science

SCR-68

SCR-68 is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand SCR-68 rather than just read about it. In short: The SCR-68 (SCR was a military term meaning Set, Complete, Radio) was a military radiotelephone used by the US Army Signal Corps as an aircraft radio in the waning months of World War I. Due to its many problems, primarily its inability to communicate with other radios, like its ground component the SCR-67 or the larger truck mounted SCR-108, over large distances, the SCR-68 quickly became obsolete.

Key takeaways

SCR-68 belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect SCR-68 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of SCR-68 from memory before moving on to harder problems.

Reference excerpt

The SCR-68 (SCR was a military term meaning Set, Complete, Radio) was a military radiotelephone used by the US Army Signal Corps as an aircraft radio in the waning months of World War I. Due to its many problems, primarily its inability to communicate with other radios, like its ground component the SCR-67 or the larger truck mounted SCR-108, over large distances, the SCR-68 quickly became obsolete. Nonetheless, the SCR-68 was one of the first steps towards developing more effective messaging between pilots and commanders, even beyond military usage.

Capabilities The SCR-68 had a few distinct characteristics that separated the SCR-68 from other types of radio. The SCR-68 operated at 750 kHz (400 meter wavelength), using a long wire antenna reeled out behind the aircraft. It could receive and transmit messages over a maximum range of eighteen miles. The artillery observer (navigator) managed the SCR-68, receiving and relaying messages for the pilot. During World War I, most planes were two-person open-cockpit aircraft. Instead of communicating between themselves in the air, the pilot and the observer sent messages through the SCR-68 where the headphones would eliminate most outside noises. Like a private telephone line, the pilot and observer could communicate with each other; however, this action prevented the SCR-68 from receiving any transmissions.

Problems Advancements with the SCR-68 were marred by its flaws. Military tests by British soldiers reported the difficulty of getting the proper balance with the oscillating and control values. The SCR-68 range was reliable within a five-mile radius, a serious issue when the airplane needed to travel long distances. Another issue with the SCR-68 was the static noise that came from the “ripples” in the generator commutation. The noise was faint and was only considered a problem when receiving messages that exceeded 5 miles. It was later found that metal shielding placed around the wiring helped to prevent this problem.

Origins The US Army pushed for better technology to gain an advantage in World War I. The US Army asked private American companies to build a device that would establish better communication between military aircraft and themselves. Western Electric developed the SCR-68 that met qualifications: the radio was condensed to a size that could fit inside the airplane, simple for an Observer to use in flight, and the antenna would not drastically affect the movements of the aircraft. Another problem in the past included a communication device that eliminated the most disturbances from engine noise; the SCR-68 provided that by including a microphone and a sound-proof helmet. By the summer of 1918, approximately 3,000 units were manufactured and distributed to the US Army.

Parts

Radio Set Inside the suitcase-shaped box BC-11A was the circuit apparatus used for receiving and transmitting messages. The dials were used to control the frequency of the radio. The flip paddle switched the radio from receive to transmit and vice versa. The dimensions of the box were 17 inches by 10 inches by 7 inches and weighed 21 pounds.

Intercom The BC-10 (SCR-57) intercom control box for switching between onboard communication and ground communication.

Antenna The A-21 retractable antenna was located in the rear of the aircraft and was expanded by the air observer while in flight. It could reel out to 300 feet in length, was made out of two copper wires and weighed 19.5 pounds. Depending on the amount of antenna allowed behind the airplane, the antenna functioned at a wavelength of 750 kHz.

Generator The GN-1 wind-powered generator was located on the braces of the landing gear, to gather adequate wind power and not hinder any other parts of the aircraft. The generator, as well as three 22.5 volt batteries located in the BC-11, provided a plate voltage at 300 volts and a filament voltage at 30 volts. The wind-powered generator was not very efficient, requiring the airplane to travel at fast speeds in order for the generator to work properly.

Other • T-3 Single button Chest microphones for sending messages • HS-1 Headphones, to eliminate external sounds

See also Radiotelephone Air observer Navigator Signal Corps Radio

Notes

References Handbook, Radio pamphlet No.20 is the original manual.

External links https://web.archive.org/web/20090205020349/http://gordon.army.mil/OCOS/Museum/ScrComponents/scrPart1.asp SCR-list https://web.archive.org/web/20090206080333/http://gordon.army.mil/OCOS/Museum/bc1.asp BC-list http://www.footnote.com/image/#22404650 Gorrells History http://www.footnote.com/image/#24303018 post war report http://www.footnote.com/image/#24302991 installed in DH-4 http://uv201.com/Radio_Pages/Pre-1921/scr68.htm http://uv201.com/Radio_Pages/Pre-1921/Images/Development%20of%20Airplane%20Radiotelephone%20Set.pdf army.mil artillery report http://sdr.lib.umich.edu/cgi/pt?id=mdp.39015062770162 signal corps storage catalogue 1920 page 515

Worked examples

Example 1 — a first encounter with SCR-68

Start with the simplest possible case. Write down what SCR-68 claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to SCR-68 before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about SCR-68 ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of SCR-68

In research: SCR-68 appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses SCR-68 in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: SCR-68 is common in secondary-school and first-year university syllabi. It links to neighbouring topics 20th-century military history of the United States, Aviation in World War I, Military electronics of the United States, so understanding it makes those chapters shorter.
In everyday life: Look for SCR-68 outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study SCR-68 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what SCR-68 means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain SCR-68 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is SCR-68 in simple terms?

Why does SCR-68 matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study SCR-68?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on SCR-68.