This page is under construction. Our contributor David Smith (not to be confused with David "Anonymous" or David Rich) kicks things off with this essay.
AM radio has a long, rich history, with the first commercial U.S. broadcasts beginning in the early 1920s. By the 1930s, the early phase of technology was maturing with superheterodyne radios and receivers being the norm and some great sets being made by communications specialists like Hammarland and Hallicrafters and by radio set makers such as E.H. Scott and Zenith. AM radio served the nation well, but a desire for greater fidelity and immunity from atmospheric interference got experimenters (specifically Edwin Armstrong) working on the FM process. Still, FM wouldn't become a factor until well after WWII and AM sets continued to evolve. The hi-fi boom of the '50s became synonymous with the new LP and FM broadcasting, both being pushed by the new component hi-fi set makers. When FM became popular, for the most part, focus shifted to FM tuner design, and AM sections became a low-cost add-on feature of barely acceptable performance. There were, and still are, exceptions, and these are what will interest us most. But first a bit of background.
AM stands for amplitude modulation. A carrier frequency (the nominal frequency that you tune to such as "1210 on your AM dial") has its amplitude modulated with the intended audio signal. You can actually see the waveform of the audio impressed on top of the carrier. Benefits are that AM was a very easy modulation scheme to use in the early radio days and, more importantly, very easy to receive and demodulate.
This is an important point to make regarding AM: it's actually pretty easy to make a functioning AM tuner. The frequencies are relatively low. RF amplification is plentiful, demodulation can be extremely simple. The AM broadcast band is at the noisy end of the RF spectrum, so phenomenal sensitivity isn't required. A superheterodyne tuner can be achieved with three transistors and a diode, or a single IC. In the tube days, millions of AC/DC radios were sold with four-tube plus rectifier layouts. Usually the performance bar for AM was set pretty low. There are a lot of high-end FM tuners that have the bare bones of an AM section added just so that you can pick up a little talk radio. In fact, why would you want anything more?
The main reason is for the fun of AM. Programming on AM is different from FM with an emphasis on talk radio for sports, news, politics and personal advice. In fact, AM is "funkier" with all manner of oddball programming that wouldn't be mainstream enough for FM. For me, AM also reminds me of my youth, with late nights spent trying to drag in distant stations on a homemade set, or the drive from Cincinnati back to Cleveland late on Sunday night after visiting my wife-to-be at grad school. The old Chevy only had AM, but listening to WLS in Chicago and other stations would keep me awake. Others will find AM essential to pick up a station or information that they can't get on a local FM station. I listen regularly to NPR, unavailable in Canada, from WNED-AM, a Buffalo, New York station. Even though most of these examples are talk-oriented, a better-sounding AM tuner makes the listening more pleasurable. And there are still some worthwhile music stations on AM.
The most useful AM tuner feature. With AM, daytime and nighttime reception are very different cases. Daytime reception is good for local stations, with a range similar or a little further than FM's range. The range is not so great as to cause a lot of interference from stations in distant cities. Nighttime reception becomes very long distance. On any night, I have no problem picking up stations from all over the east coast from my Toronto location, including New York City, Atlanta, Philadelphia, Boston, Cleveland and Chicago. So we have daytime reception which is good for local stations and nighttime reception where huge distances can be covered and the band becomes chockablock with stations. We have a system that isn't immune to interference as FM is (no AM rejection or static rejection, no capture effect). We want wide bandwidth for best fidelity but require narrow bandwidth for rejection of adjacent channels and atmospheric noise. It isn't hard to see why the most useful feature on a "better" AM tuner would be to have multiple IF bandwidths. With dual bandwidths you can have a narrow setting for cutting through interference and a wide bandwidth for maximum fidelity when a station is in the clear. Readers of this site are well aware of the desirability of dual bandwidths in better FM tuners. They probably don't realize that the idea originated in AM, where its effect is much more obvious and essential.
