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article number 731
article date 08-16-2018
copyright 2018 by Author else SaltOfAmerica
Is Radio Coming of Age?, 1922 - Part 3: Hobbyists Learn Radio
by Various Popular Science Magazine Writers

“As Easy as ABC!”

By Jack Binns

I HAPPENED to be in a radio store the other day, and I overheard a young woman turn to a girl companion, and exclaim:

“Really, Blanche, it’s foolish to buy one of these radio phones. We’ll never be able to use it. Just listen to those awful names we’ve got to learn!”At the same moment, an ardent young amateur was asking a bewildered new salesman whether he thought a variocoupler and tickler were better for a regenerative set than a variocoupler and two variometers, and wouldn’t three honeycomb coils be the best of all? He was also inquiring how many microfarads capacity the secondary oscillating circuit condenser should have.

I listened with a great deal of interest, because I realized that just such situations as this might be, even now, profoundly discouraging thousands of potential radio fans. And my mind reverted to an incident of the previous week, when, with Louis Pacent and “Ed” Glavin, inventor of the radio-controlled automobile, I had acted as a judge in a radio competition in Newark, N. J. One of the prizes in this competition was for the best homemade receiving set, using homemade parts exclusively. The competitors were all boys under 14 years of age.

The boy who was adjudged the winner had made a perfectly good working set out of a wooden soapbox. He had wound his coils around two breakfast-food cardboard boxes. His condenser consisted of a number of metal plates, spaced apart with washers. The detector was contained in a thimble, and the contact for it consisted of an ordinary safety-pin. This crude set, made up of odds and ends from the pantry and dressing-table, received music perfectly.

Don’t Let Terms Scare You

I do not think anything better illustrates the simplicity of radio. Don’t be frightened by the technical terms that are applied to various apparatus. You’ll Soon learn that the things they describe are simple bits of wire, or plates of metal. Scientists have applied the technical terms simply for their own convenience.

Radio is an infinitely bewildering mystery—but you don’t need to solve it to enjoy it. In fact within the next six months the radio receiving apparatus will be so simple that only one adjustment will be necessary, and any child can work it.

Wireless in the Home. An interesting book written in a non technical language for the many buying a small Radiophone Receiving Set to listen to Opera, News, Reports, Lectures, Concerts, etc. by Lee DeForest, Ph.D., D.sc., the world’s foremost inventor and pioneer in the Radio field. DeForest Radio Tel. & Tel Co. 1391 Sedgwick Ave, New York.

Radio Store Provides Free Clubroom for Wireless Amateurs

IN THE BACK of a retail electrical store located in the skyscraper section of New York City, there is a unique clubroom for radio amateurs. A full set of radio receiving equipment has been installed with an aerial on the roof. Apparatus can be tested out in actual practice, and the visiting amateur is given the privilege of taking any piece of apparatus from stock to connect up and use as he sees fit.

The employees of the store make no attempt whatever to sell goods to the amateurs using the clubroom. Even if the visitor asks for information, it is given without any intimation that he is expected to buy.

Amateurs who live many miles apart and who know each other only via wireless, form a habit of dropping into the club and talking over their installations. If one has a new idea in hook-ups, there is a chance to test it out. If a newcomer wishes to learn the standard connections, there are blueprints on the walls.

If a “club member” has a theory of radio to demonstrate, he can step to the blackboard and sketch it out with the other amateurs present giving criticism arid argument.

Sometimes, if one is lucky, one may meet some of the experts from the big wireless companies, and get the latest “dope” direct.

By promoting interest in radio, the clubroom has proved a moneymaker for the store. The goods sell themselves, for by listening to the conversations in the clubroom the beginner in wireless finds out what he needs for a first class station, and goes out into the store and buys it. He has learned the right name, too and does not waste the clerks time nor compel the salesman to give a curtain lecture on electricity and magnetism every time a receiver is sold.

Best of all, the clubroom gives the amateurs a chance to exchange ideas and stimulates their interest in radio.

In this unique radio store, amateurs may take any piece of equipment from the shelves and carry it to the clubroom in the rear. An aerial is provided so that amateurs can test their sets.

Government Experts Tell How to Make a Radio Set for $10

By Franklin S. Keating

TEN dollars, according to wireless experts in the Bureau of Standards, will build a receiving set that will permit an amateur to listen in on signal, from navy stations 200 miles away and from broadcasting stations 25 miles distant. The set is one that can be built at home. the final cost depending on the cleverness of the worker with the tools and materials available.

The knowledge of radio gained in the construction and operation of this set will form a sound basis for later sets of greater power and receiving range.—THE EDITOR.

—YOU can build a $10 radio set, consisting of tuning coil, crystal detector, and phone, as planned by government wireless experts, by following these detailed directions.

