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Kirt Blattenberger (KB3UON)

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Bridge Function Quiz
September 1969 Popular Electronics

September 1969 Popular Electronics

Popular Electronics Cover, September 1969 - RF CafeTable 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.

Quartz crystal bridges, half-bridges, Wien bridges, Schering bridges, Maxwell bridges, full bridges, Wheatstone bridges, shunt bridges. Who knew there were so many different types of bridge circuits? If you can ace this Bridge Function Quiz, then you are truly an analog circuits guru. It appeared in the September 1969 issue of Popular Electronics magazine, and is one of Robert Balin's most challenging quizzes. I can think of maybe four or five people I have known over the years who are likely to be able to correctly answer all ten, and no, I am not among the revered few. In the days of yore when electronics repair shops were ubiquitous across the land, there were many Mac McGregor types, of Mac's Radio Service Shop fame, who could easily perform such a miracle. Such circuits were common in radio and television sets back then.

Bridge Function Quiz

Bridge Function Quiz, July 1969 Popular Electronics - RF CafeBy Robert P. Balin

Many electronic components-vacuum tubes, transistors, diodes, thermistors, etc. - are often connected in the form of a bridge, which can make a particular circuit more sensitive and efficient. With the bridge balanced, one gets a zero-current-consuming indication of relationships between components in the circuit. To test your knowledge of bridge circuits, match the functions (1-10) to the proper diagrams (A-J).


See answers below.

Quizzes from vintage electronics magazines such as Popular Electronics, Electronics-World, QST, 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


Electronics Bridge Function Quiz Answers

1-E)  A half-bridge amplifier circuit is used in vacuum-tube voltmeters to provide high sensitivity and high input impedance. A "zero set" potentiometer balances no-signal tube currents.

2-D)  This quartz-crystal full bridge is a bandpass filter employed in SSB transmitters to obtain the narrow bandwidth required. Within the passband, the impedances of the two pairs of crystals, 1-4 and 2-3, differ widely due to their different resonant frequencies, thus causing the bridge to be unbalanced and permit a large signal output.

3-B)  A Wien-bridge band-suppression filter employs series and parallel RC circuits to keep the bridge unbalanced outside the rejection band. Within the band, the impedances of the RC circuits change in opposite directions to balance the bridge and attenuate the output.

4-G)  This capacitance measurement circuit is a Schering bridge using standard capacitors to determine the unknown capacitance. Capacitor C1 balances out the resistance of the unknown while C2 is calibrated to indicate the unknown capacitance when the bridge is balanced.

5-C)  A Wien-bridge frequency measurement circuit employs two calibrated potentiometers, R1 and R2, varied simultaneously in equal increments to indicate the unknown frequency when the bridge is balanced.

6-A)  An inductance measurement circuit is a Maxwell bridge for measuring the inductance of low-Q coils (10 or less) by balancing the reactance of a fixed standard capacitor against that of the coil.

7-J)  A modulator circuit using a shunt-type full bridge balances out the r.f. input so that the r.f. carrier is always suppressed and only the upper and lower sidebands are present in the output signals.

8-F)  A Wien-bridge RC oscillator circuit for frequency stabilization employs one tube, V1, as an oscillator and a second, V2, to provide a frequency-selective, 180-degree feedback signal.

9-1)  A full-bridge rectifier is employed to obtain full-wave rectification of an a.c. signal.

10-H)  A resistance measurement circuit in the form of a Wheatstone bridge employs a calibrated potentiometer to indicate the value of an unknown high resistance when the bridge is balanced.




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About RF Cafe

Kirt Blattenberger - RF Cafe Webmaster

1996 - 2024


Kirt Blattenberger,


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 nice lady's voice announced "You've Got Mail" when a new message arrived...

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