radios are so sloppy it is hard to get on a station, so a wideband IF makes it easier to tune with a pitiful tuning mechanism.
(3) Inaccurate tuning voltage steps in digitally tuned models. If the IF was only 4 kHz wide, you would not be able to tune to the stations over part of the band.

The old All American five tube circuit with two IF stages, and all Japanese 6 transistor circuits with three IF stages have not been produced in decades, I had a hard time even finding one to analyze:

http://earmark.net/gesr/Current_Radio_Design.htm

The ONLY reason why an AM radio today would have limited frequency response is that they put an RC low pass filter on the audio.

 

[rfry]

... ALL AM home receivers made in the last couple of decades are inherently broadband. ...

Not as far as the audio response heard from those receivers by their listeners.

OTOH the audio response of an AM broadcast transmitter can extend from 20 Hz to 9.5 kHz or so, using the NRSC recommendation.

 

[gar hi]

I thought AM stereo was so fascinating in the mid 80's.

I had gotten my Sony AM Stereo Walkman a little while before I moved down to Florida and I couldn't get enough of hearing WNBC in stereo and the local WFIL when they had a short run as an oldies station.

At night, WLS came in great in stereo and I remember they had a different system for stereo than did WFIL and WNBC. There were two settings on the radio for the two methods being used.

When I was in Florida, it was interesting hearing WNBC in stereo at that distance and WLS which was a lot stronger. DXing at night took on a whole new meaning, as there were many AM stations to be heard in stereo.

The local 1380 in Tampa/St. Pete was stereo and a simulcast of WRBQ 104.7 FM

I actually thought AM Stereo sounded better than FM because I was able to compare hearing the same thing switching between both stations on AM and FM.

AM stereo had a more 'solid' sound to it and after listening to it for a while, FM sounded too high pitched.

I guess AM stereo was an attempt to save top 40 on the AM band and it's a shame it wasn't successful.

 

[rbrucecarter5]

The stereo separation was certainly better on AM stereo, as was the frequency response on the low end. When you live in wide open spaces, reliable FM in the car is about 130 miles, sometimes more for some stations under good conditions. But AM stereo hangs in daytime for about 300 miles, for regional low band stations. Meaning that on isolated stretches of road, which make up a whole lot of the western 2/3 of the nation, AM stereo is a better system in cars than FM stereo.

 

[Schroedingers Cat]

The closest I ever heard to FM sound on an AM station was when CKLW was in AM Stereo. CKLW didn't have the 15 kHz cutoff restriction that US stations had. I listened on a Sony SRF-A100 with Sony headphones and also plugged it into amplifiers. It had a 32 Ohm output as I recall, which didn't give a perfect match on many amplifiers. Seems like CKLW used the Harris system, and changed the exciter to the Motorola Pilot, etc. when it became the de facto standard. I listened to CKLW and other stations also with the Sony SRF-A100. When in the wide bandwidth position, the thing seemed like FM in locking in on a Stereo signal like in the days of AFC. Another AM signal that sounded great in Motorola AM Stereo within a few miles of the transmitter was WSAM Saginaw. Leonard Kahn wanted me to call CKLW and try to talk them into changing to the Kahn system. But CKLW sounded really good with Harris with the Motorola modification.

 

[semoochie]

I thought AM stereo was so fascinating in the mid 80's.

I had gotten my Sony AM Stereo Walkman a little while before I moved down to Florida and I couldn't get enough of hearing WNBC in stereo and the local WFIL when they had a short run as an oldies station.

At night, WLS came in great in stereo and I remember they had a different system for stereo than did WFIL and WNBC. There were two settings on the radio for the two methods being used.

When I was in Florida, it was interesting hearing WNBC in stereo at that distance and WLS which was a lot stronger. DXing at night took on a whole new meaning, as there were many AM stations to be heard in stereo.

The local 1380 in Tampa/St. Pete was stereo and a simulcast of WRBQ 104.7 FM

I actually thought AM Stereo sounded better than FM because I was able to compare hearing the same thing switching between both stations on AM and FM.

AM stereo had a more 'solid' sound to it and after listening to it for a while, FM sounded too high pitched.

I guess AM stereo was an attempt to save top 40 on the AM band and it's a shame it wasn't successful.

There were two settings on the radio, alright, one for Kahn and one for the other four.

 

[gar hi]

Before I got my AM stereo Walkman, I did a thing with two portable radios I had along with my big stereo system.

I ran the auxiliary cable of the left side to one radio and the auxiliary cable for the right side to the other radio.

I plugged my headphones into my stereo system listening on the auxiliary setting.

On a station broadcasting in AM stereo, I tuned one radio to the left side of the frequency on the dial and the other radio to the right side of the frequency.

After a little fine tuning of both radios, the stereo sound was amazing!

 

[radioman148]

Before I got my AM stereo Walkman, I did a thing with two portable radios I had along with my big stereo system.

I ran the auxiliary cable of the left side to one radio and the auxiliary cable for the right side to the other radio.

I plugged my headphones into my stereo system listening on the auxiliary setting.

On a station broadcasting in AM stereo, I tuned one radio to the left side of the frequency on the dial and the other radio to the right side of the frequency.

After a little fine tuning of both radios, the stereo sound was amazing!

When WLS started broadcasting in stereo in the early 80s they recommended doing that.