For the tuner secure a cardboard tube 4 in. in diameter. The cores around which linoleum is wound are ideal for this purpose and can usually be obtained free at a house-furnishing store. If not procurable there, the round cardboard boxes of certain kinds of breakfast foods, while thinner, can be used if handled carefully.

For the coil secure 1/2 lb. No. 24 double cotton-covered copper wire. If this size is not available, the next size above or below will make but little difference. Beginning at a point 1/2 in. from one end of the tube, punch two holes through the cardboard. Put one end of the wire down through one hole and up through the other, until the end is firmly anchored, leaving about 12 in. for the connections.

Wind on 10 turns of wire tightly and closely, and then, while holding the turns. arrange a loop for a tap. Do this by punching two holes, as at the beginning, and passing down and up through them a 6-in, loop of the wire.

With this done, wind on 10 more turns and take off another loop. But instead of taking of taking off the second loop directly beneath the first, “stagger” it about 1/2 in. This makes it easier to carry the connections to the switch points without short circuiting them.

Continue winding In the same manner until the seventieth turn, making six taps in all. Then, commencing with the seventy-first turn and continuing for 10 turns, take off a tap from each turn.

At the last tap, anchor the wire firmly, leave 12 in. for the end connection, and cut the wire from the spool.

Bureau of Standard’s crystal set.

Use Brass Screws for Switches

Now lay the tuner aside while the other parts are finished. Secure a piece of wood 1/2 in. thick, 5 in. wide and 8 in. long to be used as the panel.

Remove two birding posts from old dry cells and attach to the panel at points 2 in. apart.

Drill the first hole for the top binding post in. from the top and in. from the left-hand edge.

Next, lay out the two switches with their handles and the necessary switch points. For the handles, drill two holes at the same height as the lower left-hand binding post, 3 and 6 in. respectively from the left-hand side. With these holes as a center, draw a circle 1 1/2 in. in radius to locate the switch points.

Switch points can be made by taking 18 3/4-in round head brass screws and filing the heads down to a flat surface. They are inserted in holes drilled along the circle, separated by a distance equal to the diameter of the head.

The taps taken from the single turns are fastened to the left-hand switch and those from the “tenth” turns to the switch on the right.

The switch arms or handles may be purchased from a supply store or can be made by sawing a slice from a broom handle with a piece of brass rod or bolt passing through the wood to the back of the panel. The brass contact can be cut to shape and fastened to the under side of the piece of wood in such a way as to make contact with the bolt.

The wiring of the panel is then completed by carrying a wire from the ground binding post—the lower one—to the left-hand switch arm, and connecting the upper binding post—the aerial—to the right-hand switch arm.

All that now remains are the detector, condenser, and the binding posts for the telephone.

The detector consists of a piece of galena held securely by wood screws to the base and a fine spring wire attached to a movable arm so that the position of the wire can be changed.

The spring wire—an E mandolin string may be used—is wound several times around a small finishing nail after the latter has been slipped through the binding posts.

A piece of cork or wood may be used for the knob of the detector or a very good handle can be made by softening sealing-wax and molding it to the desired shape before it hardens.

Attach the detector on the extension of the base near the back and the two binding posts for the phone near the front edge.

Complete the wiring for the set by connecting the ground binding post with the left phone binding post and the antenna post with one side of the detector.

Connect the other side of the detector with the remaining post of the phones and the work is done.

While not necessary to the operation of the set, a fixed condenser placed across the phones will bring in the signals clearer and slightly louder. It is simply made.

Obtain some tinfoil and waxed paper. Cut four sheets of the tinfoil 4 by 3 in. and the waxed paper 4 3/4 by 3 3/4 in. Lay down a sheet of the paper and in the center of it place a sheet of the foil, holding the latter in place by a drop of shellac.

Connect the tinfoil with the outside by small strips of the same material 2 by 1/2 in., placing them alternately at one corner and then the other, so that after laying down the four sheets of tinfoil and five sheets of waxed paper, there will be two sets of connections.

Place a piece of stiff cardboard on top and bottom and bind the whole with tape.

Fasten each set of connections together and lay them under the binding posts for the phones.

A single phone receiver can be purchased for as low as 65 cents, but for best results a Baldwin phone costing about $6 should be used with the outfit. This is the most expensive part of the set, but is well worth the cost.

A test buzzer is a worthy addition to any set. Connect a dry cell with an ordinary doorbell — with bell removed — and a homemade switch of any kind. Lead a wire from the vibrating point of the bell to the ground wire and attach it there.

DIAGRAM-Buzzer set.

If the crystal is in good adjustment, a loud buzz will be heard in the phones when the buzzer is operated. If the buzz is heard in the set, then wireless signals within the range of the set will also be heard.

In constructing the aerial, height and length are the factors that affect the receiving distance. An aerial 60 ft. high is twice as good as one only 40 ft. high. The single wire of No. 14 bare copper should be made as long as possible, preferably over 100 ft.