IF bandwidth becomes the central parameter defining the sound of an AM tuner. In fact, assuming no significant audio response shaping after the detector, the IF bandwidth, the IF filter's corner shape and falloff slopes are all directly translated into the audio frequency response of the tuner. Generally, due to the double-sideband nature of the signal, the IF bandwidth divided by two equals the audio bandwidth. Thought of another way, the carrier frequency, tuned to the center of the IF, becomes the new DC frequency, and all sidebands will have audio pitches directly related to their distances from the carrier.
This applies to adjacent stations as well. Say you are tuned to a station at 900 kHz and another station of similar strength is on the next available slot above, 910 kHz. With AM reception, there is no inherent rejection of this adjacent undesired station. The highest harmonics of the 910 kHz programming will be closest and, rather than having their pitch defined by their distance from the 910 kHz carrier, they are now defined by their distance from the desired station carrier of 900 kHz. In effect, the audio frequencies for the adjacent station are inverted, with highest frequencies demodulating as lowest and lowest frequencies demodulating as highest. In fact, the 910 kHz carrier will be resolved as a 10 kHz fixed tone. The audible effect will be that the highest frequencies of the adjacent station will intrude as "splatter" if your IF bandwidth is narrow or indecipherable "monkey chatter" when the bandwidth is wide. The adjacent carrier will be a fixed whistle. Communications receivers tend to have very tight filtering with steep skirts to reduce breakthrough from adjacent or alternate channels, but clearly there is a tradeoff between this filter steepness and sound quality.
You can tune an analog tuner off the nominal center frequency a moderate amount and both improve the audio response and avoid possible interference on one side, although distortion will rise from imbalance between the two sidebands. One high-tech solution to this increase in distortion is a technique known as synchronous detection. Rather than using peak detection from a simple diode detector, an oscillator is locked in sync with the original carrier but at a high and constant level. This drives the detector harder and reduces the distortion due to full or partial fading of either the carrier or one of the sidebands. A more sophisticated version of this uses cancellation techniques to null out sidebands (and interference) on one side or the other. It is called "selectable sideband" and can really make a difference under the right conditions. For the most part, these advanced techniques have been available only on recent high performance shortwave receivers.
Whistle filters are also a desirable feature. As described above, another station may be located 10 kHz away (9 kHz in Europe) and its carrier would contribute a steady 10 kHz tone or "whistle." Better tuners such as the Scott tube tuners would include a deep and narrow audio notch filter at that frequency to remove the offending tone, hopefully without removing too much audio along with it. Later tuners used this feature less frequently. With steeper ceramic filters, the philosophy was just to roll the audio from 2 kHz and let the IF sharpness kill the 10 kHz whistle. It works, but at the cost of very muffled sound quality.
Some tuners used a combination of multiple IF bandwidths and several audio filtering steps to give more steps of total bandwidth. The McIntosh MR 55 and MR 66 use three IF filter bandwidths for "narrow, medium and wide 1," each with a whistle filter in place. The widest option, "wide 2," foregoes the whistle filter, extending the audio response of wide 1 from 8 kHz to 12 kHz. Fisher also had several tuners that used the same scheme. Another feature to look for would be 3-gang tuning and an added RF amplifier stage. While 4- and 5-gang tuning seems like the entry level to "better" FM tuners, you will rarely find more than 3-gang tuning in an AM tuner. Still, 3-gang tuning meant that a tuner had an RF amplifier ahead of the mixer stage and would have both better RF selectivity, to reduce image response, and a decidedly better weak signal noise performance.
The golden age of AM tuners. Stereo was first available to consumers around 1955, as two-track 7½" reel tapes. The stereo record was released in 1958. It wasn't until June of 1961 that the FCC final approved the Zenith approach to FM multiplex. In the meantime, the FCC allowed broadcasters to fill the void via AM/FM stereo simulcasts. Odd as it seems, the right channel was sent out on an FM channel and the left channel was sent out on AM. You may wonder about the matching of channels and the quality of imaging made in this way, but remember that this was in the very early days of stereo when it wasn't all that unusual to convert to stereo by picking up a second speaker that wasn't even of the same brand as your first speaker. ("Sound from the left and sound from the right - that's stereo!") I don't know how prevalent these broadcasts were, but evidently they were common enough that a number of tuner manufacturers built tuners to cater to them. They are easy to spot in that they are really two independent tuners on one chassis. Look for two tuning knobs, two dial pointers, and complex mode switching for FM, AM and AM/FM stereo.
