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What's Your EQ?
February 1966 Radio-Electronics

February 1966 Radio-Electronics

February 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.

If it seems like I've been posting a lot of these "What's Your EQ?" features, there's a good reason... I have been posting a lot of them lately. I had created the pages long ago, and somehow I forgot to go back and complete them with the drawings. Expect to see a dozen or so more in fairly short order. The circuit challenges are usually submitted by Radio-Electronics magazine's readers, but occasionally one of the columnists will contribute. "How Wide?" seems like you would need the value of L to calculate, but given that the problem is presented without it, there must be a way, right? With the Series-Parallel circuit, I got as far as the voltage at the junction of R2 and R4, but couldn't come up with enough equations for the given number of unknowns. Turns out, you have to make an educated guess until you get values that satisfy the requirements. Duh. Black Box problems stump me more often than I can to admit publically.

What's Your EQ?

What's Your EQ?, February 1966 Radio-Electronics - RF CafeConducted by E. D. Clark

Two 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 101.

How Wide the Bandwidth? - RF CafeHow Wide?

Find the bandwidth (M) of the tank circuit in the diagram.

- William Uhlenhoff

 

Series-Parallel Circuit - RF CafeSeries-Parallel Circuit

From the information given on this series-parallel circuit, can you determine the values of R4 and R5, also the current flow through R3, R4 and R5? Disregard the meters' internal resistance.

- Chester A. Kelley

 

 

Two Lamps - RF CafeTwo Lamps

Two lamps and a spst switch are mounted in this black box. With the switch in one position, one lamp is on. In the other position, the other lamp is on; both lamps are not on at the same time. Power is supplied to the box from a 115-volt 60-cycle source. No relays or transistors are involved.

What's the circuitry in the box?

- R. A. Reiss

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 61.

How Wide Bandwidth? (answer) - RF Cafe How Wide?

At first this appears impossible since no value is given for L. However, there is a solution.

(1) Δ = fr/Q where fr = 1/2π √LC and Q = R/XL = R/2π fr L

Substituting for Q in equation (1):

(2) Δ = f = fr/(R/2π frL = (2π fr2L)/R

Substituting for fr in equation (2):

Δf = ( (2π L/4π2 LC) )/R = 1/(2π RC)

Substituting given values of R and C:

Δf = 159 kc.

 

Series Parallel Circuit (answer) - RF CafeSeries Parallel Circuit

By determining the voltage at point A (55 volts), R1 can be eliminated. The remaining total resistance must be 1,250 ohms (55/0.044). If we make the value of R4 and the combination of R2, R3 and R5 both equal to 2,500 ohms, they equal 1,250 ohms when paralleled. To make the combination equal to 2,500 ohms, R5 must be 3,000 ohms. (3,000 paralleled with 3,000 equals 1,500. This in series with 1,000 equals 2,500.)

There is 0.022 amp current through R2 and R4. This current is divided equally (0.011 amp) between R3 and R5.

 

Two Lamps (nswer) - RF CafeTwo Lamps

With the switch open, current flows through Lamp 1 on negative half-cycles (Lamp 2 being shorted by D2); no current flows when the ac goes positive. With switch closed, Lamp 1 is shorted and current flows through Lamp 2 on positive half-cycles. When the ac is negative, the current is "bypassed" through D2.

The resistor prevents excessive current when D2 is directly across the supply.

 

Other Solutions (from July 1966 R-E)

Because of inadequate description of the "Two Lamps" puzzler (Feb. R-E) several readers offered alternate solutions. These consisted mostly of a neon (or low-wattage incandescent lamp) in series with a larger incandescent lamp.

In operation, with the switch (connected across the smaller lamp) open, there is negligible voltage drop across the larger lamp. This causes smaller lamp to light with near normal voltage. With switch closed, the larger lamp receives full voltage.

One solution used 40-volt lamps with a transformer-operated resistor-bridge circuit.
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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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