The ultra-regenerative receiver has been used for many decades, especially at VHF and UHF, where it could offer a simple circuit and a relatively high level of performance. This detector was popular in its version of the vacuum tube for the first time days of receiving VHF in the late 1950s - early 60s. After that, it was used in simple circuits of the transistor version. This design was the cause of the hissing sound emitted by CB 27 MHz radio stations. Nowadays, super-regenerative radio is no longer so popular, although there are several applications that are still interesting to contemporaries.
History of radio
The history of the development of a super-regenerative receiver can be traced back to the very first days of its invention. In 1901, Reginald Fessenden used an unmodulated sinusoidal radio signal at a frequency offset from the carrier radio wave carrier and from the antenna for his rectifier crystal detector.
Later, during the First World War, radio amateurs began to take advantage of radio technologies, which provided sufficient quality and sensitivity of the transmission. Engineer Lucien Levy in France, Walter Schottky in Germany, and finally, the man attributed to the superheterodyne technique, Edwin Armstrong, solved the problem of selectivity and built the first working super-regenerative radio.
It was invented in an era when radio technology was very simple, and the super-regenerative receiver lacked the capabilities that are taken for granted today. The full-name superheterodyne radio receiver (superheterodyne) , the supersonic heterodyne wireless receiver, was an important step forward in the development of science and technology, although initially it was not widely used because it contained many valves, pipes and other bulky parts. And besides, at that time the radio was a very expensive pleasure.
Super Receiver Basics
The super regenerative receiver is based on a simple regenerative radio. It uses the second oscillation frequency in the regeneration cycle, which interrupts or dampens the main oscillations of the frequency. Damping usually works at frequencies above the audio range, for example, from 25 kHz to 100 kHz. During operation, the circuit has positive feedback, so even a small amount of noise will cause the system to oscillate.
The output of the RF amplifier in the receiver has positive feedback, i.e. part of the output signal is fed back to the input in phase. Any signal present will be amplified several times, and this can lead to an increase in the signal level a thousand times or more. Despite the fact that the gain is fixed, it is possible to achieve a level approaching infinity using feedback methods such as a circuit with a point of oscillation in a super-regenerative receiver with battery radio tubes.
Regeneration introduces negative resistance into the circuit, and this means that the total positive resistance decreases. And, in addition, with increasing gain, the selectivity of the circuit increases. When the circuit operates with feedback so that the generator operates sufficiently in the oscillation region, secondary low-frequency oscillation occurs. It destroys the frequency of high-frequency oscillations.
The concept was originally discovered by Edwin Armstrong, who coined the term βsuper recovery.β And this type of radio is called a super-regenerative lamp receiver. Such a scheme was used in all forms of radio from domestic broadcasting radio stations to televisions, high-precision tuners, professional radio stations, satellite base stations and many others. Almost all broadcast radios, as well as televisions, shortwave receivers and commercial radios, used the principle of superheterodyne as the basis for their work.
Transmitter Benefits
Superheterodyne radio has several advantages over other forms of radio. As a result of its advantages, the super-regenerative transistor receiver has remained one of the advanced methods used in radio technology. And despite the fact that today other methods come to the fore, the super-receiver is still very widely used, taking into account the functions that it can offer:
- Shorting selectivity. One of the main advantages of the receiver is its proximity to the selectivity that it can offer.
- Using filters with a fixed frequency, it can provide high-quality disconnection of the adjacent channel.
- The ability to receive multiple modes.
- Due to the topology, this receiver technology can include many different types of demodulators that are easily matched to requirements.
- Receive very high frequency signals.
The fact that the super-regenerative field-effect transistor receiver uses mixing technology means that most of the processing of the receiver is performed at lower frequencies, allowing itself to receive high-frequency signals. These and many other advantages mean that the receiver was in demand not only with the beginning of radioification, but will remain the same for many more years.
Super-regenerative field-effect transistor receiver
Let's figure it out. The principle of operation of a super regenerative receiver is as follows.
The signal that the antenna picks up passes into the receiver and enters the mixer. Another locally generated signal, often called a local oscillator, is fed to a different mixer port and the two signals are mixed. As a result, a new signal is generated at the sum and difference frequencies.
The output is transmitted to the so-called intermediate frequency, where the signal is amplified and filtered. Any of the converted signals that fall into the passband of the filter can pass through the filter, and they will also be amplified by the stages of the amplifier. Signals that go beyond the filter passband will be rejected.