It is not necessary that both ends be of the same height. If the end farthest from the house can be attached to a tree or mast, the lower end can be sloped so that it leads directly to the instruments.

The principal parts with their costs are as follows:

• Wire No.24 — $0.75
• Cardboard tube — .10
• Switch bolts and nuts — .25
• Galena crystal — .25
• Test buzzer — .50
• Dry battery — .30
• Rope for aerial — .50
• No. 14 wire for aerial — .75
• Pulleys for aerial — .39
• Insulators — .20
• Tinfoil — .10
• Phones. — 4.50

Nature’s Electric Valve

By Jack Binns

WHAT is a crystal detector? Of what does it consist and how does it work?

Since the advent of radio-telephone concerts, the answer to this question is bound up in the story of galena and its properties. Galena is an ore of lead, consisting of lead sulphide. It is in the crystalline form that this ore is best known to the wireless amateur and novice, although it has been known to man since the time of Pliny, the Roman naturalist.

Now galena, when placed in an electric circuit, has the remarkable and valuable property of rectification, or, in other words, it will permit a current to flow through it in only one direction. It completely checks the opposing current.

Rapid Alternations

This is a property that is urgently needed in wireless circuits, which deal exclusively with very high-frequency alternating currents. In fact, the frequency of the average radio currents received from the broadcasting stations throughout the country is at the rate of 833,333 cycles a second; which means that the current changes direction, or, in more exact terms, changes from positive to negative—at the rate of 1,666,666 times a second.

These current changes are so rapid that they exert an equal, pull in either direction on the telephone diaphragm, and consequently the telephone would not respond to them.

Now, if we can eliminate one half of them, say the positive half, and allow only the negative half to flow through the telephone, we shall hear the radio signals.

Galena does just that. It performs its duty in exactly the same manner that a valve works in a waterpipe system. It permits the current to flow forward through the circuit, and stops any back flow . . .

. . . in other words, it transforms alternating current—which flows rapidly in both directions—into pulsating current flowing in only one direction, and thus enables the telephone to record what is passing through the air.

For the purposes of wireless telegraphy, galena is a very sensitive detector, but for radio-phone work it is not reliable at a greater distance than 25 miles.

I have often been asked if there is any other crystal just as good. The answer IS, no. The element silicon is almost as good, and the combination of zincite-bornite is not bad, but neither element equals galena.

The Marvel of Wireless. To know that you can receive wireless telephone, music and speech right in your own home is in itself wonderful—but to be able to do this for the small amount of $15 make it most wonderful. This is the very thing you can do if you live within 30 miles of a broadcasting station, with a Marvel wireless telephone outfit for $15 complete.

Remember—reputation and a guarantee of dependability are built into every Freed-Eisemann unit by the same engineering skill that designed radio apparatus now used by the U.S. Navy. Freed-Eisemann Radio Corporation, 255 Fourth Avenue, New York City.

Four Ways to Erect an Aerial for Your Radio Receiving Set

by Louis S. McNamara.

THERE are two main points to be considered in laying out and constructing an aerial. They are: Make it as high as possible and as near 125 ft. in length as facilities will permit. One wire will do as well as two or more.

The exact manner of erecting the radio aerial will depend on the location of near-by objects from which the wire can be strung.

A tree is perhaps the most accessible of anchorages for aerials, but to get best results a mast should be erected in the top of the tree in order to elevate the aerial above all branches. If this is not possible, the aerial can be swung from one of the branches, providing the wire is well insulated from the tree.

Next to a tree a wooden mast, made by nailing together two 2 by 4’s to form a 4 by 4, makes a good aerial post. Two sections, each 20 ft. long, with a 3-ft. splice, will give a mast about 30 ft. high. Such a mast should be prevented from buckling by 3 guy wires attached at or near the splice, although this is not essential if the mast is in a protected place or if the wire span is not long.

But the best aerial mast of all, the most easily erected and the most permanent, is the pipe mast. This can be lifted to any height, providing the bottom section selected is large enough and that plenty of guys are used.

In making a pipe mast the height will determine the size of the bottom section. If a height of about 35 ft. is desired, start with a 2-in, pipe as in the illustration. At one end screw on a pipe cross and in each of the side taps screw a plug with a 1/4-in. hole drilled in its head. At the remaining open tap put in a 2- to 1 3/4-in. reducer for the next section of pipe. The holes in the plugs are for the guy wires.

By thus reducing the size of the pipe in each successive section, the aerial mast may be carried up until the final section is 3/4 in. in diameter. All bending strains will be taken up by the guy wires.

The bottom section should be embedded for about 18 in. in solid concrete and the whole pipe well covered with red lead to prevent rusting. If galvanized pipe is used it need not be painted.

