Antenna Support Mast

and Vertical Radiator

This unique design results in a sturdy, easily handled and effective support for a horizontal wire antenna as well as 'doubling' as a vertical radiator. Weight is less than 35 pounds and the cost is under

Howard S. Pyle W70E 3434—74+h Ave., S.E., Mercer Island, Wash.

Wire Antenna Support

\/fORE substantia and less costly construction of both vertical and horizontal wire antennas should prove a welcome addition to amateur radio design practice. Presented here is an innovation in the way of a combination antenna support mast for wire antennas which can serve as well as a vertical radiator for those who desire to experiment with both antenna types. Better still, it is so light in weight that it can easily be erected by two men, one holding down the base while the other 'walks it up\ If more help is available, put a man on each of two of the center guy wires for added insurance against bowing and swaying during erection.

Parts List

A—2" galvanized iron pipe cap

B—Pulley block of your choice

C—Down-haul rope or cable —about 35 feet required D- Shackle or auto tire chain repair Jink

Galvanized eye - bolt, U" x 3" with nut (insulated eye type) F—#8 x %" galvanized sheet metal screws (42 required) G—Wood reinforcing plug,

2" diameter by 18" tniip (4 required) H—P orcelain insulated screw eyes—t6 required) i——14 solid galvanized iron wire J—2r' diameter galvanized iron rain pipe <4 ten foot lenglhs required) K—2" #12 brass or galvanized iron round-head wood screw (Unless otherwise specified, only 1 each of above items required.)

While some difference of opinion exists among various authorities as to the proper height of a vertical radiator for amateur usage, popular pratiee seems to favor 33 feet, plus or minus a foot or so, depending upon the desired resonant frequency of operation, calculated from existing formulas. Such a height is the equivalent of a quarter wave-length in the 40 meter band, a half-wave on 20 and full wave on 10 and works well on all. On 15 meters, the efficiency is but slightly impaired and is really a matter of no concern. In the 75/80 meter band, functioning as a vertical radiator, the mast is somewhat less effective than at higher frequencies, but as the 75/80 meter hand is not considered a 'DX' band, the excellent ground wave propagation of a vertical of this height assures reliable communication over several hundred and often a thousand or more miles, dependent upon transmitter power. We have therefore settled on the mechanically practical height of between 32 and 34 feet which, in addition to being very effective as a vertical radiator, also permits a horizontal wire antenna to be installed at a satisfactory height above ground level, if desired.

The mechanical structure itself is somewhat unique in that instead of using a wooden mast or pole, with copper tubing down the side and topped with a 'whip' antenna, or using water pipe, electrical conduit or irrigation piping, rain-pipe of the 2" galvanized, round type is used. This is available from hardware stores, builders supply houses and plumbing dealers practically anywhere and at nominal cost. In the writer's area, it is priced at 15c per foot and comes in ten foot standard lengths. This means that you will need four of the ten foot sections and must necessarily discard a portion of one if your mast will 'double7 as a vertical radiator and is cut to resonance, The few feet you discard however, represent a very small loss which can be disregarded in view of the low over-all cost of the complete mast.

Mast Assembly

As supplied, pipe sections are fluted at one end for a few inches to permit telescoping. Cut off the fluted end with a hack-saw or tin

Parts List

A -2" diameter galvanize*! iron rain pipe (4 ten foot iengfhs required) B—Balsa wood spacer strips

(see text) C—10-24 Galvanized or brass stove bolt, 3" Ionr D—Wooden cross-arm insulator pin (see text) E— Solder lue to fit "C"

and "H" F—Galvanize*! split Jock washer to fit "C" C Galvanized or brass

10-24 nut H—Co-axial cable (RGS/U or RG58/U) (length as requiredJ I—Braid from co-axial ca-bie to ground clamp on

J"

J -Five or six foot; copper-

clad steel ground rod K—Mastic or roofing pitch waterproofing (see text > L—Petticoat type of pole line insulator {see text) M—x # 10 pan-headed sheet metal screws (2 re~ quired)