Tuning the receiver is done simply by changing the frequency of the local oscillator. This changes the frequency of the incoming signal, the signals are converted and can pass through the filter.
Super regenerative receiver setup
Although it is more complex than some other types of radios, it has an advantage in terms of performance and selectivity. Thus, the tuning is able to remove unwanted signals more efficiently than other TRF (Tuned Radio Frequency) settings or radio stations that were used in the early days of the radio.
The basic concept and theory underlying superheterodyne radio include the mixing process. This allows you to transmit signals from one frequency to another. The input frequency is often called the RF input, while the locally generated signal of the generator is called the local generator, and the output frequency is called the intermediate frequency, since it is between the RF and the audio frequencies.
The block diagram of a basic super-regenerative receiver on a single transistor is as follows. In the mixer, the instantaneous amplitude of two input signals (f1 and f2) is multiplied, which leads to signals at the output of frequencies (f1 + f2) and (f1 - f2). This allows you to transmit the incoming frequency to a fixed frequency, where it can be effectively filtered. Changing the frequency of the local oscillator allows you to tune the receiver to different frequencies. Signals at two different frequencies can arrive at intermediate stages.
Tuning RF deletes one and takes the other. When signals are present, they can cause unwanted interference, masking the required signals if they appear simultaneously in the intermediate frequency section. Often in inexpensive radio stations, the harmonics of a local oscillator can be tracked at different frequencies, which leads to a change in the local oscillators when tuning the receiver.
A general block diagram of a super-regenerative receiver on a single transistor shows the main blocks that can be used in the receiver. In more complex radios, additional demodulators will be added to the basic block diagram.
In addition, some superheterodyne radio stations may have two or more transformations in order to provide increased performance, to improve the functioning of circuit elements, two or even three transformations can be used.
Where:
- tuning cap is a 15pF variable;
- inductor βLβ is nothing more than a 2-inch metal wire No. 20 curved in the shape of βUβ.
FM radio stations (88-108 MHz) need more inductance, and the lower half of the band (approximately 109-130 MHz) will require less, since it is above the FM range.
Automatic gain control 27MHz
The 27 MHz super-regenerative receiver is thought to have grown out of the need for wartime in a very simple disposable device with a high positive feedback gain. The solution to this was to allow tuned frequency oscillations to alternatively grow and be suppressed under the control of a second (quenching) generator operating at a lower radio frequency. Positive feedback was introduced by a variable potentiometer, which was used as follows.
The signal will increase in volume until the RF amplifier begins to oscillate. The idea was to cancel control until the wobble stopped. However, there was usually a significant hysteresis between position and effect. An increase in productivity could only be achieved if the promotion was stopped shortly before the start of the fluctuation, which required skill and patience.
In this device, the tunable amplifier begins to oscillate during the half-cycle of the oscillator waveform. During the βonβ part of the blanking cycle, the oscillations of the tuned amplifier grow exponentially from the noise of the circuit. The time to reach these oscillations to full amplitude is proportional to the Q value of the tuned circuit. Therefore, depending on the frequency of the blanking generator, fluctuations in the signal frequency can reach full amplitude (logarithmic mode) or be minimized (linear mode).
For radio control of the models, three main types of a 27 MHz super-regenerative receiver were used: a hard valve receiver, a soft valve receiver, and a transistor-based receiver.
A typical hard valve receiver circuit is shown.
Radio circuit for the range of 25-150 MHz
In this scheme, the superregenerative receiver in the range of 25 to 150 MHz is similar to the principle circuit of the MFJ-8100.
The first stage is based on a FET transistor connected to a common gate configuration. The stage of the radio frequency amplifier prevents radio frequency radiation from the antenna in both circuits. The superregenerative detector is based on a transistor connected to a common gate configuration. The trimmer adjusts the feedback gain to the point where the potentiometer provides smooth regeneration control.
The frequency range of this receiver is from 100 MHz to 150 MHz. Its sensitivity is less than 1 uV. Coils are wound on a removable frame with a diameter of 12 mm. Of course, regenerators and super regenerators are not the future of ham radio, but they still have a place in the sun.
315MHz Transmission Device
Here is a modern 315 RF super recovery module transmitter + receiver.
It provides a very cost-effective wireless solution with a maximum data transfer rate of up to 4 Kbps. And can be used as a remote control, electric doors, shutter doors, windows, remote control connector, remote control LED, stereo remote control and alarm systems.
