Regenerative Receiver and Amplifier (also for beginners) |
Ernst Erb
![]() Officer
CH Articles: 5661
Schem.: 13755 Pict.: 31016 06.Mar.07 20:02 Count of Thanks: 45 |
Reply
|
You aren't logged in. (Guest)
1
Thanks to Ramon Gancedo, Madrid, Spain who decided to scan some pages of the RCA-Manual for Radiomuseum.org and Thomas Günzel, Ulm, Germany who did the OCR-Recognition I am (after correcting OCR - there may be still some small errrors) able to present you an article which shows the function, the build up and the operation of a principle often used in the radios of the mid 20ies, the Regenerative Receiver and Amplifier. The Regenerative Receiver is explained in this text and it is rather simple to operate. Well, you have to take care of the regeneration plus the tuning and the regeneration is also the volume control.
A TRF (Ernst Alexanderson, 1916) is basically the same but has more than one tuned radio-frequency amplifier. TRF is the short term for Tuned Radio Frequency. A Neutrodyne is the same as a TRF but there are circuits which care for operation without unwished oscillation due to high RF-amplification. By the way: Alexanderson (General Electric) was improving the high-frequency generator for longwave transmissions, beginning 1906, which made modulated (voice) radio broadcasts practical - see also Reginals Fessenden.
Regenerative Receiver and Amplifier
INTRODUCTION Radio communication is effected by means of electromagnetic waves which are radiated from the transmitting station and travel in all directions at the velocity of light. This velocity is 186,000 miles or 300,000 kilometers per second which will carry a radio signal seven times around the earth in a second. These waves cannot be heard because they have no mechanical effect on the ear drum and even if they did, the frequency would be so high that the ear could not respond to it. Sound waves have frequencies varying from about 16 cycles per second, which is the note produced by the largest organ pipe, up to about 20,000 cycles per second, which is the highest frequency to which the human ear will respond The velocity of sound waves in air is about 1100 feet per second so that sound waves have a length varying from an inch or so up to 60 or 70 feet. Radio waves are usually much longer, the usual broadcasting wavelength being 360 meters or 1180 feet. Therefore the frequency of these waves will be about 833.000 cycles per second.
Much confusion has arisen among non-technical people between wavelength and distance from which signals may be heard. Actually there is little connection between them. The distance from which signals can be heard depends upon the power of the transmitting station and the efficiency of both the transmitting and receiving apparatus.
THE RADIOLA RS
It has been designed to give strong, clear reproduction of voice and music without distortion, and to be sensitive, compact and easily operated. One of the principle features of this receiver is the use of a low current vacuum tube, the filament of which can be operated satisfactorily by an ordinary dry cell thus eliminating the need of a storage battery and the consequent necessity of charging periodically. Sensitivity and ease of operation combine to make the Radiola RS an ideal receiver for the unskilled operator and as one becomes proficient at its manipulation, he or she will be able to produce remarkable results.
For convenience to purchasers and to meet the requirements of the Fire Underwriters it is recom¬mended that the Radio Corporation of America antenna package, as specified above, be obtained since it contains approved equipment and directions for the installation of a proper out-door antenna.
Figure 3 The best antenna for all around receiving consists of a single wire size 14 B & S gauge installed 20 to 30 feet from the ground and extending horizontally 100 to 130 feet from the receiver. This antenna should be equipped with an approved protective device and installed in strict accordance with the rules of the National Fire Protection Association. When too much interference is experienced with the outdoor antenna of the dimensions given, it will be found advantageous to install a smaller antenna. This may be either indoors or outdoors, the outdoor installation in general giving slightly better results, but the indoor one is not subject to the rules of the underwriters and does not require a protective device. The small antenna should consist of not more than 25 feet of wire. Indoors, it may be concealed in a picture molding or any other con- venient place but slightly better results will be obtained if it is supported away from the wall. Such an antenna will produce almost as much strength of signal as a larger one but will tune much more sharply and thus reduce interference. When the above rules are followed and the techni- cal points mentioned above have been properly con- sidered, the antenna will give good signal strength and there will be no fire hazard. Figure 3 shows the complete antenna package equipment, type AD, and Figure 4 shows diagram- matically how an antenna should be installed. The center span of wire between insulators is the working span and is connected to the instrument by the "down lead" or lead-in wire. The protective device provides a discharge path from antenna to ground and thus protects the antenna during electri- cal storms.