The presence of so many guys is an asset to any station. Each guy wire should be insulated at top and bottom by a simple corrugated strain insulator. Then, if desired, all the wires can he connected with one lead-in wire, thus making a secondary aerial. This secondary aerial could be connected with a switch inside the receiving station for use when stations with longer wave lengths are to be tuned in.

Radio amateurs who live on farms where windmills are used for water pumping are already supplied with an excellent antenna mast. One end of the aerial can he fastened to the top platform of the mill: and the other carried to a hook on the house near the instruments, which completes the aerial.

On all the foregoing types of aerial suspensions, with the exceptions of the tree and windmill anchorages, a pulley should be provided for lifting and lowering the wire. A galvanized metal pulley and a 3/8-in. rope will be sufficient.

The rope will last longer if it is tarred, but as the expense of tarring will nearly equal the cost of new rope, the advantage is somewhat doubtful.

Four ways to erect an antenna.

How You Can Receive Radio Messages with a Bit of Wire Fencing

Odd Experiments with New Wireless Antenna that Is Inexpensive and Requires No Ground.

By Armstrong Perry

TWO pieces of chicken wire, stretched horizontally between two insulated supports, have been found by the Bureau of Standards to possess all the advantages of the loop antenna without several of the latter’s disadvantages. With this a reality, one of the last obstacles to a wider participation in radio enjoyment by the amateurs of America has been surmounted.

According to Hiram Percy Maxim, there are over 250,000 radio amateurs already receiving benefit from the increased activity in wireless. Football and baseball scores, weather forecasts, market reports, election returns, the correct time, and general news from all parts of the world, are some of the items picked up daily by the quarter million radio enthusiasts.

And that does not complete the list by any means. Radio concerts, both vocal and instrumental, are being given with semi-weekly regularity. In some sections of the country sermons and church music are delivered broadcast to whosoever has a radio receiving station to catch and enjoy them.

Construction of Loop Antenna

It was only a short time ago that a receiving outfit was designed so sensitive that a loop of wire four feet square would gather enough energy to render sounds perfectly clear in the ear of the receiver.

The heart of this set was an audion bulb or vacuum tube that looks like an electric-light bulb, but contains in addition to the filament two other metal parts called the grid and plate.

By turning electric currents of different voltages into the filament and plate and passing energy gathered from the intercepted radio waves through the bulb, the electrical waves sent out by the transmitting station are translated into intelligible sounds exactly similar to those made at the sending station, whether they were in the form of music, conversation, or the dots and dashes of the Morse code.

Yet the loop antenna had certain drawbacks. It was difficult to make, and after completion it had to be handled with great care lest the turns of wire became bent or jammed. In dismantling for storage, the task of unwinding the coils of wire was a tedious one.

Undoubtedly with these facts in mind, the Bureau of Standards has developed the condenser antenna working on a principle different from that of either the loop or straight-wire antenna.

Those who have already taken their first steps in radio know that the receiving station must be “tuned” to the transmitting station that it is desired to hear.

This tuning is accomplished by a balancing of two electrical properties— inductance and capacity. Inductance always lags and capacity rushes ahead. The radio amateur merely turns the two or three knobs attached to his apparatus and gets the results whether he knows what is happening inside or not.

The loop antenna has a large value of inductance that is balanced by the capacity of condensers in the tuning apparatus, whereas the condenser antenna has a large value of capacity and is balanced by the inductance of wire coils in the tuning apparatus.

But this difference means less to the average amateur than the fact that he can readily make a condenser antenna out of two pieces of chicken wire or two window-screens or two anything that are flat and made of metal and that can be suspended parallel with each other with a reasonable amount of air space between.

The pictures on this page tell the story better than words. Wire netting of various sizes has been used varying from six feet up to thirteen feet square. These screens were suspended from a specially built frame, but they could be hung from trees or from the ceiling or from anything else as well, so long as they are insulated so that the energy that they pick up will all go into the receiver and none of it escape.

The author of this article tried out a condenser antenna made of two window-screens insulated with books. Immediately he heard a long-wave-length station, three hundred miles away.
Instrument layout used by the Bureau of Standards to test the adaptability of the condenser antenna made of fine-mesh copper screen. Half of the antenna is not included in the photograph.

Hanging the screens vertically instead of horizontally reduced the strength about 75 per cent.

It has been determined that the circuits used with an ordinary antenna are equally satisfactory with the condenser antenna. But for convenience and quick tuning a special circuit was devised that required but one adjustment for any given wave length after the vacuum-tube detector was set in operation.

No tests were made using the antenna for transmitting, but it should prove very effective because its low resistance permits the radiation of most of the energy generated.

It Has a Military Value

This new antenna may be found of the utmost importance in military operations. The work of unrolling two such screens as used in this experiment and making the necessary connections can be accomplished in a minute or two.

Like the loop antenna the condenser antenna requires no ground connection, which is an advantage, as a good “ground” is often difficult to find.