The benefit here is not that any AM/FM simulcasts exist today but that, for these simulcasts, the manufacturers gave their best shot to making AM sections approach the sound quality of their FM sections. I won't say that they would fool you into believing that they were FM, but during daytime hours and using the widest bandwidths the AM sections did come passably close to FM quality. Typical specs and performance would be a frequency response of 20 to 8000 Hz (or wider with whistle filtering bypassed), with 0.5% distortion and a signal-to-noise ratio of about 45 to 50 dB. Most of these tuners come from the 1958-to-1961 era and include such notable sets as the Fisher 800C receiver, the McIntosh MR 66, the Scott 330 and 331, and several Heathkit and Sherwood models. Other sets from just before or just after this period had similar AM section properties, but without the fully independent tuner sections. For our purposes these would be equally desirable and would include the Mac MR 55, and the Fisher AM80 and FM90T variations. In fact, just about any AM/FM tuner from this era with 3-gang tuning and at least two positions of AM bandwidth is worth a try, and likely to give better AM performance than a lot of modern sets.
Post the vacuum tube tuner era, quality AM tuners became less common. Many of the flagship tuners would forego AM altogether, while the same companies left AM as an extra feature for their all-encompassing receivers. As ICs became more common in the late '60s, it became typical to have a single IC for the AM section. A double transformer/single ceramic resonator became the most usual IF selectivity device, and high selectivity seemed to win out over wide bandwidth as the overriding concern. By the "supertuner" era of the late '70s, the Leonard Feldman reviews in Audio magazine would praise any tuner that had response out to 5 kHz as being well above the norm!
Modern trends and AM Stereo
As AM demographics declined and broadcasters looked for something to give them an edge against FM, AM Stereo was offered up as something to bring back listeners. A number of systems were proposed by various radio equipment manufacturers such as Harris and Motorola. The FCC began testing systems in earnest in 1984. In their typical wisdom, though, they gathered all the data from laboratory and field tests, yet declined to pick a winner. Their attitude was to "let the market decide," and a number of systems went on the air. Radio manufacturers could choose to back a particular horse, to make multistandard receivers or, more typically, to stay out of the AM Stereo arena entirely. The FCC finally did decide in favor of Motorola and the C-Quam system in 1993, but by then consumer desire for AM Stereo had faded. A continuing shift of AM to talk and sports formats made stereo a moot point. A few hardy souls still broadcast in AM Stereo and might provide an interesting DX possibility. A list of AM stereo stations, and lots more interesting information on the subject, may be found here.
One benefit of the AM Stereo debacle was that frequency response standards were brought forward as an issue. The NRSC, an industry standards body, pushed for the adoption of standardized frequency response for transmitting and reception. It seems that although many receivers had audio response severely rolled off from 2 kHz, many broadcasters worked at keeping their transmitters flat to 10 kHz or higher. AM Stereo, as with FM Stereo, worked best with linear phase IF filtering which usually has a Gaussian or humped IF shape rather than a flat-topped shape. This would tend to roll off the AM audio at a gradual rate. Broadcasters were encouraged to use a pre-emphasis that mirrored this rolloff for a flat overall response. It was also felt that this pre-emphasis would roughly compensate for unsophisticated sets with narrow response.
Whether you have local broadcasters transmitting in AM Stereo or not, the few sets made by Sony, Carver and others might be worth tracking down for their better AM performance.