The following quotations from the Underwriter's rules will be of value. "Each lead-in wire shall be provided with an approved protective device properly connected and located (inside or outside the building) as near as practicable to the point where the wire enters building". "The protector shall not be in the immediate vicinity of easily ignitible stuff or where exposed to inflammable gases, or dust, or flying combustible material." "The protective ground wire may be bare or insulated and shall be of copper or approved copper clad steel. If of copper the ground wire shall not be smaller than No. 14 and if of copper clad steel it shall not be smaller than No. 17. The ground wire shall be run in as straight a line as possible to a good permanent ground. Preference shall be given to water piping. Gas piping shall not be used for grounding protective devices. Other per- missible grounds are grounded metallic work in the building and artificial grounds such as driven pipes, plates, cones, etc". "The ground wire shall be protected against mechanical injury. An approved ground clamp shall be used wherever the ground wire is connected to pipes or piping." "The receiving equipment ground wire may be bare or insulated and shall be of copper or copper clad steel as in the case of the protective ground wire." "The receiving equipment ground wire may be run inside or outside the building. When receiving equipment ground wire is run in full compliance with the rules for protective ground wire, it may be used as the ground conductor for the protective device."
Figure 4
CONNECTING RADIOLA RS
The Antenna Lead-in
The Ground Wire
Connection of Filament or "A" Battery
Connection of "B" Battery
Connection of Telephone Headset OPERATION
General:
Control and Tuning:
The Filament Rheostat,
The Tuning Lever
The Tickler Knob
Hunting Signals:
Figure 5
Final Adjustment of Rheostat:
Regeneration: A vacuum tube has three electrical circuits connected with it, all of which are necessary for its operation. The first is the filament heating circuit composed of a battery to supply the current, a variable resistance commonly called a rheostat to control the current, the filament of the vacuum tube and the connecting wires. It is the function of this circuit to heat the filament, just as in an ordinary incandescent lamp, to the proper temperature when electrons are given off by the filament. These electrons are very small particles of electricity and have a negative charge. They are free to travel around inside the tube. The second circuit is the output circuit and is composed of the "B" battery, the telephone headset, the filament of the vacuum tube, the tickler coil, the plate of the vacuum tube and some of the electrons given off by the filament. The negative end of the battery is connected to one end of the filament while the positive end is connected to the telephone headset and through it to the plate of the vacuum tube. This makes the plate positive with respect to the filament and it therefore attracts the electrons which are given off by the filament so that instead of wandering around inside the tube, some of the electrons will reach the plate. These electrons then constitute a flow of negative electricity which is an electric current. The strength of this current will be directly proportional to the number of electrons reaching the plate. This will vary with the attractive force which depends upon the potential difference between the plate and filament or more simply upon the voltage of the "B" battery, and upon the supply of electrons which depends on the filament temperature and is usually kept constant. The third circuit is the input circuit and consists of the filament, part of the tuning circuit, the grid condenser and leak, the grid and the space between the grid and the filament inside the tube. When signals are being received, alternating currents flow in the tuning circuit causing differences of potential between the grid and filament. The grid is placed between the filament and the plate and is usually a helix of fine wire. When the grid is positive with respect to the filament it helps the plate to attract electrons and thus increases the plate current. When it is negative it decreases the plate current. Thus there is superimposed on the steady plate current, a small alternating current which has such a high frequency that neither the telephone receiver nor the human ear can respond to it. The frequency is so high that the current prefers to pass through the by-pass condenser instead of the telephone receiver. At the same time, by means of the grid condenser and leak, other potentials of lower frequency and corresponding to the changes in amplitude of the signals are being impressed on the grid and these produce changes in the steady plate current which flows through the telephone receivers and cause changes in the pull on the diaphragms thus producing audible sound. The high frequency-currents however are of the same shape as the currents in the tuning circuit and keep step with them. Therefore a coil of wire called the "tickler" is connected between the plate of the vacuum tube and the telephone headset and this coil is so located that the currents flowing in it can induce currents in the tuning circuit which add to those produced by the electro-magnetic waves intercepted by the antenna. Therefore, greater potentials are applied to the grid and greater changes of plate current are produced, which in turn produce a louder sound in the telephone receiver. It is possible to carry the above process too far, that is, enough potential may be applied to the grid from the tickler so that no incoming signal is necessary. The set then acts as a converter of direct current supplied by the "B" battery into alternating current and is said to be "oscillating". The radio frequency currents produced by the set will combine with those picked up by the antenna and will produce whistling noises called beat notes in the receiver. The music or speech may still be heard but will be mushy and muffled. But it should be remembered that whenever the receiving set is oscillating, that it is acting like a miniature transmitter and is radiating electro magnetic waves. Any other receiving set that maybe within range and which is tuned to the same frequency will pick up these waves. Therefore, if your set is adjusted to produce a beat note with a particular broadcasting station, your neighbor, who is listening to the same broadcasting station, will also hear the beat note and will be powerless to do anything about it even though it may ruin his enjoyment of the concert or speech. Therefore, never let your set oscillate when listening to a radio concert.
