Among the Novice Hams
November 1957 Popular Electronics

November 1957 Popular Electronics Table of Contents Wax nostalgic about and learn from the history of early electronics. See articles from Popular Electronics, published October 1954 - April 1985. All copyrights are hereby acknowledged.

As with on my Airplane and Rockets hobby website, a big part of my motivation for scanning and posting these vintage electronics magazine articles has been two-fold. The first reason is to provide access to historical documents for educational reasons. The second reason is to have the names of people and places published in text format (everything OCRed) so that someone doing a Web search for himself, a relative, or a friend, might run across it here. I receive e-mails occasionally from readers who are thrilled to find those names in an old article.

Among the Novice Hams

By Herb S. Brier, W9EGQ

In October we discussed some of the fundamental properties of current, voltage, and resistance, and how the relationship between them is expressed concisely by Ohm's law: E = IR, I = E/R, R = E/I. We also talked about the formulas for calculating the power in electrical circuits, P = EI and P = I²R, and how to use them answering simple questions involving Ohm's law and power calculation that may found in the Novice examination. Now, we'll go over the information necessary to understand and answer questions that might appear in the General/Technician/Conditional exam.

Fred Beyer. KN9HFP, made 200 contacts in 35 states in five months as a Novice. His transmitter is a DX·20 feeding a dipole; His receiver is an NC-98.

In the General Class examination, there are usually a couple of questions based on the diagram in Fig. 1, such as: "What is thee bias voltage on the tube?" And: "What is the resistance of R2?" It is important to read each question separately and then study the diagram to determine which of the data given is pertinent to that question. Once this is done, the problem is half solved.

Fig. 1. This diagram, with different component values, is the basis for several questions on Ohm's law which appear in the General Class Amateur exam.

For example, there is nothing difficult about determining the resistance of R2. From Ohm's law, R = E/I; therefore, you simply divide the voltage across R2 by the current flowing through it. Both of these quantities are given. Remembering to change milliamperes to amperes, the solution will be:

Amateur radio is a hobby in which a quarter million people throughout the world, from grade school boys and girls to men and women, operate their own officially licensed radio stations. They communicate with each other over distances ranging from a few miles to 12,000 miles.

Ken Grimm, KN5KBH, works 16-meter c.w. with a DX-100 transmitter cranked down to 75 watts at Baylor University Radio Club.

The simplest amateur license to obtain is the novice license. It is issued by the Federal Communications Commission, Washington, D.C., to any citizen who has not previously held an amateur license and who can send and receive the International Morse code at a speed of five words a minute - actually a very slow speed. In addition, it is necessary to pass a simple written examination on elementary amateur radio theory and regulations. The license is valid for one year, during which time the licensee must qualify for a permanent license or leave the air.

Referring to Fig. 2(B), the first step in calculating the resistances in the voltage divider is to decide on how much "bleeder current" to allow to flow through it. Normally, about 10% of the current capacity of the power supply is allocated for the purpose. Ten percent of 200 ma. is 20 ma. When added to the 160 ma. drawn by the transmitter, this makes the total key-down current drain on the supply 180 ma.

Fig. 2. How resistances connected in series (A) can be used as a voltage divider (B) to deliver several voltages from a single power supply (see text).

Starting at the bottom of the divider, the only current that flows through R1 is the bleeder current, while the voltage across it is obviously 100 volts. Substituting these values in the appropriate Ohm's law formula gives:

Under no-load conditions, the voltage at the divider taps will be higher than when they are under load. The main advantage of a voltage divider over series dropping resistors is that voltage variation between the load and no-load conditions is minimized.

Resistances in Parallel. Figure 3 shows three resistances in parallel. The formula for calculating the effec-tive resistance of such a combination is:

If you are a whiz at algebra, you know exactly how to solve this formula and need not worry that you may be asked about it in the examination. If not, you will probably say: "Fine, but what does it mean?" Fortunately, it's easy to understand with a bit of explanation.

Fig. 3. How to calculate the effective resistance when three resistances are connected in parallel.

Referring to Fig. 3 and taking each resistance in turn, we know from Ohm's law that the currents through them are: I1 = E/R1, I2 = E/R2, and I3 = E/R3. Furthermore, the total current is the sum of the individual currents:

I_total = I1 + I2  + I3, or I_total = E/R1 + E/R2 + E/R3.

Reverting to the fundamental Ohm's law again, the effective resistance of the three resistances in parallel is:

Of course, we can make E any value we wish, as long as it is the same in each part of the equation. For convenience, E is usually made equal to one volt in parallel-resistance calculations, making the last equation the same as the first one given here.

The effective resistance of 2-, 4-, and 5- ohm resistors in parallel is 1.05 (to two decimal places). I suggest you verify this answer for practice and then make up a few practice problems of your own. In checking your answers, remember that the effective resistance is always less than that of any of the individual resistances.

Posted June 27, 2012