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Ohms: 12K, 120K, 1.2M, 12M HIU/V dc mA: .05, 5, 50, 500 UillLl dB: 0, 14, 28, 34, 40

Whipping "Two' Mobile

The need for a better two-meter antenna for mobile use was the reason for trying both five-eighth and three-quarter whip base-toaded antennas. From the schematic, it will be noted that two antennas were tried out, one with a series coil, and the other with a grounded coil with a tap for impedance matching.

The parts required are:

1. Connector, of a type to be determined by individual need. However, in the grounded coil configuration, be sure to use a connector which makes a positive ground connection,

2. Plastic pill vial, size 1-1/8" 0,D. and 2-3/4" long, which can be purchased at your local drug stores' #14 enamel wire

4. 3/8" dia. brass rod stock, 2" in length

5. 2 ounces of casting resin, catalyst (4 drops per ounce) and coloring if desired. Dye will give a transparent effect, pigment opaque. These items can be obtained from most hobby shops.

6, 1/8" diameter metal rod, 53" long, for series coil antenna.

7, 1/8" diameter metal rod, 48** long, for ground coil antenna (these rods are much longer than necessary).

Alton E. GlazierP K6ZFV 3154 Jordan Road Oak Jan d, California 94602

Construction

Take the 3/8" diameter brass rod. From one end, drill a 1/8" diameter hole 1V4" deep. Measure 3/8" from this end, and at right angles to the previous hole, drill and tap for a 6/32" bolt. Measuring from the same end i", drill and tap for a second 6/32" bolt. On the opposite end of the brass rod, drill a hole deep, just large enough for #14 diameter wire.

The series coil is wound on a lA" diameter form, using #14 wire, 11 turns. The coil length is \Vi\ At one end of the coil, bend the #14 wire at a right angle, then clip off at 3/8". At the opposite end, bend #14 wire to a right angle, and clip at a distance of Scrape enamel off both ends. Solder the short end to the brass rod. Take the pill vial, and starting with a small drill, drill a hole in the center of the bottom. Slowly increase this diameter to 3/8", being careful not to crack the plastic.

Insert the brass rod with the coii attached into the open end of the pill vial and slip it through the 3/8" hole so the rod will protrude from the bottom of the vial for a distance of 1-3/8", Slip the coaxial fitting over the long end of the wire, and insert enough of the fittings so that it will be into the vial,

52 ohms

SERIES coil

Fig. 1, Coil encapsulated rn plastic pill vial.

5/8 X WHIP

52 ohms grounded coil

Three quarter wave whip with series but be sure the connector will be clear to operate.

Now center the brass rod and keep it parallel with the plastic container and the coaxial fitting. Solder the long wire to the coaxial connector. Check once again to be sure the fitting, the plastic vial and brass rod are all vertically in line.

In order to keep the plastic from escaping, and to keep the brass rod in line, it may be helpful to use either putty or a fast-drying glue. With the vial upright (coaxial connector up) you are now ready to pour the casting resin. This container will require two ounces of casting resin and eight to ten drops of catalyst. If coloring is desired, mix eit ler pigmented color or dye with the resin before adding the catalyst. See the manufacturers instructions for details on mixing, Carefully pour the resin into the vial, and let it stand for twenty-four hours.

The second antenna is made in very much the same manner, except the coil is wound on a 5/8" form. The total number of turns is six, and the spacing between turns is the width of the wire. The end opposite the brass rod is soldered to the outside material of the coaxial fitting, A piece of flexible #16 wire is brought up through the connector and is tapped to the coil two turns from the grounded end.

To prune t>»ese antennas to frequency, use a piece of expendable wire the same diameter as the fi^dl whip. Insert into the opening of the brass rod and secure with 6/32" bolts. Insert a standing wave bridge in the coaxial line, tune up the transmitter, and check the swr, which should be fairly high. Shut off transmitter and clip approximately W from the top end of the antenna. Turn on transmitter, retune, and check swr. Keep using this procedure until swr is at mini-

thepermaflexkey,

• both a twin lever Cr straight hand b*y in a pivaHess 2 paddle design,

• gives ¡nitant choice of automatic semiautomatic ¿r straight hand keying.

• use directly with any transmitter or through an electronic keyer.

• 8 amp. gold diffused stiver contacts adjust from 0-.060n (r 5-50 sramt.

• distinctive blue paddle* are of rugged G-IQ fiberglass epotty* 4 cabinet is 16 gauge polished chrome steeli 1.95' iq- paddles extend 1,25 weight app, I pound.

• silicone rubber feet for stability.

• JOCK US made Or guaranteed for I yr.

James Research compan 11 schermerhorn st^brooi completer ppd um & can. lend o check or m.o, told by mo LI only

Fig. 3. Five eighths wave whip with grounded coil.

mum. After finding the proper length, remove the whip and use this measurement for the permanent antenna, which will be made of spring rnetaL For best results, be sure this pruning procedure is done at the permanent position of the antenna on the vehicle.

The tests were conducted over as flat a terrain as possible, trying to preclude the possibility of reflections. Three different test sites were used. The reference antenna was a quarter-wave 19" whip. All tests conducted showed the long antennas to give better signal strength and less mobile flutter both on transmit and receive.

It would appear that possibly the three-quarter wave antenna has a higher angle of radiation than the five-eighths wave antenna; however, not a sufficient number of tests were made for angle of radiation to be conclusive. It would also appear that there was no advantage in one method of coupling over another. The number of tests made was thirty. Although S-meter readings in most receivers are rather meaningless, they do give us a relative indication as to strength. The thirty tests made showed an average increase of over one S-unit, The standing wave ratio of the various antennas was as follows: Quarter-wave, 1.3 to 1 Five-eighths wave, 1.1 to 1 Three-quarter wave length, 1.2 to 1

The antenna was located on the roof of a station wagon. The transceiver was an SR-42, and the standing wave bridges were a Mars and a Calrad.

Although it is never a good idea to encapsulate the antenna coil, in this case the inductance was so small that no apparent differences were noted between this type of construction and air-wound coils. It was apparent the mechanical advantages were well worth any slight degrading,

plastic pill vial i 1/0"XZ 3/4"

connector of choice plastic pill vial i 1/0"XZ 3/4"

connector of choice

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Communications AppJications Care of Fairchild Semiconductor 313 Fairchild Drive Mountain View, California 94041

Communications AppJications Care of Fairchild Semiconductor 313 Fairchild Drive Mountain View, California 94041

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