MAINTENANCE
Renewal of Vacuum Tubes:
Renewal of "A" Battery:
Replacing Grid Leak Condenser: OPERATING TROUBLE It is impossible to cover in detail all the possible operating troubles that may occur. The above instructions cover the usual renewals which may be made by the non-technical operator Troubles due to broken wires, loose connections, etc., are difficult to locate. If they occur, an experienced radio service man should be called in to locate and remedy the trouble. The following description and diagram of connections is included to facilitate trouble hunting. ELECTRICAL CIRCUIT Figure 6 gives the diagram of connections of the Radiola RS while Figure 7 is a view of the interior showing the apparatus mounted on the under side of the panel. The tuning circuit is of the well known single circuit type consisting of a variable inductance (A) in series with a fixed condenser (B), the latter, having two values of capacity which are available through two antenna binding posts.
Figure 6 The grid potential is taken off the whole inductance, the grid condenser and leak method of detection being used. The grid condenser and leak (C) are combined in one unit which is mounted in fuse clips. Two vacuum tubes are provided, one (F) being used as the detector while the other (U) is used as an audio frequency amplifier. The rheostat (V) is connected in the negative lead which is common to both tubes and it therefore controls the filament current to both tubes at the same time. Separate binding posts "+ Ai" and "+ A2" provide for the use of individual dry cells.
Figure 7 Regeneration is provided by an inductively coupled tickler consisting of a stationary winding (E) and a rotary winding (D) connected in series. Coupling is provided through the feeder windings (G) which are part of the tuning circuit. A by-pass condenser (H) permits the high frequency currents to pass the audio frequency transformer (J). The plate currents from the detector tube pass through the primary of the transformer and produce potentials in the secondary which are then applied to the grid of the amplifier tube (U) producing greater changes in the plate current than in that of the detector. This plate current from the amplifier passes through the telephone headset and produces the audible sounds. EE Feb 23, 2012: Added links for further reading. This article was edited 23.Feb.12 10:19 by Ernst Erb . |
|||
Joe Sousa
![]() Editor
USA Articles: 658
Schem.: 193 Pict.: 418 01.Jun.08 05:27 Count of Thanks: 39 |
Reply
|
You aren't logged in. (Guest)
2
Dear Ernst, this is a very good article. I would like to add a bit of clarification about the cause of oscillations from Miller Feedback capacitance. This article was edited 28.Feb.12 11:12 by Ernst Erb . |
|||
Ernst Erb
![]() Officer
CH Articles: 5661
Schem.: 13755 Pict.: 31016 23.Feb.12 10:45 Count of Thanks: 20 |
Reply
|
You aren't logged in. (Guest)
3
This post is added to help further if a reader gets this thread via a Search Engine. There are many more interesting articles, which can be found by clicking the tab "Papers" and then the different boards. You have a circumference of very theoretical to very practical contributions, like "hands-on" basic articles: "For Beginners: Prefixes and codes". A very good article on "Background hum with electrodynamic loudspeakers" etc. You also find different history articles like here about early tuning indicators and what was first needed for that. This article was edited 23.Feb.12 14:06 by Ernst Erb . 13455 from 25542
|