physics

R-390A

R-390A is a physics 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 R-390A rather than just read about it. In short: The R-390A /URR is a general coverage HF radio communications receiver designed by Collins Radio Company for the United States Armed Forces. History The R-390A military shortwave radio receiver was the result of a project undertaken by the United States Army Signal Corps in 1954 to replace the existing R-390 receiver then in use.

Key takeaways

R-390A belongs to physics; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect R-390A to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of R-390A from memory before moving on to harder problems.

Reference excerpt

The R-390A /URR is a general coverage HF radio communications receiver designed by Collins Radio Company for the United States Armed Forces.

History The R-390A military shortwave radio receiver was the result of a project undertaken by the United States Army Signal Corps in 1954 to replace the existing R-390 receiver then in use. The R-390 had done its job so well that the Corps decided continued use of this type of receiver necessitated an improved, reduced-cost version. There are many references to the R390A in the open literature during this period; a picture of the receiver appeared in the May 1959 issue of QST. The total production of the R-390A (as determined by the high serial numbers noted) is over 55,000 units. Initial production started in 1955 and ran through approximately 1970, and then was restarted in 1984 by Fowler Industries for Avondale Shipyards. Manufacturers and their approximate production numbers are:

Companies which made spare modules, but not whole sets were Communications Systems Corp., Clavier Corp. and Hacking Labs.

Design The R-390A is a general coverage radio receiver capable of receiving AM, CW, and FSK signals. Its tuning range is from 500 kHz to 32 MHz, in thirty-two 1 MHz bands. The circuit is the superheterodyne type, double conversion above 8 MHz, below which triple conversion is used. It employs 23 vacuum tubes, a larger than normal count for most general-coverage receivers.

The receiver weighs 85 pounds (39 kg) and can be operated on 120-volt or 240-volt supplies. It fits neatly into a 10.5-inch-tall (270 mm) standard 19-inch rack. Tuning of the R-390A's radio frequency and intermediate frequency front end is synchronized by means of an ingenious mechanical system of racks, gears, and cams. When the front panel tuning controls are rotated, this system raises and lowers ferrite slugs in and out of the receiver's tuning coils. This ensures that all front-end circuits are tracked, meaning all circuits are tuned to the correct frequency to maintain excellent selectivity and sensitivity. The receiver's construction is modular for easy servicing. Each major area of the receiver is contained in easily removable subassemblies, and these can be repaired or replaced as needs be. Though the R-390A is mechanically and electrically complex, alignment and servicing were designed to follow simplified procedures published by the Signal Corps.

Use The R-390A was deployed to most branches of the US military and remained in general use through the 1980s. The last major update to its documentation was in 1984. As the military procured newer receivers, many R-390As were released to surplus while others were destroyed. Some receivers were retained by the services, however, when they found that the R-390A's vacuum tube circuitry could easily survive an electromagnetic pulse. There are reports, possibly apocryphal, that R-390A receivers are still in use aboard U.S. Navy submarines since the receiver can withstand the strong radio frequency fields found aboard ship. Many of the R-390As that exist today are in the hands of vintage amateur radio collectors and amateur radio operators who contend that few modern solid state communications receivers can equal its performance. There is a wealth of information, both printed and electronic, devoted to R-390A restoration and maintenance, as the R-390A is widely considered an example of the best of vacuum tube technology.

See also ART 13 transmitter ARC-5 BC-348 BC-654 Collins Radio Hammarlund super pro National HRO Vintage amateur radio 75A-4 and KWS-1

References

Illustrations

Worked examples

Example 1 — a first encounter with R-390A

Start with the simplest possible case. Write down what R-390A claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, 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 R-390A 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 R-390A 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 R-390A

In research: R-390A appears in physics 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 R-390A 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: R-390A is common in secondary-school and first-year university syllabi. It links to neighbouring topics Amateur radio receivers, Equipment of the United States Air Force, Military electronics of the United States, so understanding it makes those chapters shorter.
In everyday life: Look for R-390A 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 R-390A in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what R-390A 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 R-390A out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is R-390A in simple terms?

The R-390A /URR is a general coverage HF radio communications receiver designed by Collins Radio Company for the United States Armed Forces. History The R-390A military shortwave radio receiver was the result of a project undertaken by the United States Army Signal Corps in 1954 to replace the exis…

Why does R-390A matter?

Because it connects several physics 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 R-390A?

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 R-390A.