Features:
- transmission range> 500 m;
- sensitivity -103 dB, in open areas, since it works with the method of amplitude modulation, the sensitivity to noise is higher;
- operating frequency: 315.92 MHz;
- working temperature: from -10 degrees to +70 degrees;
- transmission power: 25 mW;
- receiver size: 30 * 14 * 7 mm Transmitter size: 19 * 19 mm.
Tube ISM 433 MHz
The ultra-regenerative lamp receiver consumes less than 1 mW and operates in a 433 MHz non-contact industrial, scientific and medical network. In its simplest form, a super regenerative receiver comprises a radio frequency generator that periodically turns a blanking signal or low frequency signal on and off. When the damping signal is switched to the generator, the oscillations begin to increase with an exponentially growing shell. The use of an external signal at the nominal frequency of the generator accelerates the growth of the envelope of these oscillations. Thus, the duty cycle of the amplitude of the quenched oscillator varies in proportion to the amplitude of the applied radio signal.
In a superregenerative detector, the arrival of a signal begins radiofrequency oscillations earlier than in the absence of a signal. The super regenerative detector can receive AM signals and is well suited for detecting OOK (on / off-keyed) data signals. The super regenerative detector is a system of discredited data, i.e., each period counts and amplifies the radio frequency signal. In order to accurately restore the original modulation, the suppression generator must operate at a frequency slightly higher than the highest frequency in the original modulating signal. Adding an envelope detector followed by a low-pass filter improves AM demodulation.
The heart of the receiver contains a regular LC generator configured by Colpitts, operating at a frequency determined by the serial resonance L1, L2, C1, C2 and C3. When the device is turned off, the bias current Q1 extinguishes the generator. The cascade transistor Q2 and Q3 forms an antenna amplifier that improves the noise figure of the receiver and provides some radio frequency isolation between the generator and the antenna. To save energy, the amplifier only works with increasing oscillations.
Super-regenerative VHF circuit
The receiver consists of a 2N2369 transistor surrounded by fifteen components, which together are the high-frequency part. This assembly is the heart of the receiver. It provides both HF amplification and demodulation. The configured circuit installed in the collector of the transistor allows you to select the frequency.
The reaction kit was used very early in a short wave by tube radars. Then he was found in the famous "three transistors" in the talk mode of the 60s. Many 433 MHz remote control receivers still use it. Both stages on the BC337 are low-frequency amplifiers, the last of which provides power for headphones or a small speaker. An adjustable resistance of 22 kOhm adjusts the polarization of the 2N2369 transistor to get the best response point, combining sensitivity and low distortion, while avoiding vibrations that block its operation.
The sound frequency is restored through a 4.7 kΞ© resistor, then passes through a low-pass filter, which eliminates the high-frequency response switching. The first transistor BC337 provides pre-amplification of BF. A 4.7 nF capacitor located between its collector and its base acts as a low-pass filter, eliminating the high-frequency remainder and limiting the maxima. A resistance of 10 kΞ© controls the gain of the last stage and therefore the volume.
DIY radio assembly
For a super-regenerative 315 MHz do-it-yourself receiver, all components must be mounted on a printed circuit board and the tracks made using a cutter. A wide ground plan is indispensable for the (electrical) stability of the assembly. To facilitate copying on copper, print a photograph of the circuit, place it on the plate and, with an indication of the point, mark the ends of the tracks on the sheet. After checking the insulation of the tracks on the ohmmeter, the wiring is performed in accordance with the diagram.
Circuit components are easy to purchase at radio stores or online. Need a 50 or 100 ohm speaker.You can also use an 8-ohm loudspeaker, placing a step-down transformer installed on most of the old transistor stations, or connect an 8-ohm speaker, but the sound level will be lower. The assembly should remain compact with a good ground plan. It should not be forgotten that wires and connections have a self-acting effect at high frequencies. The chord coil has 5 turns of 0.8 mm wire (wired telephone connection). The capacitor is connected in series with the antenna in the second turn from above.
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The installation procedure for ultra-regenerative VHF receivers:
- Turn on the circuit. The supply current is about thirty milliamps.
- Turn the right adjustable resistor (volume) fully counterclockwise.
- Then you need to hear the noise in the headphones or speaker. If this is not the case, turn the adjustable impedance until a sound appears.
- Improve tuning to mid-range emissions to get good sensitivity with minimal distortion.
- To remove high noise, you need to reduce the antenna.
144 MHz superregenerative receiver circuit.
Precautions: since the unit emits interference, do not use it near another receiver.