RADIOACTIVITIES Newsletter of the Argonne Amateur Radio Club
Volume XLVI, Number 1	January, 2005

04		KA9PVD		Paul		Downers Grove, IL
08		N9WJI		Raymond		Naperville, IL
09		W9VWS		Steve		Clarendon Hills, IL
12		N0GVY		Bill		Estes Park, CO
14		WA9ZPM		Mike		Crestwood, IL
21		KB9UJB		Bill		Downers Grove, IL
22		W9CLM		Chuck		Plainfield, IL
22		N9GF		Gus		Melrose Park, IL
27		KC9EUY		David		New Lenox, IL

Harry Mills, W4FD, and friend Gene Brizendine, W4ATE, in 1978 wrote an article about doing this. It maybe fuzzy logic theory all W4FD concept: The radiation from a capacitor directly is minor, but not eliminated because a device for the control of phasing. The capacitor pushes antenna current to all parts of the radiator and distributed in phase, so superior results occur the current equalize and eliminates the standing wave. The most important characteristic of a capacitor is its inherent low loss seeing it in the vital role of filtering out antenna current into efficient distribution pattern by equalizing current throughout the radiator by using numbers of capacitors. A standing wave radiator sends energy out varying angles worst toward the ends. Approaching equal current along the aerial, radiation focalizes at low angles. Good for DX when even close to ground.

Now comes W4FD U.S. Patent 3,564,551 granted Feb 1971. His scheme: a dipole element employs ferrite tunable over wide range of frequency by varying the permeability of sleeved cores. This material must be under conditions of high current and low voltage because of its high dielectric properties. So the control current scheme used cored sleeves over the entire radiator to extend the frequency tuning range. The problem was solved by cutting the antenna conductor into 22 or more even number sections of equal length, which are inter connected in alternate series 20 or more equally valued fixed capacitors.

The aerial always begins with wire sections at the center feed line point and ends with wire sections. The control current principal is the idea of top or end loading. It can be seen using the horizontal dipole with aluminum screen discs at the ends of ½ wave radiator into a series of alternate wire and capacitor sections might improve both current distribution and radiator gain. Maximum usage begins at the point where in phase equal current fills the capacitor. A 5/8 wave serial produces its peak gain at this length because an increasing out of phase component and its expanded aperture. Gain lowers at aerial length above and below the 5/8-wavelength figure. So to increase gain the capacitor lower in loss than an inductor coil could be used. Using the alternate wire capacitor as values of capacitors are increased and wire length section is decreased the RF wave ripple along the aerial will tend to smooth out. The capacitance loading discs serve to carry uniform current nearer the radiator end.

Some features where controlled current departs from the usual dipole. Select wire lengths desired and determine what capacity in Pico farads is necessary to partly cancel the inductive reactance of the wire sections. Too low capacity choice will create too high a capacitive reactance and therefore over cancel the inductive reactance of the wire sections. Too small a value will prevent resonance regardless of how many sections are added. The Xl to Xc ratio is the key to proper aerial performance.

The superior characteristic of controlled current system became apparent when the radiator overall length is extended one electrical wavelength and beyond. End loading discs can then be dismissed. The capacitor is passive as to the radiation process, but its low loss ability to current distribution and hence phasing gives it a unique place in aerial design. Another characteristic is immunity to the effects of close by nonresonant conductors. In one test W4FD laid the aerial flat on soaking wet ground in the rain and got S9 reports from Miami to Cincinnati; he being in Georgia on 40 meters.

The good points: greater gain, elimination of end effects, higher aerial resistance, full use of aerial element current - no nodes, lower radiation angle, no high voltage points, works well 8 feet up, no phasing stub, broad banded, & good harmonic aerial. Harmonic operation becomes more effective as the number of capacitive units is increased and conductor sections are proportionally shortened. Rule of thumb: for a given overall antenna length, shortening the wire sections by ½ doubles both the number and the capacitance values of the fixed capacitors required. Broadside pattern is improved at both fundamental and harmonic frequencies with an increasing number of sections. Aerial drawback: costs of wire, capacitors, insulators, time, more care in construction and testing, more land needed for erection, and on 80 meters shunting resistors needed for static charge.

Forty meter DX tests Xmit and receive favor current control aerial by 5 to 7 db over a reference dipole. Making one of these aerials, use nylon rope to tape the capacitors and resistors onto it. Resistors are 1 watt 20 to 50k ohms across each capacitor. Resistor acts like a choke against static charges and lightning. The type of capacitors are polystyrene, silver mica, or mica 5% tolerance in that order, voltage 200dc working.

A mathematical equation establishes which series capacitors can be used to a certain K value for each band. Example: You have 26 five-foot wire sections with 24 capacitors in the aerial and find 270pf per capacitor is proper for resonance at 7MHz. Then, K=270 / 24 = 11.25, the effective series capacity of the string.

We can use this K figure for calculating closely what capacitor value to use for other bands and with other wire section lengths and capacitor values. The K value for 3.5MHz would be around 22. If capacitors in Table One are available, use them. It’s only necessary to adjust section wire lengths and numbers proportionately. Example: you have 470pf capacitors on hand, an aerial at 7MHz desired. Find the even number of wire sections required; 470pf / 8.48 (K for 7MHz) = 56 wire sections. From Table one, the overall length is 140 feet or 1680 inches (140 * 12). Now, find the wire length; 1680 / 56 = 30 inches and the number of capacitors is always 2 less than the number of wire sections or 54 here.