The latest technical shift for AM is the trend to IBOC (in band, on channel). This is a digital technique that adds multiple digital audio sidebands to the AM signal. The program content is carried both as a conventional AM signal and in duplicate as a 4½ second delayed digital audio signal. The thinking is that the consumer with an appropriate new IBOC-equipped radio will tune in to his favorite AM station and his radio will automatically switch over to a quiet and interference-free digital signal (when it is present). Some see this as the salvation of AM radio and others see it as totally ruinous. No one seems to be neutral in the matter except, perhaps, for the typical consumer who doesn't seem to care much at all. Two issues that should concern radio enthusiasts are that the digital sidebands seem to have little degrading effect on that channel' AM modulation, but can severely degrade the listenability of weaker adjacent channels. Secondly, any station that wants to convert to IBOC transmission must curtail its AM signal at 5 kHz, thus limiting its potential quality. The jury is still out about whether IBOC will flourish or go the way of AM Stereo. An optimistic view would be that, as with AM Stereo, a few receivers will be built with better-quality AM sections to showcase the technology. Time will tell.
As time permits, I'll add some capsule reviews of a few of my favorite AM tuners including my McIntosh MR 55 and MR 66, and Fisher R200B. Here is a listing of a number of sets that have a reputation for better AM performance. I'll leave it to other readers to give their impressions of these notable AM tuners and suggest their own favorites.
The Dynaco AF-6 has a reputation for a better AM section. They took a different approach for multiple bandwidths than others by having only one IF filter bandwidth which was used directly for the medium position. Wide and narrow positions were achieved by using audio EQ to boost and cut the high frequencies and expand or reduce the audio response.
The Heathkit AR1500 receiver also claimed to have a better-than-average AM section.
Some of the early Scott solid-state receivers include an automatically variable bandwidth "wideband" AM section. Armstrong in the UK had a similar feature.
The Sansui TU-X1 was legendary not only for its FM performance, but also because it used selectable sideband techniques for better AM audio and freedom from interference.
McKay Dymek had a number of better AM tuners like the AM3 with a companion amplified and aimable loopstick antenna.
Probably outside of the scope of this page would be a number of shortwave or communications receivers that had a great reputation for better AM. These range from as far back as the 1930s Hammarlund HQ120 up through the Grundig and Sony shortwave sets including the selectable sideband Sony models: the 2001D and current ICF-7600GR.
Our contributor and McIntosh expert Tim Britt chimes in: "The four tuners I think should be added are:
1. McIntosh MR 74: This has a great AM section and variable (wide/narrow) selectivity.
2. Accuphase T-100: This also has a great AM section, very sensitive and extended frequency response way beyond the normal 3,500 Hz cutoff used on must tuners.
3. McIntosh MR 75: This one has another super AM section in it, far
better than found in most tuners, though it does not have variable
4. McIntosh MX 117 tuner/preamp: Same AM tuner as in the MR 75.
5. McIntosh MX 113 tuner/preamp: Same AM tuner as in the MR 74, but I believe that the audio output of the MX 113 uses the MX 113's phono preamp (with significantly reduced gain) as the audio output amp for the tuner section. I would hypothesize that the sonic consequences of this are much less audible on AM than on FM.
And if receivers are going to be listed, the tuner in the MAC 4100 receiver is identical to the MR 75 tuner and has great AM.
The FMtuners group sometimes gets requests for an inexpensive but good AM tuner. IMHO, the best for the least amount of money is the GE Superadio III, available from many Internet sellers generally for under $50. The Superadio II was considered a much better radio but is no longer available except used on eBay. The SuperRadio III is an inexpensive way to add quality AM to an existing system as it has a headphone outlet jack that can be input into an AUX jack of someone's audio system to listen to AM through the system.
And while David has mentioned the McKay-Dymek AM tuners, McKay-Dymek also manufactured two powered tunable AM antennas that were quite small that significantly increased the performance of McKay-Dymek AM tuners, as well as any other good AM tuner they were attached to. The two models are the DA5 and the DA7. They are powered and tunable AND the short antenna section can be rotated almost 360 degrees for best reception. I used a DA7 coupled with the AM section of a Sony ICF-2010 shortwave unit to listen to WBT, an AM station in Charlotte, NC when we lived in Arlington, Texas to pick up their broadcasts of UNC basketball games after the sun went down. This combo worked amazingly well with almost no fading, and we used it until we put up a 10' C/Ku Band dish and found out we could get the live broadcasts from the venues. Then we retired the McKay-Dymek antenna and the Sony ICF-2010. McKay-Dymek also made a line of shortwave receivers but they were not great performers, were quite expensive, and got average-to-mediocre reviews in the shortwave magazines and publications.
