As inferred in the first chapter, an aerial for receiving does not have to be nearly as well made or put up as one for sending. But this does not mean that you can slipshod the construction and installation of it, for however simple it is, the job must be done right and in this case it is as easy to do it right as wrong.

To send wireless telegraph and telephone messages to the greatest distances and to receive them as distinctly as possible from the greatest distances you must use for your aerial (1) copper or aluminum wire, (2) two or more wires, (3) have them the proper length, (4) have them as high in the air as you can, (5) have them well apart from each other, and (6) have them well insulated from their supports. If you live in a flat building or an apartment house you can string your aerial wires from one edge of the roof to the other and support them by wooden stays as high above it as may be convenient.

Should you live in a detached house in the city you can usually get your next-door neighbor to let you fasten one end of the aerial to his house and this will give you a good stretch and a fairly high aerial. In the country you can stretch your wires between the house and barn or the windmill. From this you will see that no matter where you live you can nearly always find ways and means of putting up an aerial that will serve your needs without going to the expense of erecting a mast.

Kinds of Aerial Wire Systems.--An amateur wireless aerial can be anywhere from 25 feet to 100 feet long and if you can get a stretch of the latter length and a height of from 30 to 75 feet you will have one with which you can receive a thousand miles or more and send out as much energy as the government will allow you to send.

The kind of an aerial that gives the best results is one whose wire, or wires, are horizontal, that is, parallel with the earth under it as shown at A in Fig. 3. If only one end can be fixed to some elevated support then you can secure the other end to a post in the ground, but the slope of the aerial should not be more than 30 or 35 degrees from the horizontal at most as shown at B.(A) Fig. 3.--Flat top, or Horizontal Aerial. (B) Fig. 3.--Inclined Aerial.

The leading-in wire, that is, the wire that leads from and joins the aerial wire with your sending and receiving set, can be connected to the aerial anywhere it is most convenient to do so, but the best results are had when it is connected to one end as shown at A in Fig. 4, in which case it is called an inverted L aerial, or when it is connected to it at the middle as shown at B, when it is called a T aerial. The leading-in wire must be carefully insulated from the outside of the building and also where it passes through it to the inside. This is done by means of an insulating tube known as a leading-in insulator, or bulkhead insulator as it is sometimes called.(A) Fig. 4.--Inverted L Aerial. (B) Fig. 4.--T Aerial.

As a protection against lightning burning out your instruments you can use either: (1) an air-gap lightning arrester, (2) a vacuum tube protector, or (3) a lightning switch, which is better. Whichever of these devices is used it is connected in between the aerial and an outside ground wire so that a direct circuit to the earth will be provided at all times except when you are sending or receiving. So your aerial instead of being a menace really acts during an electrical storm like a lightning rod and it is therefore a real protection. The air-gap and vacuum tube lightning arresters are little devices that can be used only where you are going to receive, while the lightning switch must be used where you are going to send; indeed, in some localities the Fire Underwriters require a large lightning switch to be used for receiving sets as well as sending sets.

How to Put Up a Cheap Receiving Aerial.--The kind of an aerial wire system you put up will depend, chiefly, on two things, and these are: (1) your pocketbook, and (2) the place where you live.

A Single Wire Aerial.--This is the simplest and cheapest kind of a receiving aerial that can be put up. The first thing to do is to find out the length of wire you need by measuring the span between the two points of support; then add a sufficient length for the leading-in wire and enough more to connect your receiving set with the radiator or water pipe.

You can use any size of copper or aluminum wire that is not smaller than No. 16 Brown and Sharpe gauge. When you buy the wire get also the following material: (1) two porcelain insulators as shown at A in Fig. 5; (2) three or four porcelain knob insulators, see B; (3) either (a) an air gap lightning arrester, see C, or (b) a lightning switch see D; (4) a leading-in porcelain tube insulator, see E, and (5) a ground clamp, see F.Fig. 5.--Material for a Simple Aerial Wire System.