Details: Test every capacitor value to be within 5% or the aerial will fail to operate even with a single defective capacitor. Every aerial must be resonated by adding or subtracting complete sections while the frequency is monitored with an accurate dip meter. An equal number of sections must be added or removed at each of the radiators in order to keep system balance. If that resonance occurs at the low frequency end of the operating band, this will improve high frequency harmonic operation. During adjustment, suspend the aerial 5 to 6 feet from earth. Put temporary coil across the feed point for dip meter coupling (use 8 turns or less for best measuring accuracy). To enable the builder to reach the desired frequency antenna length, frequent measurement of higher harmonic resonances will be helpful with optimum performance occurs at length where addition of more sections produces little or no changes in resonant frequency. Finer adjustment must be made while watching the dip meter reading at the fundamental frequency. Note: short sections ten inches W4FD and 5 ¾ inches at W4ATE promise improved aerial for under water submarine communications.

W4FD wrote another article that appeared in the July ’81 73 Magazine with helper W4ATE. A professor, W8VWX, at Ohio State University marveled about his “CC” aerial saying he could work very weak DX and is usually 5th to 10th in pileups for a contest.

Can any capacitor be used? It is best to adjust wire lengths and number of sections from Table One. You have 100 470pf capacitors on hand for 7MHz. Find K: 470pf / 8.48 = 56 wire sections. Then, from Table One, 140 feet is 1680 inches. Find the length of each wire section: 1680 / 56 = 30 inches. The number of capacitors is always 2 less than the number of wire sections; thus 54 here. There is no set number of capacitors required, but more is better for current distribution. In general, 40 to 60 will do the job. The best broadside gain is when all equal capacitors are connected in series with wire sections, the RF voltage across each is typically 80 volts, even with one KW input from the final amplifier. Such capacity must be within 5% of value of capacitance. Above 470pf, they should be polystyrene, silver mica, mica, dipped mylar, or any low loss type. This antenna is a good performer inside an attic or building even when strung through trees or shrubbery and at low heights or lying on the ground. The radiation resistance varies little when end loading capacity discs are added it has wide bandwidth above its resonant frequency. Impedance at the center is close to 250 ohms; it can be fed with open 45-ohm line. To check the antenna, use low power and a neon fluorescent lamp, & dip meter in diode mode. If a point is reached walking along its length where no indication is found, the last capacitor passed over may be defective. If RF is lost at both ends at about equal distance from feed point, then wire sections may be shorter or capacitors larger in value by the formula.

Trying to operate below resonant frequency, the aerial acts like a high pass filter. Some people who have built these prior to July 1981 are K2GGD, W2IMU, W2SVI, W4DNX, W4KIX, W4OQT, W4KXC, W8VWX, WD4DSX, AC5P, K8AA, AA6US, WB8RGN, & KK4X.

Calculate with reasonable accuracy design parameters fro any frequency. Formula (2): S - 2 = Fc / 59.35, where 59.35 is a constant, S - 2 equals the number of capacitors and S equals the number of wire sections, & Fc = resonant frequency in MHz. Formula (3): Lt = 984 / F * 12, where Lt equals total length in inches for one wavelength, F = the resonant frequency in MHz, & 984 is a full wave constant. Formula (4): Ls = Lt / S, where Ls = the length of sections in inches, S = number of wire sections from Formula (1), & Lt = the total length in inches for one wavelength.

What is the aerial dimensions for 7MHz with 150 feet of wire and a batch of 390pf mica capacitors? First, check each capacitor for 5% tolerance of 390pf. Apply Formula (2): S - 2 = 7MHz * 390pf / 59.5 = 46 capacitors, then S = 46 + 2 = 48 wire sections. Apply Formula (3): Lt = 948 / 7MHz * 12 = 1686.85 inches overall length. Apply Formula (4): Ls = 1686.85 / 48 = 35.14 inches length of each wire section. To sum: 46 capacitors of 390pf, 48 wire sections each 35 inches long, & a total aerial length of 1686.8 inches or 140.57 feet.

It is interesting to note off end radiation increases in to equal the broadside value when elevated 1/8 wave.

Another Control Current article appeared in the May 1982 issue of 73 Magazine by W4ANL. He built his aerial for forty meters, used no balun, but open 300 ohm feed line and tuned the aerial via a matchbox and says his is the best single wire aerial ever built.

He tuned his 80 meters and was able to put out a signal good for local work. He used 140 feet of #22 wire from the secondary of an old power transformer. He used 46 one watt 47k ohm resistors, 46 malbry capacitors of 390pf at 160 volts dc. He tested the capacitors and found 2 bad ones that were over 5% tolerance. He checked it out after construction using a three turn loop across the feed point, used a grid dip meter and found 7002MHz as the resonant frequency. The use of a tuner permits the residual reactance to be varied out. Using low power next made a RF indicator by using a 50ua meter and a couple of 1N34’s as rectifiers and a 6-inch wire was used as a RF probe. Holding the probe and walking along the aerial measured each section. At the end section he had 12ua near the middle of the wire sections and he had 29ua and it was so for the other sections.

No DX contacts were mentioned, but, then, not everyone is a DXer.