 

[semoochie]

Before I got my AM stereo Walkman, I did a thing with two portable radios I had along with my big stereo system.

I ran the auxiliary cable of the left side to one radio and the auxiliary cable for the right side to the other radio.

I plugged my headphones into my stereo system listening on the auxiliary setting.

On a station broadcasting in AM stereo, I tuned one radio to the left side of the frequency on the dial and the other radio to the right side of the frequency.

After a little fine tuning of both radios, the stereo sound was amazing!

That's the Kahn system. When XETRA was performing tests(for about three years), I just used two radios, with one tuned slightly above and the other, slightly below 690. I described the sound at the time as like FM stereo with the door shut.

 

[gar hi]

I also remember the thrill of hearing KFRC San Francisco in AM stereo for the first time on one of my visits to see my brother out there.

And then at night, KFI came in strong in stereo too.

 

[rfry]

Followup: Audio BW of Modern AM Bdcst Receivers

The test report at http://www.nrscstandards.org/Reports/NRSC-R100.pdf includes many pages showing the measured audio response of many AM broadcast receivers including the C Crane unit below, as an example.

It is clear from all of those measurements that such receivers are not "broadband" compared to the performance of virtually any analog FM broadcast receiver.

 

[rbrucecarter5]

You are getting "broadband" confused with "audio response". They are two entirely different things.

Broadband refers to the IF response. If you don't believe me - just look inside any home radio manufactured within the past 30 years. One cheap ceramic filter. It may be a good model +/- 6 kHz, or it may be a cheap model, I have seen (and still have the filter) +/- 40 kHz. As a bonus to the receiver manufacturer, such a wide filter has a lot of loss, and makes the radio less prone to overload, which is a problem when the ultimate stop band rejection of the filter is only 40 to 50 dB.

Audio response is what you are reporting in the plots. All it takes is a single resistor and single capacitor to roll off the audio. That rolled off audio can contain audio from two or three stations mixed together if you find one of those awful +/- 40 kHz ceramic filters in the radio. But - you can tune the radio with that 3/8 inch tuning wheel that has exactly three numbers on it - 5.5, 10, and 17. In tiny font. I love radios like that, actually! They are ripe for hacking - take out the RC low pass filter and music sounds GREAT on them! I have at least 100 of those super sharp three element Murata 455kHz filters, that and a 200 mm ferrite bar antenna and you have almost GE Superadio performance out of a piece of junk that cost $5 at the Dollar store.

Of course narrowband IF will also limit the audio response, but you aren't going to find that outside of car radios and expensive models like CCrane -which, by the way, uses that super sharp Murata filter and adds a single tuned RF stage in front of the SAME radio on a chip used in Dollar store radios.

I made the mistake of confusing narrowband and audio response when I was about 20. I had the bright idea of trying to increase selectivity of my radio by narrowing audio response. It didn't work. All I got was rolled off hash from the adjacent station. Learning from my mistake, I synthesized a proper IF by designing a 4 ceramic filter IF section for my radio (based on a Heathkit GR-78 circuit). Now THAT gave me the selectivity I was after, and an "A" in a EE class at college.

Yes - I do design and build radios from scratch, so I know the difference between IF response and audio response. Perhaps the people running these tests should learn the difference, so we don't all end up with HD sidebands in our radio's audio, just attenuated in a single pole RC low pass filter, which doesn't do an adequate job of filtering the hash out.

 

[rfry]

A few observations:

... Audio response is what you are reporting in the plots. All it takes is a single resistor and single capacitor to roll off the audio.

That de-emphasis circuit would not produce the loss of lower audio frequencies shown for most receivers in the NRSC study.

... I know the difference between IF response and audio response. Perhaps the people running these tests should learn the difference, so we don't all end up with HD sidebands in our radio's audio, just attenuated in a single pole RC low pass filter, which doesn't do an adequate job of filtering the hash out.

Filtering out such hash received from adjacent-channel AM stations running HD is impossible without also adding distortion to the demodulation of a desired analog-only AM station, because their r-f spectra overlap (see graphic below).

 

[Schroedingers Cat]

High C on the piano is about 4.2 kHz, which is about 20 dB down in the graph Rich posted. You would miss all the High Cs in "Nobody But Me" by the Human Beinz, probably even the 6:00 alarm in "Daydream Believer" by the Monkees, and just about any cymbals.

 

[frankberry]

As far back as the late 70's some Marantz (and other) receivers and tuners included an AM ceramic filter in the IF section. It was included to improve selectivity, which it did. It also ruined the AM high frequency response.
In one case, the Program Director of an AM station where I was the Chief Engineer complained bitterly about the sound of his new receiver when listening to AM.
I opened up the receiver, found the ceramic filter and removed it ... bypassing it with a capacitor.
The AM sound quality was vastly improved.

Just as the bandwidth of the radio station's RF system (from the output network in the transmitter to the Antenna Tuning Units) have an impact on the station's high frequency response, the bandwidth of the IF section of the receiver will have an impact on the receiver's high frequency response.

 

[Schroedingers Cat]

The Technics ST-G5 Series Tuners had an automatic bandwidth selector on FM, which could be overridden and selected manually. I've always thought that high end tuners and receivers should have switchable bandwidth at the very least, so that you can have better frequency response or better selectivity depending on conditions and the type of programming you are listening to.