To make the aerial slip each end of the wire through a hole in each insulator and twist it fast; next cut off and slip two more pieces of wire through the other holes in the insulators and twist them fast and then secure these to the supports at the ends of the building. Take the piece you are going to use for the leading-in wire, twist it around the aerial wire and solder it there when it will look like A in Fig. 6. Now if you intend to use the air gap lightning arrester fasten it to the wall of the building outside of your window, and bring the leading-in wire from the aerial to the top binding post of your arrester and keep it clear of everything as shown at B. If your aerial is on the roof and you have to bring the leading-in wire over the cornice or around a corner fix a porcelain knob insulator to the one or the other and fasten the wire to it.(A) Fig. 6.--Single Wire Aerial for Receiving. (B) Fig. 6.--Receiving Aerial with Air Gap Lightning Arrester. (C) Fig. 6.--Aerial with Lightning Switch.

Next bore a hole through the frame of the window at a point nearest your receiving set and push a porcelain tube 5/8 inch in diameter and 5 or 6 inches long, through it. Connect a length of wire to the top post of the arrester or just above it to the wire, run this through the leading-in insulator and connect it to the slider of your tuning coil. Screw the end of a piece of heavy copper wire to the lower post of the arrester and run it to the ground, on porcelain knobs if necessary, and solder it to an iron rod or pipe which you have driven into the earth. Finally connect the fixed terminal of your tuning coil with the water pipe or radiator inside of the house by means of the ground clamp as shown in the diagrammatic sketch at B in Fig. 6 and you are ready to tune in.

If you want to use a lightning switch instead of the air-gap arrester then fasten it to the outside wall instead of the latter and screw the free end of the leading-in wire from the aerial to the middle post of it as shown at C in Fig. 6. Run a wire from the top post through the leading-in insulator and connect it with the slider of your tuning coil. Next screw one end of a length of heavy copper wire to the lower post of the aerial switch and run it to an iron pipe in the ground as described above in connection with the spark-gap lightning arrester; then connect the fixed terminal of your tuning coil with the radiator or water pipe and your aerial wire system will be complete as shown at C in Fig. 6.

A Two-wire Aerial.--An aerial with two wires will give better results than a single wire and three wires are better than two, but you must keep them well apart. To put up a two-wire aerial get (1) enough No. 16, or preferably No. 14, solid or stranded copper or aluminum wire, (2) four porcelain insulators, see B in Fig. 5, and (3) two sticks about 1 inch thick, 3 inches wide and 3 or 4 feet long, for the spreaders, and bore 1/8-inch hole through each end of each one. Now twist the ends of the wires to the insulators and then cut off four pieces of wire about 6 feet long and run them through the holes in the wood spreaders. Finally twist the ends of each pair of short wires to the free ends of the insulators and then twist the free ends of the wires together.

For the leading-in wire that goes to the lightning switch take two lengths of wire and twist one end of each one around the aerial wires and solder them there. Twist the short wire around the long wire and solder this joint also when the aerial will look like Fig. 7. Bring the free end of the leading-in wire down to the middle post of the lightning switch and fasten it there and connect up the receiver to it and the ground as described under the caption of A Single Wire Aerial.Fig. 7.--Two Wire Aerial.

Connecting in the Ground.--If there is a gas or water system or a steam-heating plant in your house you can make your ground connection by clamping a ground clamp to the nearest pipe as has been previously described. Connect a length of bare or insulated copper wire with it and bring this up to the table on which you have your receiving set. If there are no grounded pipes available then you will have to make a good ground which we shall describe presently and lead the ground wire from your receiving set out of the window and down to it.

How to Put Up a Good Aerial.--While you can use the cheap aerial already described for a small spark-coil sending set you should have a better insulated one for a 1/2 or a 1 kilowatt transformer set. The cost for the materials for a good aerial is small and when properly made and well insulated it will give results that are all out of proportion to the cost of it.

An Inexpensive Good Aerial.--A far better aerial, because it is more highly insulated, can be made by using midget insulators instead of the porcelain insulators described under the caption of A Single Wire Aerial and using a small electrose leading-in insulator instead of the porcelain bushing. This makes a good sending aerial for small sets as well as a good receiving aerial.