(Where no quantities specified, one only of item listed, required,)

snips. Procure from your local lumber yard, a six foot length of what is known as "full-round,J wooden stock in the 2" size. Cut it into four 18" lengths. These will serve as 'plugs' or connectors between sections and are shown at ug" in Fig. 1, and as "A" in Fig. 3. Use these to connect the sections* driving about half of their length into each end of the rain pipe and securing them with sheet metal screws as shown in the drawings. Butt the ends of the metal pipe closely together and run a generous solder bead completely around the metal joint for electrical contact between mast sections. Do not depend on this however; mechancially, the wooden insert will be adequate. Electrically, a litle wind sway in the mast could conceivably break the solder seal and destroy the electrical conductivity. So, make sure of this by strapping the sections together with galvanized plumbers tape or ground straps of copper at all three points (120 degrees apart) as shown at "D5t in Fig. 3, This *tape* or strap metal is generally sold in ten foot coils and one roll of ten feet will be sufficient for all joints. Use sheet metal screws as in Fig. 3 to hold it in place and then make it a good electrical joint by flowing a solder bead around it as in "E" of Fig, 3. Not only will these straps insure good electrical conductivity for your rf, but the mechanical strength of the joint will be greatly enhanced as well.

Your next step will be to saw, or cut with tin snips, the excess length of the initial 40 feet of mast assembly. Determine the length of the mast from handbook formulas and cut the top section to bring the over-all length into

conformity with your calculations. Remember to measure from the point of feeder connection at the base ("C,f in Fig, 2) to what will be the top of the mast.

Insert the final plug into the top of the mast and drive it flush, securing with sheet metal screws as shown at "F,f in Fig. t To prevent rain drip from going down the interior of the mast and rotting the wooden plugs cap the top either with a 2" galvanized pipe cap {"AM in Fig, 1) or a coffee can lid and a wooden, rubber or plastic ball, if you want to be really decorative. Toilet tank float balls, either plastic or metal will serve well here if you don't care for the fiat treatment of a pipe cap-

Mast Hardware

Your assembly of the mast itself is now complete, We assume that you have, of course, paid proper attention to supporting it on saw horses or boxes so that it assumes a perfectly level formation which will insure a plumb and pleasing appearance when erected. A sixteen or twenty foot length of x 1%" lattice (real cheap at lumber yards) makes a good straight edge, when used edgewise, to check this. Your next step is installation of a few hardware items on the mast. First, let's mount the guy wire anchors. If this were to serve only as a supporting mast for a horizontal wire antenna we could gel by here with conventional galvanized iron screw eyes or eye-bolts. However, as we might want to use this also as a vertical radiator, either initially, or later, why not make provision for such use now? So, let's use the ins-u fitted type of screw eye, commonly

available in all TV and radio stores for a few cents. By so doing you don't have small radials and poor rf contacts to upset your theoretical calculations for antenna height vs. frequency. And you'll find it a big help in avoiding TVI which could result from microphonic contact between guy wires and mast!

OK; mount three of these insulated screw-eyes about 16" down from the top of your mast, spaced 120 degrees around the circumference. They will serve as anchors for your upper series of guy wires (see "H" in Fig, 1). Do thti same at either the ten or twenty foot level of the mast; they will anchor your second set of guys, I prefer the twenty foot level but do as you see fit. You can even drive an additional wooden plug half-way into the second (from bottom > section of the mast if you want the lower guys at a point about half-way up; the decision is yours. Remember to 'stagger' the screw-eyes at least half an inch in the vertical plane or their shanks will collide!

And now, the final hardware mount; the eye-bolt at the top of the mast (a few inches below) which will receive the pulley block for the down-haul for the wire antenna. This eye-bolt should also be insulated and can be a galvanized type, t'lree inches long, going clear through the mast and wooden plug as shown in Fig. 1 at The pulley block itself can be anything you choose; galvanized iron, bronze, Wood block with metal sheave, etc. Connect the eye of it to the eye-bolt in the mast with a conventional 'shackle' (hardware stores or marine supply houses) or, if no local source for shackles, use an automobile tire chain repair link, available at any automotive service station, tire shop or auto supply store.

