The millions of people who purchased or homemade these inexpensive reliable receivers created the mass listening audience for the first radio broadcasts , which began around However it continued to be used by youth and the poor until World War 2.
The crystal radio used a cat's whisker detector , invented by Harrison H. Dunwoody and Greenleaf Whittier Pickard in , to extract the audio from the radio frequency signal. Only particular sites on the crystal surface worked as detector junctions, and the junction could be disrupted by the slightest vibration.
So a usable site was found by trial and error before each use; the operator would drag the cat's whisker across the crystal until the radio began functioning. Frederick Seitz, a later semiconductor researcher, wrote:. Such variability, bordering on what seemed the mystical, plagued the early history of crystal detectors and caused many of the vacuum tube experts of a later generation to regard the art of crystal rectification as being close to disreputable.
The crystal radio was unamplified and ran off the power of the radio waves received from the radio station, so it had to be listened to with earphones ; it could not drive a loudspeaker. During the wireless era it was used in commercial and military longwave stations with huge antennas to receive long distance radiotelegraphy traffic, even including transatlantic traffic. However it still had poor selectivity compared to modern receivers. Beginning around continuous wave CW transmitters began to replace spark transmitters for radiotelegraphy because they had much greater range.
The first continuous wave transmitters were the Poulsen arc invented in and the Alexanderson alternator developed , which were replaced by vacuum tube transmitters beginning around The continuous wave radiotelegraphy signals produced by these transmitters required a different method of reception. However the new continuous wave radiotelegraph signals simply consisted of pulses of unmodulated carrier sine waves. These were inaudible in the receiver headphones.
To receive this new modulation type, the receiver had to produce some kind of tone during the pulses of carrier. The first crude device that did this was the tikker , invented in by Valdemar Poulsen. In Reginald Fessenden had invented a better means of accomplishing this.
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Thus the "dots" and "dashes" of Morse code were audible as musical "beeps". A major attraction of this method during this pre-amplification period was that the heterodyne receiver actually amplified the signal somewhat, the detector had "mixer gain". The receiver was ahead of its time, because when it was invented there was no oscillator capable of producing the radio frequency sine wave f O with the required stability. The heterodyne receiver remained a laboratory curiosity until a cheap compact source of continuous waves appeared, the vacuum tube electronic oscillator  invented by Edwin Armstrong and Alexander Meissner in The heterodyne oscillator is the ancestor of the beat frequency oscillator BFO which is used to receive radiotelegraphy in communications receivers today.
The heterodyne oscillator had to be retuned each time the receiver was tuned to a new station, but in modern superheterodyne receivers the BFO signal beats with the fixed intermediate frequency , so the beat frequency oscillator can be a fixed frequency. Armstrong later used Fessenden's heterodyne principle in his superheterodyne receiver below. The Audion triode vacuum tube invented by Lee De Forest in was the first practical amplifying device and revolutionized radio.
The amplifying vacuum tube used energy from a battery or electrical outlet to increase the power of the radio signal, so vacuum tube receivers could be more sensitive and have a greater reception range than the previous unamplified receivers. The increased audio output power also allowed them to drive loudspeakers instead of earphones , permitting more than one person to listen. The first loudspeakers were produced around These changes caused radio listening to evolve explosively from a solitary hobby to a popular social and family pastime.
The development of amplitude modulation AM and vacuum tube transmitters during World War I, and the availability of cheap receiving tubes after the war, set the stage for the start of AM broadcasting , which sprang up spontaneously around The advent of radio broadcasting increased the market for radio receivers greatly, and transformed them into a consumer product.
Step 1: The Radio Drama Script
In the early radios the multiple tuned circuits required multiple knobs to be adjusted to tune in a new station. One of the most important ease-of-use innovations was "single knob tuning", achieved by linking the tuning capacitors together mechanically. A vacuum tube receiver required several power supplies at different voltages, which in early radios were supplied by separate batteries. By adequate rectifier tubes were developed, and the expensive batteries were replaced by a transformer power supply that worked off the house current.
Vacuum tubes were bulky, expensive, had a limited lifetime, consumed a large amount of power and produced a lot of waste heat, so the number of tubes a receiver could economically have was a limiting factor. Therefore, a goal of tube receiver design was to get the most performance out of a limited number of tubes. The major radio receiver designs, listed below, were invented during the vacuum tube era.
A defect in many early vacuum tube receivers was that the amplifying stages could oscillate, act as an oscillator , producing unwanted radio frequency alternating currents. The oscillations were caused by feedback in the amplifiers; one major feedback path was the capacitance between the plate and grid in early triodes. Edwin Armstrong is one of the most important figures in radio receiver history, and during this period invented technology which continues to dominate radio communication.
He invented the feedback oscillator , regenerative receiver , the superregenerative receiver , the superheterodyne receiver , and modern frequency modulation FM. The first amplifying vacuum tube, the Audion , a crude triode , was invented in by Lee De Forest as a more sensitive detector for radio receivers, by adding a third electrode to the thermionic diode detector, the Fleming valve. To give enough output power to drive a loudspeaker, 2 or 3 additional Audion stages were needed for audio amplification.
