science

SCR-300

SCR-300 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-300 rather than just read about it. In short: The SCR-300, designated AN/VRC-3 under the Joint Electronics Type Designation System, was a portable frequency modulated (FM) radio transceiver used by US Signal Corps in World War II. This backpack-mounted unit was the first radio to be nicknamed a "walkie talkie".

Key takeaways

SCR-300 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-300 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of SCR-300 from memory before moving on to harder problems.

Reference excerpt

The SCR-300, designated AN/VRC-3 under the Joint Electronics Type Designation System, was a portable frequency modulated (FM) radio transceiver used by US Signal Corps in World War II. This backpack-mounted unit was the first radio to be nicknamed a "walkie talkie".

History In 1940, Motorola (then the Galvin Manufacturing Company) received a contract from the War Department to develop a portable, battery powered voice radio receiver/transmitter for field use by infantry units. The project engineering team consisted of Daniel E. Noble, who conceived of the design using frequency modulation, Henryk Magnuski who was the principal RF engineer, Marion Bond, Lloyd Morris, and Bill Vogel. The SCR-300 operated in the 40.0 to 48.0 MHz frequency range, and was channelized. Along with other mobile FM tank and artillery radios such as the SCR-508 (20.0 to 27.9 MHz) and the SCR-608 (27.0 to 38.9 MHz), the SCR-300 marked the beginning of the transition of combat-net radio from low-HF (high frequency) AM/CW (amplitude modulated/ continuous wave) to low-VHF (very high frequency) FM. Although a relatively large backpack-carried radio rather than a handheld model, the SCR-300 was described in War Department Technical Manual TM-11-242 as "primarily intended as a walkie-talkie for foot combat troops", and so the term "walkie-talkie" first came into use. The final acceptance tests took place at Fort Knox, Kentucky in Spring 1942. The performance of the SCR-300 during those tests demonstrated its capacity to communicate through interference and the rugged quality of the design. Motorola was to produce nearly 50,000 of the SCR-300 units during the course of World War II. The SCR-300 saw action in the Pacific Theater, beginning in New Georgia in August 1943. Colonel Ankenbrandt informed General Meade that "they are exactly what is needed for front line communications in this theater". In his point of view, the main difficulty was keeping them supplied with fresh batteries. The SCR-300 saw heavy use in the Normandy invasion and the Italian campaign. It also became "key equipment" that helped deter confusion in the Battle of the Bulge. The British adopted the design of the SCR-300 for their own use from 1947 as the "Wireless Set No. 31".

Specifications

The SCR-300 was an 18-tube battery operated VHF battlefield radio half-duplex transceiver. It used an FM transmitter section and a double superheterodyne receiver. It incorporated an adjustable squelch circuit, an automatic frequency control circuit, a crystal controlled calibration circuit, easy to use tuning/channel selection, tuning lock to prevent accidental frequency changes, and radio relay or retransmission capability using two SCR-300 units and the appropriate cable assemblies.

Weight: With battery BA-70: 38.23 lb (17.34 kg) With battery BA-80: 32.23 lb (14.62 kg) Power supply requirements: Filaments: 4.5 volts Receiver plate: 90 volts Transmitter plate: 150 volts (using additional 60 volt battery) Antenna: AN-130-A: Two section flexible whip, 33 inches (84 cm) AN-131-A: Eight section flexible whip, 10 ft 8 in (325 cm) Frequency range: VHF between 40–48 MHz (7.5–6.2 m) Channel spacing: 200 kHz Channel Selection via "TUNING" control, channel display showing channel 0 (40.000 MHz) to channel 40 (48.000 MHz) Modulation: FM voice Vacuum tubes: 3A4 (2) 1T4 (6) 1L4 (5) 1R5 (1) 1A3 (1) 1S5 (3) RF Power output: 0.3 watts Frequency calibration (crystal oscillator) 4.3 MHz 10th harmonic (43.0 MHz) and 11th harmonic (47.3 MHz) marked on channel display - channel 15 (43.000 MHz) and halfway between channels 36 (47.200 MHz) and 37 (47.400 MHz) Range: approximately 3 miles (4.8 km) (varied considerably with terrain, location of transmitter and receiver, and antenna used)

War Department Technical Manuals TM 11-242 for Radio Set SCR-300-A (1945) TM 11-983 for PP-114 Vibrator power supply (1945) TM 11-637 for AN/VRC-3 (1944)

Illustrations

Worked examples

Example 1 — a first encounter with SCR-300

Start with the simplest possible case. Write down what SCR-300 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-300 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-300 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-300

In research: SCR-300 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-300 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-300 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Amateur radio transmitters, Military electronics of the United States, Military radio systems of the United States, so understanding it makes those chapters shorter.
In everyday life: Look for SCR-300 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.

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study SCR-300 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what SCR-300 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-300 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is SCR-300 in simple terms?

Why does SCR-300 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-300?

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-300.