Now, if you have your guy wires in place and your down-haul riven through the pulley sheave, you need only cut the guy wires every fifteen feet and insert a suitable insulator. This should preferably be of the compression type as, in the event of breakage, the guy does not let go. The small, glazed porcelain type known as 'airplane' strain insulators, are ideal; these sell for less than 10c each at most radio stores. With their installation, work on the mast itself is now complete, mechanically. We recommend that you now give it at least two thorough coats of a lead base paint in any color that suits your fancy. Not only will this act as a preservative against rust, but will considerably improve the appearance of your final mast.

Parts List

A—2"xl8" length of *fulU round' wooden pole 14 required) B—2" diameter Kfilvanized iron rain-pipe (4 ten foot lengths required) C—s #8 pan-head gal-vanixed sheet metal screws (i2 at each joint)

D—Perforated steel strap— about ten feet required (see test) E—Solder application (see text)

Mast Base Mounting

While the paint on the mast is drying (two coats take several days you know) it's a good time to prepare the base mounting. This Isn't too bad and involves only digging a hole in the ground about a foot square and approximately ten inches deep. Make a little form of scrap lumber if you're meticulous, let it protrude about two inches above the ground level. Pill the thing with concrete; you can get "ready-mix1' sand, gravel and cement in a convenient bag at your lumber yard). Follow the consistency instructions on the sack and you'll come out all right. After it sets up about half hard, bevel the top four edges if you like for a more professional job. At the same time, scoop a circular depression in the center of the top of the concrete base to act as a 'socket' for the base insulator to !>e next described. Use a trowel for this operation or you can use the insulator itself in 'pestal* fashion to achieve this. Now you can leave the base alone while it sets up (about 24 hours). The base insulator should next be procured and mounted on the mast. See the 'outside line construction foreman' of your local power or telephone company and show him Fig* 2. He will immediately recognize and "D" as a standard cross-arm insulator ("L") and wooden mounting pin ("D"), Wheedle, cajole or buy such a combination from him ... it will cost you little. The insulator can be either glazed porcelain or of blue/green f>otl5e glass as used by the phone companies. Either is more than adequate electrically and mechanically.

The end of the wooden pin opposite the threads will be too small for your 2" mast Build it up to the 2" diameter required with short wood strips (4), nailed with small brads to the pin itself. Balsa wood, usually available at most lumber yards, variety stores and hobby shops, will work well here. Get something about half an inch wide and of a suitable thickness to fill the gap when installed as shown in Fig. 2 at "B". A foot of this stock will be adequate. Mount the insulator and it's pin as in Fig. 3 and you've got a complete antenna mast and vertical antenna ready for erection when the paint dries!

Your ( ompletcd Antenna Support Mast/Vertical Radiator

Should Look Like This!

A—Horizontal wire antenna B—Insulator for "A" C—Down-haul rope or cable (use a sash weight at lower end or anchor to a cleat or eye-bolt near base of mast) D—Guy wire (#14 galvanised iron) E—Airplane type of 'Voose-

egp" strain insulator F—Glazed porcelain or *bott le-E lass* petticoat pole * line cross - arm insulator

G—Concrete base; about 1

cubic foot H—Co-axial cable feeder i RGS/U or RG5S/U) I—Ground rod (5 or 6 foot, copper clad steel with clump)