In addition to very low gain of about 5 and a short lifetime of about 30 — hours, the primitive Audion had erratic characteristics because it was incompletely evacuated. De Forest believed that ionization of residual air was key to Audion operation. Each Audion stage usually had a rheostat to adjust the filament current, and often a potentiometer or multiposition switch to control the plate voltage.
The filament rheostat was also used as a volume control. The many controls made multitube Audion receivers complicated to operate. By , Harold Arnold at Western Electric and Irving Langmuir at GE realized that the residual gas was not necessary; the Audion could operate on electron conduction alone.
These more stable tubes did not require bias adjustments, so radios had fewer controls and were easier to operate. The "soft" incompletely evacuated tubes were used as detectors through the s then became obsolete. The regenerative receiver , invented by Edwin Armstrong  in when he was a year-old college student,  was used very widely until the late s particularly by hobbyists who could only afford a single-tube radio. Today transistor versions of the circuit are still used in a few inexpensive applications like walkie-talkies.
In the regenerative receiver the gain amplification of a vacuum tube or transistor is increased by using regeneration positive feedback ; some of the energy from the tube's output circuit is fed back into the input circuit with a feedback loop. Regeneration could not only increase the gain of the tube enormously, by a factor of 15, or more, it also increased the Q factor of the tuned circuit, decreasing sharpening the bandwidth of the receiver by the same factor, improving selectivity greatly.
The tube also acted as a grid-leak detector to rectify the AM signal. Another advantage of the circuit was that the tube could be made to oscillate, and thus a single tube could serve as both a beat frequency oscillator and a detector, functioning as a heterodyne receiver to make CW radiotelegraphy transmissions audible. To receive radiotelegraphy, the feedback was increased until the tube oscillated, then the oscillation frequency was tuned to one side of the transmitted signal. The incoming radio carrier signal and local oscillation signal mixed in the tube and produced an audible heterodyne beat tone at the difference between the frequencies.
A widely used design was the Armstrong circuit , in which a "tickler" coil in the plate circuit was coupled to the tuning coil in the grid circuit, to provide the feedback. Regenerative detectors were sometimes also used in TRF and superheterodyne receivers. One problem with the regenerative circuit was that when used with large amounts of regeneration the selectivity Q of the tuned circuit could be too sharp, attenuating the AM sidebands, thus distorting the audio modulation.
A more serious drawback was that it could act as an inadvertent radio transmitter , producing interference RFI in nearby receivers. In nearby receivers, the regenerative's signal would beat with the signal of the station being received in the detector, creating annoying heterodynes , beats , howls and whistles. One preventative measure was to use a stage of RF amplification before the regenerative detector, to isolate it from the antenna. This was a receiver invented by Edwin Armstrong in which used regeneration in a more sophisticated way, to give greater gain. In the regenerative receiver the loop gain of the feedback loop was less than one, so the tube or other amplifying device did not oscillate but was close to oscillation, giving large gain.
The tuned radio frequency TRF receiver , invented in by Ernst Alexanderson , improved both sensitivity and selectivity by using several stages of amplification before the detector, each with a tuned circuit , all tuned to the frequency of the station. A major problem of early TRF receivers was that they were complicated to tune, because each resonant circuit had to be adjusted to the frequency of the station before the radio would work. A second problem was that the multiple radio frequency stages, all tuned to the same frequency, were prone to oscillate,   and the parasitic oscillations mixed with the radio station's carrier in the detector, producing audible heterodynes beat notes , whistles and moans, in the speaker.
From the standpoint of modern receivers the disadvantage of the TRF is that the gain and bandwidth of the tuned RF stages are not constant but vary as the receiver is tuned to different frequencies. The Neutrodyne receiver, invented in by Louis Hazeltine ,   was a TRF receiver with a "neutralizing" circuit added to each radio amplification stage to cancel the feedback to prevent the oscillations which caused the annoying whistles in the TRF.chronograffle.co.uk/horus-chosen-an-alternate-egypt-book-2.php
Radio receiver - Wikipedia
The reflex receiver , invented in by Wilhelm Schloemilch and Otto von Bronk,  and rediscovered and extended to multiple tubes in by Marius Latour   and William H. Priess, was a design used in some inexpensive radios of the s  which enjoyed a resurgence in small portable tube radios of the s  and again in a few of the first transistor radios in the s. In the reflex receiver the RF signal from the tuned circuit is passed through one or more amplifying tubes or transistors, demodulated in a detector , then the resulting audio signal is passed again though the same amplifier stages for audio amplification.
In addition to single tube reflex receivers, some TRF and superheterodyne receivers had several stages "reflexed". The superheterodyne , invented in during World War I by Edwin Armstrong  when he was in the Signal Corps , is the design used in almost all modern receivers, except a few specialized applications. In the superheterodyne, the " heterodyne " technique invented by Reginald Fessenden is used to shift the frequency of the radio signal down to a lower " intermediate frequency " IF , before it is processed.