I'm also aware that there were many mono FM tube tuners made with great
AM sections in them, but I know zip about them and would hope as the AM page grows, others who know more could contribute."
Our contributor Eli offers this nice writeup on indoor antennas for AM radio.
"I've compared the following:
1. Small loops (like those that come with most new tuners).
2. The Terk AM-1000 Advantage passive tunable loop (linked below)
3. The C. Crane Twin Coil Ferrite AM Antenna
4. The McKay-Dymek DA-9 shielded ferrite rod directional AM antenna.
5. The McKay-Dymek DA-100D All Wave Receiving Antenna.
The Terk is a great little antenna. I think it looks good and it's well put together. It's pretty easy to tune and makes a very big difference in reception compared to the stock, untuned loops. You can orient it to minimize noise, but you can only do this in one dimension (rotating around the vertical axis). It can greatly improve reception of local stations and allow you to receive some distant stations that would be impossible with the untuned loops. It connects to the antenna inputs on your tuner, but it can also improve reception on any radio that doesn't provide connections for an external antenna, as long as the radio has a built-in ferrite bar. Just move the loop close to the internal ferrite antenna, then tune it and orient it as you normally would. They are available all the time on eBay for $15-30. I was lucky enough to find one that someone was throwing away, but I would certainly pay up to $25 for one. You can read the owner's manual here.
The C. Crane Twin Coil is the next logical step up. It's amplified; it's
tunable; and you can orient the antenna in all dimensions and locate it wherever you want by means of its extension cable. You can buy longer extensions if you really want to mount it up to 75' away. I put mine up in the attic and used the 50' extension cable. It comes with a ferrite coupler, too, so you can use the antenna with radios that don't have antenna connections (as above with the Terk, but implemented much more elegantly with the C. Crane). The construction quality is very good and the control unit is small and unobtrusive. The controls are easy to use. The C. Crane is much more selective than the Terk. There are two tuning dials for coarse and fine tuning, and you really need the fine tuning to zero in on the desired frequency. Because you can orient the antenna unit in all directions to minimize noise and locate it far away from all the noise sources in your listening room (computers, light dimmers, refrigerators, flourescent lights, etc) and because you can get the antenna up much higher than your listening room, the signal to noise ratio I can achieve with the C. Crane antenna is better than with anything else I've tried. I paid about $70 for mine on eBay, then I bought the extension cable
from C. Crane directly.
This antenna is really impressive. You are way better off buying this
antenna with a $20 radio than spending $150 on a radio with a lousy antenna. The only (minor) problems I have with it are:
1. It's really easy to forget to turn it off when you are using battery power (it will run on AC or batteries). I've run down the batteries several times already by leaving it on by mistake.
2. The only feature I miss on this antenna is a variable signal attenuator, but you can buy a variable attenuator at Radio Shack for $5. I bought one but haven't actually tried it yet. Part #15-678.
The McKay-Dymek antennas are quite nice, too, but my C. Crane antenna
outperforms both of them. The DA-100D covers 50 kHz up to 30 MHz, so it may not be fair to compare it to antennas optimized for the broadcast band. It has the advantage of allowing remote location of the antenna whip to maximize signal to noise ratio and it offers two levels of attenuation (-10 dB and -20 dB) for
strong signals, as well as matching for 50, 100 and 500 ohm tuner impedances. There is an input for an auxiliary antenna in addtion to the whip. I haven't really gotten into listening to anything beyond the broadcast band yet, so I can't really evaluate its performance at other frequencies. There were a number of variations of this antenna produced over the years, starting with the DA100. The original version used a relatively large box with thick wood side panels for the control unit. At some point this was changed to a much smaller box with plastic side panels. The "D" version I have uses this smaller control unit. The antenna evolved up through at least an "E" version and there was also an "M"
(for Marine) version with a corrosion resistant whip. At some point in the evolution, connection for an external 12V DC power supply was also added (the "D" version includes this). At least some versions also omit the attenuator, impedance selection and the auxiliary antenna input.