The investigators concluded that “the condenser antenna of small dimensions has a decided advantage over the coil antennas when wave lengths under 250 meters are employed,” but that the larger screens needed for successful reception of longer wave lengths would render the outfit less easily portable.

Using a Window-Screen Aerial

WHEN I HEARD of this condenser antenna, I set out at once to test it from the amateur’s standpoint. I yanked out a couple of ordinary japanned window-screens. One I laid on a pile of books on my study table. On top of this I piled more books and then laid the second screen on top of the heap. Then I scraped bare a small place on each screen and attached copper wires leading to my long-wave regenerative receiving-set.

“I adjusted the knob for 600 meters. Da de, de da, d’d’d’d. NAH, the New York navy radio station, was just signing off. It was fainter than it is when I receive it over my 110-foot single-wire antenna, but it was readable.

“Shifting my inductance switches, I went up to the extremely high waves. By turning one knob I could then cover a range of from 10,000 meters to 24,000 meters. An arc-station signal came whistling in, faint but clear. Soon I was able to identify it as coming from WSO, an experimental station at Marion, Massachusetts.”—Armstrong Perry.

Outfit Receives Continuous Wave Radio Signals

Being the Third Article on Wireless Receiving Sets by Arnold Holmes

SIMPLE wireless receivers and audion detectors and amplifiers, such as were described in detail in the December and February numbers of POPULAR SCIENCE MONTLHY, are capable of receiving only spark signals or modulated continuous wave signals.

That involves detection alone. Figure 1 illustrates the sort of voltage across the detector resulting from detection, which is, in effect, rectification. The current in the output of the detector is as shown.

The current through the telephones is the audio frequency current; that is, the frequency at which the amplitude of the radio frequency current and voltage vary. That variance is what makes spark signals and modulated signals audible by detection.

The question then arises, how are continuous wave signals made audible? Upon detection of continuous-wave telegraph signals direct current results. That, of course, is not audible in the telephone receivers except in the form of a click.

In order to make continuous-wave signals audible, another frequency generated by the receiver, which differs from the received signal by an audible frequency of perhaps one thousand cycles, is impressed on the detector together with the signal.

These two frequencies produce beats occurring at a frequency that is the difference between the signal and local frequency.

Upon the detection of this high-frequency voltage, whose amplitude varies at an audible rate, the low frequency is obtained that becomes audible in the telephone receiver.

What apparatus is needed to accomplish this? Figure 2 is a circuit diagram of a receiver that is arranged to receive continuous-wave signals. The local oscillations are produced in the circuit L2 C2 by the vacuum-tube oscillator, which is of the feed-back type.

Oscillations are produced in the circuit by feeding some of the amplified high frequency in the plate circuit of the tube back into the input. This is controlled by the coupling of the tickler coil (L3) with the secondary coil (L2).

A very convenient receiver for this range of wave lengths is illustrated in Figure 3 on the following page. The universal mounting shown allows the coupling to be varied between antenna and secondary circuit and between tickler coil, not only by moving the coils apart, but by actually rotating them 90 degrees with respect to each other. This provides a fine degree of variation of the coupling.

By the use of honeycomb or duo-lateral coils the wave length range of the set can be made almost anything.

The size of the coils that should be used may be determined from the accompanying list of the duo-lateral coils required to give a wave-length range of from 2000 to 15,000 meters, using a tuning condenser of from 50 to 1000 micro-microfarads (.00005 to .0010 microfarads).

Fig. 1. Diagram illustrating the transformation of signals at various stages between antenna and telephones.
Fig. 2. Wiring diagram for simple continuous wave receiver.
TABLE: Duo-lateral coils required to give a wave-length range of from 2000 to 15,000 meters, using a tuning condenser of from 50 to 1000 micro-microfarads (.00005 to .0010 microfarads). Primary Inductance, Tickler Coil, and Secondary Inductance for Antenna of 400 M-mfds.
Details of primary coil winding and coupling arrangement.
Details of secondary coil winding and coupling arrangement.

This receiver can be used with the detector amplifier described for the simple receiver by connecting the tickler coil to the proper binding-posts. In connecting the tickler coil, it should be remembered that it must be correctly poled.

The photograph shows a convenient and neat detector amplifier and cabinet. With this receiver the high-power transatlantic and transpacific stations, the naval stations, and most of the post-office stations engaged in sending out market reports can be copied.

A long-wave receiving set.

How I Made Bank-Wound Coils for Short-Wave Reception

HONEYCOMB, or lateral wound, tuning coils, have been found to be very efficient in all wave lengths above 450 meters and to give results on broadcasting waves equal to those obtained from the ordinary loose coupler or double glide tuner.

The common types of tuning devices are limited in their range, but the station equipped to use honeycomb coils can pick up messages from 200 meters to 20,000 meters merely by the substitution of proper coils in the coil mounting. It should be noted, however, that the honeycomb coils are covered by U. S. letters patent.