.1—Porcelain insulated screw-eye insulator K—fruy wire anchor

Again you don't have much of a problem in tying your guy wires into the ground. You'll need first three spots 120 degrees apart (approximately) and at a minimum of IV2 feet from the center of the mast base. 10 feet is better, but will do very well. With a piece of string, centered on the mast base, you can scribe a circle on the ground and determine your anchor points. Maybe you have a convenient tree, a stump or a building which will serve, in the approximate area, If so, use it. If not, you have several choices for guy anchors. You can buy conventional, drive-in or screw-in types of pole line anchors from your power company; they won't be cheap however, You can dig a hole about two feet deep and three feet square, make a cross of a couple of 30" 2" x 4" timbers and lay them in after wrapping some stub lengths of guy wire around them to which you can tie your guy wires above ground. Or, you can dig holes about a foot square and 18" deep, set a six or 8 inch eyebolt (galvanized of course) in the approximate center, pour the hole full of concrete mix and wait for it to set. Any of these methods are good; you choose the one which you like best Even six foot lengths of 1" pipe, driven at about a 30 degree angle, will do the trick.

And, with all of the above done, you need merely raise your mast, tie on the feed-line as shown in Fig, 2, or raise your wire antenna in place, or both, and you're "on the air" with either a wire antenna or a vertical or both at will, as you choose! Lay back now and take it easy; this is a mast which will last you a 1-o-n-g 1-o-n-g time! ™

The Diligent Detector

73 Staff

So far as most of us are concerned, the 1 detector is the "forgotten man7 in a communications receiver. Ultra-simple circuitry, tried and true over the years, tends to make us think of the detector (when we bother to think about it at all) as one of the most nearly perfected parts of the set.

The general impression that detectors have little room for improvement isn't correct. For a few cents worth of parts and a few minutes time, you can reduce your set s detector distortion to a fraction of its previous value.

his will do a near-miraculous job of cleaning up formerly-muddy signals whose only actual fault was 100 percent modulation, and may even restore broken friendships if bad signal reports caused the breach!

You can take your choice of a number of circuits to accomplish this end, thanks to the audio fraternity which devotes much of its time to reduction of distortion* Some are nearly as simple as the conventional detector, while others involve addition of one or more tubes to the set.

Each of these circuits has its own set of advantages and disadvantages, making the choice a bit more complicated than one of mere time and complexity. The purpose of this article is to list these circuits, together with their pros and cons, to make it easy for you to pick the one best suited to your own needs.

Before going into the newer and more-sophisticated detector circuits, a brief review of the conventional detector is in order. To

Fig, This basic circuit, or slight variations of it, is the second-detector in use in nearly every radio receiver on the market today. Except for the filter, the circuit Is identical to a half-wave power supply but operates in a completely different fashion.

clarify the approach used in this review, you know that an ordinary AM signal may be visualized in either of two ways: It may be con* sidered to be a single, steady carrier wave varying in amplitude, or it may be thought of as an unvarying carrier accompanied by sidebands of varying strength which are later mixed with the carrier to produce sound.

While the second visualization is more correct in the mathematical and physical sense, there is no measurable difference between the two. To avoid complicating this article with exotic mathematics, the first (and older) visual ization has been used in explaining diode-detector action.

Since the most common detector in use today is the diode, ict's look at it first. Most diode detector circuits are similar to that shown in Fig. I, You may find a crystal diode instead of l!te tube in some receivers, but i \e principles of operation remain unchanged.

Similarity between this circuit and an ordinary half-wave power supply (less filter) is evident. However, the two circuits differ drastically in several important operational details.

In a power supply, the design factors are chosen so that current will flow over as much of the cycle as possible without flowing during the reverse half-cycle- This reduces ripple voltage in the output to a minimum.

In the detector, however, the objective is to make current flow through the diode in a series of extremely short pulses. This is accomplished by making the resistance of R1 very large compared to the diode's forward resistance, and by making the applied signal voltage as large as possible without running into overload.

Under these conditions, CI is charged by the short pulses, and if the time constant is properly chosen the capacitor voltage will rise almost to the peak value of the applied signal.

he voltage will vary in a linear manner with the strength of the applied signal as measured at the peak. For this reason the circuit is known to engineers as a "peak-linear" detector.

Note that the voltage impressed on CI will follow the signal modulation envelope only if the tube voltage drop is negligible compared to applied voltage. At low signal levels, every rectifier becomes a "square-law" device whose

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