The Best Aerial that Can Be Made.--To make this aerial get the following material together: (1) enough stranded or braided wire for three or four lengths of parallel wires, according to the number you want to use (2) six or eight electrose ball insulators, see B, Fig. 8; (3) two 5-inch or 10-inch electrose strain insulators, see C; (4) six or eight S-hooks, see D; one large withe with one eye for middle of end spreader, see E; (6) two smaller withes with one eye each for end spreader, see E; (7) two still smaller withes, with two eyes each for the ends of the end spreaders, see E (8) two thimbles, see F, for 1/4-inch wire cable; (9) six or eight hard rubber tubes or bushings as shown at G; and (10) two end spreaders, see H; one middle spreader, see I; and one leading-in spreader, see J.(A) Fig. 8--Part of a Good Aerial. (B) Fig. 8.--The Spreaders.

For this aerial any one of a number of kinds of wire can be used and among these are (a) stranded copper wire; (b) braided copper wire; (c) stranded silicon bronze wire, and (d) stranded phosphor bronze wire. Stranded and braided copper wire is very flexible as it is formed of seven strands of fine wire twisted or braided together and it is very good for short and light aerials. Silicon bronze wire is stronger than copper wire and should be used where aerials are more than 100 feet long, while phosphor bronze wire is the strongest aerial wire made and is used for high grade aerials by the commercial companies and the Government for their high-power stations.

The spreaders should be made of spruce, and should be 4 feet 10 inches long for a three-wire aerial and 7 feet 1 inch long for a four-wire aerial as the distance between the wires should be about 27 inches. The end spreaders can be turned cylindrically but it makes a better looking job if they taper from the middle to the ends. They should be 2-1/4 inches in diameter at the middle and 1-3/4 inches at the ends. The middle spreader can be cylindrical and 2 inches in diameter. It must have holes bored through it at equidistant points for the hard rubber tubes; each of these should be 5/8 inch in diameter and have a hole 5/32 inch in diameter through it for the aerial wire. The leading-in spreader is also made of spruce and is 1-1/2 inches square and 26 inches long. Bore three or four 5/8-inch holes at equidistant points through this spreader and insert hard rubber tubes in them as with the middle spreader.

Assembling the Aerial.--Begin by measuring off the length of each wire to be used and see to it that all of them are of exactly the same length. Now push the hard rubber insulators through the holes in the middle spreader and thread the wires through the holes in the insulators as shown at A in Fig 9.

Next twist the ends of each wire to the rings of the ball insulators and then put the large withes on the middle of each of the end spreaders; fix the other withes on the spreaders so that they will be 27 inches apart and fasten the ball insulators to the eyes in the withes with the S-hooks. Now slip a thimble through the eye of one of the long strain insulators, thread a length of stranded steel wire 1/4 inch in diameter through it and fasten the ends of it to the eyes in the withes on the ends of the spreaders.(A) Fig. 9.--Middle Spreader. (B) Fig. 9.--One End of Aerial Complete. (C) Fig. 9.--Leading in Spreader.

Finally fasten a 40-inch length of steel stranded wire to each of the eyes of the withes on the middle of each of the spreaders, loop the other end over the thimble and then wrap the end around the wires that are fixed to the ends of the spreaders. One end of the aerial is shown complete at B in Fig. 9, and from this you can see exactly how it is assembled. Now cut off three or four pieces of wire 15 or 20 feet long and twist and solder each one to one of the aerial wires; then slip them through the hard rubber tubes in the leading-in spreader, bring their free ends together as at C and twist and solder them to a length of wire long enough to reach to your lightning switch or instruments.

Making a Good Ground.--Where you have to make a ground you can do so either by (1) burying sheets of zinc or copper in the moist earth; (2) burying a number of wires in the moist earth, or (3) using a counterpoise. To make a ground of the first kind take half a dozen large sheets of copper or zinc, cut them into strips a foot wide, solder them all together with other strips and bury them deeply in the ground.

It is easier to make a wire ground, say of as many or more wires as you have in your aerial and connect them together with cross wires. To put such a ground in the earth you will have to use a plow to make the furrows deep enough to insure them always being moist. In the counterpoise ground you make up a system of wires exactly like your aerial, that is, you insulate them just as carefully; then you support them so that they will be as close to the ground as possible and yet not touch it or anything else. This and the other two grounds just described should be placed directly under the aerial wire if the best results are to be had. In using a counterpoise you must bring the wire from it up to and through another leading-in insulator to your instruments.