Front and side views of a bank-wound coil.

In winding my own coils I found that the size of wire makes little difference except as to the space taken up. Numbers 22, 24, or 26 wire will give equal results as far as an amateur can perceive. My coils for receiving broadcasts at 360 meters were made as follows:

I secured a wooden block that could be fitted tightly inside a pasteboard tube 2 in. in diameter. The pasteboard tube was cut to a width of 1 in.

After the tube had been slid over the block, I drilled a series of small holes, 1/4 in. apart, completely around the edge of the tube on both edges. Into these holes pegs or brads were driven, leaving them projecting about 1/2 in. The spacing of the pegs I found to be the same on all coils whatever their wave length, but the thickness of the winding varies with the amount of winding applied.

Front, side, and top views of coil mounting.

The coil was wound according to the winding diagram. I attached the end of the wire to one peg taken at random, counted off the eighth peg on the opposite side and carried the wire to that point. Then I counted off eight more on the starting side, led the wire to that, and so on.

Winding diagrams.

The pattern for each coil was arranged so that after each revolution of the winding the wire appeared at the peg just before the one used to start the preceding round.

This form of winding was continued layer upon layer until the desired length had been applied, which, in the of the broadcasting coil, was 155 ft. of No. 24 wire. The exact amount of wire needed, I found, depended on the aerial, the capacity of the condensers used, and other tuning devices, and the figures given above are approximate.

After the coil had been completed, it was well coated with the best quality of white shellac obtainable. I discovered it was better to leave the coil uncoated rather than use an inferior grade of shellac.

Finally the circular coil had to be arranged so that it could be plugged in or out of the coil mounting. To do this, I took a block of hard wood 1 1/2 in. by 1 in. by 1 1/8 in. and at a point in 5/8 from one flat side chamfered slightly to give a finished effect.

Then on the side opposite the chamfer I scribed an arc that agrees with the outer surface of the finished winding. I bored two 1/8-in. holes through each block and in the holes drove a piece of 1/8-in. brass rod. Then I rounded off one end and attached the ends of the coil winding to the other ends, as shown In the diagrams.

The coil blocks and the connections in coil mountings.

The coils were held rigidly to the coil block by zinc or brass saddles that passed up from the flat side of the
block, over and through the inside of the coil and down the other side of the block, where they were fastened.

Although not essential, an added finish was given to the coils by covering their outer surface with a strip of thin fiber board.

After the coils were completed, a mounting was provided so that the one coil could be substituted for the other in changing wave lengths and also in order that one coil could be swung sidewise for closer tuning.

These mountings I made to accommodate either two or three coils, according to the circuits in use.

For the two-coil mounting, said to be equal in its effects to a loose coupler, the drawings show the measurements and the method of assembly I used. I secured two pieces of hard wood, well dried, 2 1/2 in. by 1 1/2 in. and 1/2 in. thick.

One of these was for the permanent mount and the other the swinging mount.

I took two other pieces 2 3/8 in. by 1 1/2 in. by 1/4 in. thick for top and bottom supports and attached the coil mounts as shown in the drawing.

In one face of each of the mounts I bored two holes 3/16 in. in diameter completely through the wood. Then I obtained some short lengths of brass tubing, 3/16 in. outside diameter and 1/8 in. inside diameter and soldered a 2-in, length of flexible cord to each tube, inserting a tube in each of the four holes with the flexible cord leading toward the back.

A good assortment of these coils was assembled in my case by winding six or eight sets with a difference of five layers in each set. That is, in the broadcast coil just described about ten layers were needed.

With these coils I experimented until I found the proper combination for every station, whether It is an amateur of 200 meters or one of the transatlantic stations with 14,000 meters.

Using coil for loading.
Coils used for loading a loose-coupled circuit.

How to Make a Two-Stage Radio Receiving Set

By E. L. Bragdon

A Blueprint Will Help You Make a $125 Set for $40

THE article on this page is designed to be used with or without the blueprint of the receiving set prepared by the Home Workshop Service Department (see page 84), although to make his work as simple and certain as possible, the novice is advised to obtain the scale drawings.

In either case it should be kept in mind that the Information Department will answer any questions and make suggestions regarding the construction, assembly, and operation of the outfit.—Home Workshop Editor.

PROBABLY no one set has proved so successful in making the radio telephone live up to its prestige as the two-stage outfit. The audion detector is a big step beyond the crystal detector; the single stage of amplification somewhat steps-up the strength of signals, but the first big increase is noted when the second stage is added.

The amplification made possible by the two amplifying tubes seems to make up for the deficiencies in most amateur aerials and grounds.

Added to this is the remarkable selectivity possessed by the tuning circuits of these sets.

In the set about to be described the best features of several types of outfits have been incorporated, and in one particular—that of ample space to work in—the set will receive the commendations of any amateur fortunate enough to build one.

