RADIOACTIVITIES Newsletter of the Argonne Amateur Radio Club
Volume XLV, Number 7	September, 2004

02		AA9N		Clarence		Yorkville, IL
06		KV9Y		Ed		Burr Ridge, IL
07		NF9N		David		Orland Park, IL
10		N9HOH		Harold		Minooka, IL
12		N9FPQ		Raymond		Lemont, IL
13		N9TJW		Larry		Worth, IL
15		KB9CTJ		Loren		Minooka, IL
18		N9WQI		Jim		Paletine, IL
25		KA9WLT		Doug		Broadview, IL
26		K9CZB		Gary		Dixon, IL

How about this, ¼ wave on 40 meters is about 32’ and this works out to be ¾ waves on fifteen meters fed with a multiple of ½ wave feed line. I will say here that verticals incur losses at voltage maximums when an end is near a large tree. Move the top of the vertical at least six feet away. The impedance may be affected as well as the resonant frequency. The impedance changes from 35 to 75 or 80 ohms. Keep that in mind next field day.

I have recently put up an inverted vee beam with ¾ wave for each leg; that’s 99’ 7” long for 40 meters. Its SWR is flat, one to one, across the whole band. I have had just a few QSO’s on SSB and conditions seem poor. I have gotten 20db over S9 reports twice; Indianapolis, Indiana and Minnesota. I also worked a mobile in Missouri with the same report; these were daytime contacts.

The beam favors north and south. The antenna loads up on 80 meters too, but the noise is pretty high as is 40 meters, S5. I’m by high voltage power lines. It may load up on 15 meters, but I already have a beam on 15 and to close together to give it a try. The antenna is over 2 wave lengths long each leg, so there must be 4 to 6 db gain here. I haven’t tried loading it on 160 yet.

Speaking of 160, I remember W9NHM, Howard T. Francis, of Park Forest who passed away in 2003, and the long ago meeting at Evergreen Park field house off 95th St. presented by the Chiburbin Mobilers like in the 60s. Howard presented the “T” antenna for 160 meters to us. I have the paper from that meeting. I think it will be of interest for the newcomers and old timers. The diagrams cannot be duplicated here, but explained as best as possible. At that meeting he pointed out that a ½ wave on 160 meters still is 260’ and that the RF voltage and RF current in a resonant antenna are distributed in exactly opposite ways.

The voltage is always zero in the center and oscillates between high negative and positive values at each end of the wire. The current is always zero at the ends and oscillates between high negative and positive values in the center. Now, with the ¼ wave vertical called Marconi, the voltage at the ground is zero and maximum at the top and the current is maximum at the ground and zero at the top. This is not good since the radiation of a signal is better the higher the current at the top. A serious problem occurs when the maximum current is right at the feed point with earth and is wasted in heat by high resistant ground. We correct this with lots of radial wires under, branching out from the vertical. This aerial works but isn’t effective enough for us. We want more current at the top. We use short height antennas like 50’ because 130’ high is out of the question. We can put a coil at the base and many do. It is the easiest to do rather than putting it in the center or at the top. This coil has constant current, which makes the coil heat up causing heat loss. Why not use a capacity hat at the top?

Enter the folded top antenna. It is what Howard used at his QTH. The wire used is nearly 3/8-wave length rather than ¼-wave length. In this case, current is such that the maximum is located at the top of the vertical section, exactly where it should be. No loading coil at all or lossy ground connection and essentially all vertical radiation with little horizontal radiation. We get easy tuning over the entire band.

The antenna now looks like a “T” with the vertical portion 50’ to the top, a ninety degree bend going left 33’, a bend ninety degrees up one foot, then a ninety degree bend to reverse wire travel to the right 66’, then a ninety degree bend down for one foot, another ninety degree bend turning the wire to the left 33’ with the end of the wire to be secured and not soldered to the vertical 50’ portion.

We have a 160 3/8 wave length wire antenna and, because the horizontal currents in the folded sections are in opposite directions in adjacent wires, cancellation of fields occur, leading to greatly reduced horizontal radiation; thus, making most all of the energy go into the vertically polarized radiation. This antenna is not self-resonant on 160 meters when grounded. It must be electrically shortened by a quantity of capacitance in series with the wire and a fixed 300pf in parallel with a variable 250pf, with wide spacing to prevent arcing, then tied to a coil form four inches in diameter. Wrap 10 turns of number 12 wire; the bottom wire will be grounded. Wrap tape one layer over the 10 turns on the coil form. Now wrap four turns of the same type of wire on top of the 10 turns. Tie these ends and solder to coax either 50 or 75 ohm and run to transceiver. Install SWR bridge in line and tune the receiver to the frequency to use. Adjust the variable capacitor to peak the noise. Turn on the transmitter, monitor the SWR, and adjust the variable capacitor if needed.

1. To magnetize a steel bar: Put it into the ground pointed north and rap it with a hammer a few times. Remove with a car bumper jack.
2. Ground antennas: The deeper the antenna is buried, the more inefficient it is because earth absorbs the energy (skin effect). Example: A 20-meter dipole buried 4” deep has a feed point impedance of 456 ohms and radiates a vertically polarized ground wave. Thus a vertical buried dipole radiates a horizontal ground wave. Experimental lengths of dipole is 80% of its free space length. Lengths over 100’ not useful.
3. A counterpoise insulated above ground acts like a capacitor good to 1 wavelength with best results are on low frequencies.
4. Two antennas resonant; the one not excited will absorb 50% of the power.
5. Clean aluminum antennas by using Duro Aluminum Jelly or Burnside Aluminum Brightner.

1 mile E. of Manhattan	“Leave me alone”