The McKay-Dymek DA9 was (I think) the last of a series of four similar shielded ferrite rod antennas for indoor use. It was preceded by the DA3, DA5 and DA7. The DA9 covers up to 1900 kHz, wheras the DA3 and DA5 stopped at 1600 kHz. I'm not sure about the DA7. The ferrite bar is enclosed in a rectangular box on a short pole that plugs into the control unit and allows the bar to turn 360 degrees and tilt up to about 45 degrees. There were several different rod units produced. Mine is a DL4. I don't know what the differences were, but I think some did not have the oak trim that the DL4 has and I'm sure some of them did not cover frequencies up to 1900 kHz. The control unit appears to use the same box and wood side panels used for the early versions of the DA100 control box. Construction quality is really excellent and the unit has a classy look and feel to it. There is a large tuning knob with step-down gearing for easy fine tuning. The front panel also has a small, continuously variable 'Sensitivity' knob and an identical knob for power on/off. The Sensitivity control allows a large range of attenuation and amplification of the signal. The Sensitivity control and the very well-designed tuning knob make the DA9 the easiest of all these antennas to use. Because the antenna must be inside, it doesn't give me as much elimination of noise as the C. Crane, though. And the DA9 appears to resonate over a wider frequency band than the C. Crane, which has a very sharp tuning action that seems to more effectively eliminate interference from adjacent frequencies.
The McKay-Dymek ferrite bar antennas seem to usually sell for around $300 with a range from $200 - 350. They are pretty rare and apparently prized by collectors. I felt very lucky to pick up my DA9 for $115 on eBay. The power cord had been spliced, but it was otherwise perfect. In my experience so far, the C. Crane is a better performer for a fraction of the price, however and I can't really recommend the McKay-Dymeks at their normal selling prices. Even for the $115 I paid, I would keep the $70 C. Crane if I could only have one. It's possible I might change this opinion with longer-term use and more attempts to receive difficult signals, but so far, the C. Crane is the winner.
The lesson in all this for me is that the antenna is even more important for AM than for FM. Even the inexpensive Terk antenna made a huge difference in the performance of my AM tuners. Listening to a couple of the local AM stations that broadcast a high quality signal approaches the quality of FM. There is one local AM station (1460 KARR, Kirkland WA) that has a really great signal and uses minimal compression. I think I would rather listen to music broadcast by this station on AM than listen to the same music on some of the super-compressed FM stations in the area."
Jay Allen at radiointel.com has a great review of the Terk AM Advantage and a Select-A-Tenna, which is available in several different models.
More on AM Tuners
Here's Eli again with some thoughts on tuners for AM: "My personal favorites, both for sound quality and reception on the AM band, are (starting with the best):
E.H. Scott 800-B tube behemoth (reception not as good as those above,
but has a very "euphonic" sound)
Having wide and narrow bandwidth switching on an AM tuner can really help with noise reduction when reception is compromised and with getting the best sound when reception is clear. A lot of the better tube tuners have this feature. On most newer AM/FM tuners the Wide/Narrow switching applies only to the FM band, but there are a few on which the wide/narrow switch works on AM, too. Some are listed in the reviews on fmtunerinfo.com. Neither Yamaha has this feature (the Dymek does) but the Yamahas sound very good, anyway. Very detailed, with well-chosen bandwidth to balance sound quality and noise in a way that works well in today's environment (crowded band and lots of noise sources)."
And John Byrns adds: "The king of AM-only tuners from the 'high fidelity' era was the Fisher AM-80, one of which I have in my tuner collection. This tuner is the ultimate AM-only tuner from the era, in the same way that the REL Precedent is considered the ultimate FM tuner from the 'high fidelity' era. The AM-80 features a tuned RF stage and two IF stages with three choices of IF selectivity. This tuner is extremely rare and hard to find. My solid state AM-only tuner is the Radio Shack TM-152 which I find more than adequate for my AM reception needs, although the stereo feature has become useless due to the advance of technology. I highly recommend this tuner for trouble-free AM reception if solid state is acceptable."