The steps followed in construction should be as follows:
• winding of variocoupler and variometers;
• making of supports for vacuum tubes;
• machining of bearings and pivot rods for coils;
• planning and bench work on panel front.

After finishing the panel unit, the set can be given an added value by enclosing it in a well made cabinet such as is described on the opposite page.

For the primary tubes for variocoupler and variometers secure a 15-in, length with a diameter of 4 in. These tubes can be of cardboard or fiber.

Cut the 15-in, length into three equal sections.

Take one of the tubes and, beginning at a point 2 in. from an end, wind on 80 turns of No. 20 double cotton-covered copper wire. Take off taps at every 10 turns up to the seventieth, and from then on take off taps at every turn. The single-turn taps will be connected with a “units” switch and the 10-turn taps with a multipleturn switch.

The rotors or secondaries can be made from 3 3/2-in. tubing, or ball rotors may be purchased ready for windings.

If cardboard tubing is used for the secondaries, secure an 8-in, length, and divide into three sections as before. On one of the sections wind 30 turns of No. 20 d.c.c. wire, winding 15 turns on each side of the center, leaving a full 34 in. between the two windings for the swivel rod. The secondary winding is continuous and no taps are taken off.

Variometers Are Simple to Make

A piece of 1/8-in. brass rod, 6 in. long and threaded for a 1/2 in. on one end will be needed for each of the three tuning coils.

The panel forms one bearing for this rod and the primary tube the other. Movement of the rotor is obtained by a simple wire key passing out of the tube through a hole in the brass rod and back into the tube again.

One end of the secondary winding may be soldered fast to the rod, using a piece of flexible wire or a motor brush “pigtail.” The other end should be carried, by means of a piece of insulated flexible wire, through the base of the primary tube.

The variometers are much simpler to construct, since the windings on both primary and secondary are continuous and there are no taps on either. The variometer windings differ from the variocoupler in the fact that the swivel rod passes between the windings on primary as well as secondary. Space should be allowed for this purpose.

On one of the 4-in, tubes, commencing at a point 2 in. from one end, wind 10 turns of No. 20 d.c.c.; anchor securely; cross the space allotted to the pivot rod, and continue with 10 turns on the other side. Wind both variometers alike.

Use either the 3 1/2-in. tubes for the secondaries or the ball-shaped rotors. Whichever is used, wind 15 turns on each side of the pivot rod.

Connect each primary with its corresponding secondary by a “pigtail.”

As previously done with the variocoupler, connect the spare end of the rotor to the rod that has been inserted in primary and secondary.

Best results with an amplifying set, inductively tuned as this one is, are obtainable if the two variometers are separated some distance. This can be easily accomplished by locating the variocoupler between them.

The “units” and “tens” taps are led to the switches, and care should be taken that they are attached in proper order. Although it makes no great difference, the standard practice is to arrange the tuning switches so that turns are added (wave length increased) by rotating handles in a clockwise direction.

When completed, the variocoupler and varjometers are mounted in place on the baseboard. By inserting a 3/8-in. piece, cut to circular shape to fit the bottom of the tubes and held there by brass tacks, the tubes themselves may be secured to the base by screws inserted from below.

Dials are not essential to the operation of any set, but they will be found handy in case the amateur keeps a “log book” and they do add to the appearance of the set. Combination knobs and dials can be purchased from any radio store.

There is little that the amateur can or should attempt to make in connection with the vacuum-tube end of his set. The few dollars more spent for factory-built apparatus will pay in the end.

For this part there will be needed a detector or soft tube and two amplifying or “hard” tubes. The two last-named tubes will require amplifying transformers and each of the tubes will need a grid condenser, preferably with grid leak.

By placing the three tubes in a row from front to back of the set and mounting them high to leave space beneath for condensers and transformers, the set is compressed without decreasing its receiving ability.

The uprights for the tube platform are made of strip brass 1 in. wide, bent in the shape of a U, 5 in. on the side and 4 1/2 in. on the top.

The open ends of the U are bent inward 1 1/2 in. to take a hole for the 3/16 in. brass bolts to the base. As a certain amount of spring is not undesirable, two of these supports will be sufficient. It is a good plan to insert small pieces of sponge rubber beneath the platform supports, if possible, to take up any vibrations from the outside.

Between the two supports lay a piece of well paraffined wood or bakelite, 1/2 in. thick and 4 in. wide. Brass machine screws hold this strip to the supports and the vacuum-tube sockets may be screwed down directly on it.

The amplifying transformer for each tube is fastened to the under side, permitting the shortest possible leads between tubes and transformers.

The grid condensers can be placed where they come most handily in the grid circuits.

The detector tube will require one rheostat and the two amplifiers another. These rheostats can be wound at home, but inasmuch as their design plays such an important part in the close regulation of the filament current and the consequent life of the tubes the amateur should buy them if possible. There are good types on the market in which the coils are embedded in the material composing the knob and dial. They are neat and easily attached. Other types are fastened to the back of the panel with a control rod passing through to the front.

