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What's Your EQ?
April 1966 Radio-Electronics

April 1966 Radio-Electronics

April 1966 Radio-Electronics Cover - RF Cafe[Table of Contents]

Wax nostalgic about and learn from the history of early electronics. See articles from Radio-Electronics, published 1930-1988. All copyrights hereby acknowledged.

Two Currents Solution Kirt Blattenberger - RF CafeThese two circuit puzzlers appeared in the April 1966 issue of Radio-Electronics magazine. When working out the problems, I managed to interpret the goal in the "Two Currents" one. Despite the name, I instead solved for the two values of resistance, not the two currents. So as not to have wasted my effort, a photo of it is posted to the left. At the bottom of it, I multiplied my two resistances by the author's two currents and arrived at the stated 2 watts for each. QED. The "Rise Time" challenge is similar to one posted a short while ago. If you've used an oscilloscope to measure rise times, you are probably familiar with the phenomenon.

What's Your EQ?

What's Your EQ?, April 1966 Radio-Electronics - RF CafeTwo puzzlers for the student, theoretician and practical man. Simple? Double-check your answers before you say you've solved them. If you have an interesting or unusual puzzle (with an answer) send it to us. We will pay $10 for each one accepted. We're especially interested in service stinkers or engineering stumpers on actual electronic equipment. We get so many letters we can't answer individual ones, but we'll print the more interesting solutions - ones the original authors never thought of.

Write EQ Editor, Radio-Electronics, 154 West 14th Street, New York, N. Y. 10011.

Answers to this month's puzzles are on page 91.

Conducted by E. D. Clark

Two Currents - RF CafeTwo Currents

Rheostat R2 can be adjusted to two different values at which it will dissipate 2 watts. What are the two circuit currents?

- C. A. Kelly

 

Rise Time - RF CafeRise Time

A circuit is designed to produce a square wave with a rise time of 10 μsec. However, when the waveform is viewed on a scope (type with a changeable vertical preamplifier), the rise time appears longer than that.

After checking the setup, it is found that the long rise time is the fault of the scope. Why?

- Donald Ludwig

Quizzes from vintage electronics magazines such as Popular Electronics, Electronics-World, QST, Radio-Electronics, and Radio News were published over the years - some really simple and others not so simple. Robert P. Balin created most of the quizzes for Popular Electronics. This is a listing of all I have posted thus far.

RF Cafe Quizzes

Vintage Electronics Magazine Quizzes

Vintage Electronics Magazine Quizzes

Vintage Electronics Magazine Quizzes

Answers to What's Your Eq?

These are the answers. Puzzles are on page 60.

Two Currents

Combining Ohm's Law and a power formula, we get 50I2 + 2 = 251. This is a quadratic equation (ax2 + bx + c = 0) In this equation: a = 50, b = -25 and c = 2.

50I2 - 25I + 2 = 0

The general quadratic formula is:

x = (-b ± √b2 - 4 ac)/2a

Therefore, I = (25 ± √625 - 400) /100

I = (25 ± 15)/100

(25 + 15)/100 = 0.4  and  (25 - 15)/100 = 0.1 amp.

 

Rise Time

The rise time of the square wave is faster than the rise time of the scope. To find the Answer rise time of a scope, use the formula:           Square root - RF Cafe

In the formula, tr is the rise time of the display seen on the scope, ts is the rise time of the scope (usually given in the specs) and ta is the given rise time of the vertical preamplifier.

For example, if ts is 20 μsec and ta is 15 μsec, tr equals 25 μsec.

Square wave calculation - RF Cafe 
Rigol DHO1000 Oscilloscope - RF Cafe

About RF Cafe

Kirt Blattenberger - RF Cafe Webmaster

Copyright: 1996 - 2025
Webmaster: Kirt Blattenberger,
   BSEE - KB3UON - AMA92498

RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The World Wide Web (Internet) was largely an unknown entity at the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps while tying up your telephone line, and a lady's voice announced "You've Got Mail" when a new message arrived...

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