By the s the superheterodyne AM broadcast receiver was refined into a cheap-to-manufacture design called the " All American Five ", because it only used five vacuum tubes: This design was used for virtually all commercial radio receivers until the transistor replaced the vacuum tube in the s. The invention of the transistor in revolutionized radio technology, making truly portable receivers possible, beginning with transistor radios in the late s. Although portable vacuum tube radios were made, tubes were bulky and inefficient, consuming large amounts of power and requiring several large batteries to produce the filament and plate voltage.
Transistors did not require a heated filament, reducing power consumption, and were smaller and much less fragile than vacuum tubes. The development of integrated circuits ICs in the s created another revolution, allowing an entire radio receiver to be put on a chip. ICs reversed the economics of radio design used with vacuum tube receivers.
The (Increasingly) Definitive Resource List for Aspiring Audio Dramaturges
Since the marginal cost of adding additional amplifying devices transistors to the chip was essentially zero, the size and cost of the receiver was dependent not on how many active components were used, but on the passive components; inductors and capacitors, which could not be integrated easily on the chip. As a result, the current trend in receivers is to use digital circuitry on the chip to do functions that were formerly done by analog circuits which require passive components. In a digital receiver the IF signal is sampled and digitized, and the bandpass filtering and detection functions are performed by digital signal processing DSP on the chip.
Another benefit of DSP is that the properties of the receiver; channel frequency, bandwidth, gain, etc. Many of the functions performed by analog electronics can be performed by software instead. The benefit is that software is not affected by temperature, physical variables, electronic noise and manufacturing defects.
Digital signal processing permits signal processing techniques that would be cumbersome, costly, or otherwise infeasible with analog methods. A digital signal is essentially a stream or sequence of numbers that relay a message through some sort of medium such as a wire. DSP hardware can tailor the bandwidth of the receiver to current reception conditions and to the type of signal. A typical analog only receiver may have a limited number of fixed bandwidths, or only one, but a DSP receiver may have 40 or more individually selectable filters. DSP is used in cell phone systems to reduce the data rate required to transmit voice.
A "PC radio" may not have a front-panel at all, and may be designed exclusively for computer control, which reduces cost. Some PC radios have the great advantage of being field upgradable by the owner. New versions of the DSP firmware can be downloaded from the manufacturer's web site and uploaded into the flash memory of the radio. The manufacturer can then in effect add new features to the radio over time, such as adding new filters, DSP noise reduction, or simply to correct bugs.
A full-featured radio control program allows for scanning and a host of other functions and, in particular, integration of databases in real-time, like a "TV-Guide" type capability. This is particularly helpful in locating all transmissions on all frequencies of a particular broadcaster, at any given time. Some control software designers have even integrated Google Earth to the shortwave databases, so it is possible to "fly" to a given transmitter site location with a click of a mouse.
In many cases the user is able to see the transmitting antennas where the signal is originating from. Since the Graphical User Interface to the radio has considerable flexibility, new features can be added by the software designer. Features that can be found in advanced control software programs today include a band table, GUI controls corresponding to traditional radio controls, local time clock and a UTC clock, signal strength meter, a database for shortwave listening with lookup capability, scanning capability, or text-to-speech interface. The next level in integration is " software-defined radio ", where all filtering, modulation and signal manipulation is done in software.
There will be a RF front-end to supply an intermediate frequency to the software defined radio. These systems can provide additional capability over "hardware" receivers. For example, they can record large swaths of the radio spectrum to a hard drive for "playback" at a later date. All-digital radio transmitters and receivers present the possibility of advancing the capabilities of radio. From Wikipedia, the free encyclopedia. The frequency spectrum of a typical radio signal from an AM or FM radio transmitter.
So You Wanna Create a Radio Drama?
It consists of a strong component C at the carrier wave frequency f C , with the modulation contained in narrow frequency bands called sidebands SB just above and below the carrier. How the bandpass filter selects a single radio signal S1 from all the radio signals received by the antenna. From top, the graphs show the voltage from the antenna applied to the filter V in , the transfer function of the filter T , and the voltage at the output of the filter V out as a function of frequency f.
The transfer function T is the amount of signal that gets through the filter at each frequency: Tuned radio frequency receiver. One of Marconi's first coherer receivers, used in his "black box" demonstration at Toynbee Hall, London, Write a customer review. Amazon Giveaway allows you to run promotional giveaways in order to create buzz, reward your audience, and attract new followers and customers. Learn more about Amazon Giveaway.
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As anyone in film will tell you, minutes spent in pre-production will save you hours later. Luckily, this area is rich with resources because nearly any sound-recording article, regardless of being radio drama specific or not, can help you out. There are basically four methods of recording a radio drama:. This is a fantastically innovative new production method, whereas producers collaborate with voice actors around the globe who record lines independently and then mix them together in post-production to create the final product. Here are some comments from listeners who have written in to me since this article was originally published.
We make extensive use of yahoogroups as well as Facebook for communication, casting calls, etc. VAs often work for multiple companies. We each have headphones and our mics on and I then have my actors zip up the files and email them over to me. Most of the companies post casting calls to it as well as their own yahoo groups.