Place Panel in Cabinet

For the sake of neatness, connections should be carried through the back or side, thus leaving the front for telephone and loud-speaker connections and instrument dials. Although the aerial and ground connections are frequently found on the front, they would give as good results hidden in the rear. If the set is placed in a cabinet, these little improvements can easily be carried out by making the back of the cabinet permanent and placing on it the binding posts for all external connections.

Either binding posts or jacks can be provided for telephone connections to the detector, first and second stage circuits.

Since this is an inductively coupled set, no air condenser has been arranged for. In the event that the natural wave length of the aerial is too great to admit of tuning to the short amateur waves, a variable condenser of about .001 mid. capacity Should be inserted in the ground connection.

In fact, the range of the entire set could be increased many hundred meters by arranging a variable condenser through a double-pole double-throw switch, so that the capacitance can be thrown either in series with the primary tuner or in shunt around it.

Voices thru the air. Enjoy the thrill of wireless telephone every day right in your own home. A.H. Corwin & Co. Dept. P5 Newark N.J.

Knobs Fitted to Honeycomb Coils Improve Radio Set

THOSE amateurs using honeycomb coils on homemade sets know from experience that to place the hand on them when receiving “kills” the wave length. This difficulty, which is due to the added capacity of the hand may be largely prevented merely by fitting a small knob on the front of each coil.

Take off the outside strip that runs around the coil by loosening both the screws that hold it in place. Then use the strip as a guide or template for cutting another strip from thick, oiled cardboard, such as often is used for cheap notebook covers.

Put this underneath the original strip and fasten a knob to both by means of glue and a small, flat-headed screw.

One of the hard rubber knobs on a discarded circular wall switch makes a good knob, as it is already tapped for a small screw.

If you have access to a lathe, make the knobs of hard rubber or wood, which looks nearly as well as rubber if given a coat of black lacquer. Put these knobs on your set of honeycombs and you’ll never take them off.—J. M. ROLSTON.

How the knobs are attached to the coil.

Your “Troubles” and Mine!

By Jack Binns

OF course it’s exasperating to have your set give you trouble right in the midst of some snappy musical selection that is being played or sung in the distant broadcasting station. But when this happens, don’t get sore and blame the apparatus, or say radio has been overboomed. In ninety cases out of a hundred, the fault does not lie with the set itself. In all probability, you have overlooked some minor adjustment.

Perhaps only those of us who suffered in the early days of wireless development realize what manufacturing miracles have been wrought in turning out the precise, finely tuned, simply adjusted radio sets you can buy to-day.

When I first started in wireless work, the only detector that existed was the coherer—and a lot of incoherent messages it brought me! It was a little glass tube, in which there were a number of iron filings between two silver plugs. This detector was placed directly in the secondary circuit, and when the electromagnetic waves were received on the aerial, why caused these filings to cohere and offer a path for a current from a local battery to pass through the local circuit and operate the recording device.

This little coherer was so sensitive that the vibration of the ship would operate it, and although I succeeded in working with one for a whole year, I never did really know whether I was getting wireless signals from some other ship, or just listening to our own ship’s complaints about the weather!

At that, these meaningless messages tapped off on the tape by the vessel’s vibrations were interesting, because they broke up the monotony of the pioneer wireless operator’s life. There were probably only a dozen or so radio-equipped ships—and the chances for any conversations among them were rare.

The ether was, to all intents, one great silence. And that was only 18 years ago!

Later came the magnetic and crystal types of detectors, and with them a multitude of instruments, every one of which was variable and had to be adjusted and readjusted. The operation and appearance of a station became infinitely more puzzling to the layman than all the rest of the ship’s mechanism combined.

At that time, for instance, an inductance coil was a very imposing thing, perhaps five feet high and six inches in diameter. Now, a coil doing exactly the same work is not more than two inches in diameter, and one inch high!

This is a sample of the simplicity in design that has been achieved throughout the sets you now are using.

So, when you are turning your tuner knob and tickler knob, and think you have a lot of complex tinkering to do, give a thought to the days when one had to make more than a dozen skilled adjustments.

"Dear Bob: Jack and I are giving a Radio dance Friday. We want you and Alice to be sure to come. Helen."

Entertain Your Friends with Radio Music. Every day there are radio concerts. Dance music and vocal selections, classical music and the latest popular "hits" are being sent out regularly by radio-telephone.

To get good results with a wireless telephone you must have a reliable battery. The Willard All-Rubber Battery has back of it the same long battery experience, and is built to the same standards as the Willard Threaded Rubber Automobile Battery, which is now standard equipment on 191 makes of cars and trucks.

Willard Storage Battery Company, Cleveland, Ohio.
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