Most of the radio stations listed in the cover and text illustrations would have been familiar to readers located in the northeastern United States at the time this article appeared. Four stations were Westinghouse facilities -- KDKA, Pittsburgh, Pennsylvania, WJZ, Newark, New Jersey, KYW, Chicago, Illinois, plus WBZ, Springfield, Massachusetts. Also included were a couple Department Store stations -- WOR, operated by Bambergers in Newark, and WWZ, owned by Wanamaker in New York City. WVP was a longwave station operated by the U.S. Army Signal Corps on Bedloe's Island in New York harbor.

WVP soon ceased entertainment programs, and WWZ expired in 1923, but the other five survive to this day, although WJZ is now WABC in New York, WBZ moved to Boston, WOR migrated from Newark to New York City, and KYW made a long-distance move from Chicago to Philadelphia.

The program guide illustration also includes WGY, General Electric's station then -- and now -- in Schenectady, New York. However, two call letters are mysteries -- WYC on the cover, and WYZ in the text illustration -- as these calls were never assigned to any broadcasting stations, and in fact according to records from this time period were actually assigned to two ships. Finally, there is no evidence that the Slot Machine Radio described in this article ever actually went into commercial production.

Science and Invention, September, 1922, pages 442, 515:

The  Slot-Machine  Radio
cover illustration
text illustration
With the Rapid Advance in Radio Design, We Shall Shortly See This Coin-in-the-Slot Radio Receiver Installed in Hotels, Railroad Stations, and Other Public Places. All One Has to Do to Enjoy Any Variety of Music or Speeches Desired, is to Drop a Coin in the Slot, and Then Turn the Knob Until the Call Letters of the Station Which is to be Listened to Corresponds With the Index Pointer Shown, Which Turns the Geared Loop Aerial Toward the Selected Station. The Apparatus is Entirely Automatic and Operates From the 110-Volt Lighting Circuit Without any Batteries, as Described in the Radio Department of this Issue. Four of the Vacuum Tubes Shown are Ballast Tubes, Which Automatically Regulate the Filament Current to the Four Detector and Amplifying Audions, in Place of the Usual Hand-Operated Rheostats. The Audions are Lighted When the Coin is Deposited in the Slot. The Apparatus is Self-Contained and Easily Made Fool-Proof With the Present Knowledge of the Art.
THE radio science is moving so rapidly these days that it is difficult to keep abreast of all its achievements. Moreover, we have become hardened to all the new wonders that are brought about by radio and we merely shrug our shoulders today when another development comes along. The latest addition to the radio family is a slot machine radio, which is now being developed by an eastern manufacturer. There was no reason, of course, that a radio slot machine could not have been built and manufactured for actual use five or more years ago. There was no demand for such a machine and none was produced. Today everyone is interested in radio, and with entertainments, from grand opera down to reports of prize fighting being broadcasted all over the country, such a machine is needed and demanded by the public.
    There are, of course, various ways of constructing such a machine, and one example of its construction is shown in our illustration.
    If a machine of this kind is to be used in any great quantity, for instance one in every suite of a 2,000-room hotel, the problem becomes complicated. In the first place, it is not possible to have an outdoor aerial for each outfit. Imagine the roof of one of our large hostelries equipped with 2,000 aerials! Plainly, such an idea, on its face, is preposterous. It therefore follows that we must use the loop system.
    On the other hand, every radio receiving set is also a radio sending outfit, as is well known, and unless the correct steps are taken every loop will send out a wave of its own, interfering with other outfits nearby. By a correct filtering system, however, this can be done away with in such a way that there will be little interference between the various receiving outfits. Also the smaller the loop used, the less will be the interference between the different outfits. The small loop, as shown in our illustration, as well as on our front cover, would perhaps be ideal for work of this kind.
    One of the most important points to remember in an appliance of this kind is that it must be fool-proof, and it must also be thoroughly practical. There must not be more than one knob or handle, and the adjustments must be all fixed in such a manner that the user will not have to change them once the set has started operating. Our illustration shows how this can be accomplished. In the first place, we have no batteries, either "A" or "B." The circuit is taken off a 110-volt lighting circuit, which may be either A. C. or D. C. If it is A. C., we need a transformer, as shown. We also need the rectifier tubes shown, which in a sense represent the "B" batteries. This system has actually been tested out by the Bureau of Standards, and it works. As for the arrangement of the circuits, we need not go very deep into this, for the reason that there are a number of hook-ups, and with a set of this kind we need at least six vacuum tubes, on account of the small loop used.
    The usual amplifying transformers and condensers (variable as well as fixed), can be seen in the illustration. A loud-speaking telephone receiver, as, for instance, the Baldwin type C, or any other similar means, can be used to connect with the lower horn from which the music or entertainment issues.
    The tuning inductance shown is, of course, set and fixed when the instrument is first installed. There are, however, a number of taps left in order to make changes when new stations come into use, or if the wave lengths are changed. The Company's Maintenance Department would have to take charge of these things.
    We now come to an interesting means proposed by the author, and which shows how, by a very simple method the loop can be turned by a center knob, and a certain amount of tuning done, all simultaneously. It is a well-known fact that if you receive from one station and then turn the loop to receive from another, a certain amount of tuning must be done; otherwise the entertainment will not come in at maximum strength. Very often the familiar whistling sound may be set up, which can not be avoided unless some tuning is done. The writer proposes to connect to the loop, by means of gearing, a sort of vernier condenser, which is placed in the circuit. This condenser is again geared, as shown, then by turning the front dial through quite a large angle, the shaft of the condenser will turn only a very small amount. Of course, the ratio of gearing has to be ascertained by experiments, as well as the positions of the stations plotted on the indicating dial. In practice, therefore, the dial would very likely be blank when the set leaves the factory. The Maintenance Department, when installing the outfit would then listen in for, let us say, WJZ. They would find a point where this station would come in loudest. They would then engrave the dial at this point with the call letters of that station, namely WJZ. Similar engraving would be done for other stations, so that the user of the instrument would have only to turn the knob to find the correct station, and where it would then come in at its maximum strength.
    As for the slot-machine operation, this is accomplished as follows: For an entertainment of this kind we may assume that 25 cents for a duration of two hours would not be too much, and would not be objected to by the user of the machine. A hotel guest, let us say, consults his paper and finds out that a certain station is sending, at 8:00 P. M., an entertainment in which he is interested. He puts the quarter into the slot, and for 25 cents he gets a two-hour entertainment. A clock dial is shown on the face of the instrument, and this operates in such a manner that it automatically cuts off the circuit when the second hour is reached. The user, by looking at the clock, can see how long the entertainment will last; then, if he wishes to have more than two hours, a new payment is to be made.
    Contrary to popular belief, a machine of this kind is not very expensive, and if produced in quantities it is possible to manufacture such an instrument for $100.00 or less.
    A slot-machine radio outfit, as here described, is one way of purveying radio entertainment to the public, and when it comes to hotels there is another method which might be found very desirable, especially in the better class of hostelries; namely, to make a slight extra charge on the price of a room, where the radiophone is to be used, and either a special key to unlock the main radio circuit switch could be furnished the guest when he registered at the hotel, or the sets might be locked and unlocked electrically from the clerk's desk.
    No doubt, this radiophone instrument will later be arranged for carrying on wireless conversation with subscribers in other cities, when the radio telephone comes into use.