The super-regenerative receiver has been used for many decades, especially on VHF and UHF, where it could offer circuit simplicity and a relatively high level of performance. This detector was popular in its vacuum tube version for the first time in the days of VHF reception in the late 1950s and 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 27 MHz CB radios. These days, super-regenerative radio is no longer as popular, although there are several applications that are still of interest to contemporaries.
History of Radio
The history of the super-regenerative receiver can be traced back to the earliest days of its invention. In 1901, Reginald Fessenden used an unmodulated sine wave in his receiver for a rectifying crystal detector.a radio signal at a frequency offset from the carrier radio wave carrier and from the antenna.
Later, during the First World War, radio amateurs began to take advantage of radio technology, which provided sufficient transmission quality and sensitivity. Engineer Lucien Levy in France, W alter Schottky in Germany, and finally the man credited with 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 features that are taken for granted today. The superheterodyne radio receiver (superheterodyne) in its full name - 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 very expensive.
Super Receiver Basics
The super-regenerative receiver is based on a simple regenerative radio. It uses a second oscillation frequency in the regeneration cycle, which interrupts or dampens the main frequency oscillations. Vibration damping typically operates at frequencies above the audio range, such as 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.
RF amplifier outputin 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 repeatedly, and this can result in signal strength being amplified by a factor of a thousand or more. Although the gain is fixed, levels approaching infinity can be achieved using feedback techniques such as the swing-point circuit of a super-regenerative battery tube receiver.
Regeneration introduces negative resistance into the circuit and this means that the overall positive resistance is reduced. And, in addition, with increasing gain, the selectivity of the circuit increases. When the circuit is operated with feedback so that the oscillator operates sufficiently in the oscillation region, a secondary low frequency oscillation occurs. It destroys the frequency of the high frequency vibration.
The concept was originally discovered by Edwin Armstrong, who coined the term "super recovery". And this type of radio is called a super-regenerative tube receiver. Such a scheme has been used in all forms of radio from domestic radio broadcasting stations to televisions, high-precision tuners, professional communications radios, satellite base stations, and many others. Virtually all broadcast radios, as well as televisions, shortwave receivers and commercial radios, used the superheterodyne principle as the basis for operation.
Transmitter benefits
Superheterodyne radio has a number of advantages over other forms of radio. As a result of theiradvantages, the super-regenerative transistor receiver has remained one of the advanced methods used in radio technology. And while other methods are coming to the fore today, the super-receiver is still very widely used given the features it has to offer:
- Closing selectivity. One of the main advantages of a receiver is the proximity to the selectivity it has to offer.
- Using fixed frequency filters, it can provide high quality adjacent channel cutoff.
- Able to receive multiple modes.
- Due to the topology, this receiver technology can include many different types of demodulators that can be easily matched to suit requirements.
- Receive very high frequency signals.
The fact that the super-regenerative FET receiver uses mixing technology means that most of the receiver processing is done at lower frequencies, allowing itself to receive high frequency signals. These and many other advantages mean that the receiver has been in demand not only since the beginning of radio operation, but will remain so for many years to come.
Super Regenerative FET Receiver
Let's figure it out. The principle of operation of the super-regenerative receiver is as follows.
The signal that is picked up by the antenna passes through the receiver and into the mixer. Another locally generated signal, often referred to as a local oscillator, is fed into a different portmixer and the two signals are mixed. As a result, a new signal is generated at the sum and difference frequencies.
The output is transferred to the so-called intermediate frequency, where the signal is amplified and filtered. Any of the converted signals that fall within the passband of the filter can pass through the filter and they will also be amplified by the amplifier stages. Signals that fall outside the filter bandwidth 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 Tuning
Although more complex than some other types of radios, it has the advantage of performance and selectivity. Thus, tuning is able to remove unwanted signals more effectively than other TRF (Tuned Radio Frequency) settings or radio stations that were used in the early days of radio.
The basic concept and theory behind superheterodyne radio involves the mixing process. This allows signals to be transmitted from one frequency to another. The input frequency is often called the RF input, while the locally generated oscillator signal is called the local oscillator and the output frequency is called the intermediate frequency because it lies between the RF and audio frequencies.
The block diagram of a basic single-transistor super-regenerative receiver is as follows. ATmixer, the instantaneous amplitude of the two input signals (f1 and f2) is multiplied, resulting in output signals of frequencies (f1 + f2) and (f1 - f2). This allows the incoming frequency to be transmitted up 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 on two different frequencies can be sent to intermediate stages.
RF tuning removes one and takes another. When signals are present, they can cause unwanted interference by masking the desired signals if they appear simultaneously in the intermediate frequency section. Often in inexpensive radios, the harmonics of the local oscillator can track at different frequencies, resulting in a change in the local oscillators when tuning the receiver.
The overall block diagram of a single transistor super-regenerative receiver shows the main blocks that can be used in the receiver. More complex radios will add additional demodulators to the basic block diagram.
In addition, some ultraheterodyne radios may have two or more conversions to provide increased performance, two or even three conversions can be used to improve the functioning of circuit elements.
Where:
- tuning cap is variable 15pF;
- The "L" inductor is nothing more than a 2" 20 metal wire bent into a "U" shape.
FM radio stations (88-108 MHz) need moreinductance, and the lower half of the band (approximately 109-130 MHz) will require less since it is above the FM band.
27MHz Auto Gain Control
The super-regenerative 27 MHz receiver is believed to have grown out of a wartime need for a very simple one-off device with high positive feedback gain. The solution to this was to allow oscillations of the tuned frequency to alternatively grow and be suppressed under the control of a second (quenching) oscillator 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. The increase in productivity could only be achieved if progress was h alted shortly before the hesitation began, which required skill and patience.
In this device, the tuned amplifier begins to oscillate during the half cycle of the oscillator waveform. During the "on" part of the blanking cycle, the oscillation of the tuned amplifier rises exponentially from circuit noise. The time it takes for these oscillations to reach full amplitude is proportional to the Q value of the tuned circuit. Therefore, depending on the frequency of the damping generator, the signal frequency fluctuations can reach full amplitude (logarithmic mode) or be collapsed(line mode).
Three main types of 27 MHz super-regenerative receiver were used for radio control of the models: hard valve receiver, soft valve receiver and transistor based receiver.
A typical rigid valve receiver circuit is shown in the figure.
Radio circuit for 25-150 MHz band
In this circuit, the super-regenerative receiver on the 25-150 MHz band is similar to the circuit diagram of the MFJ-8100.
The first stage is based on the FET transistor connected to the common gate configuration. The RF amplifier stage prevents RF radiation from the antenna in both circuits. The super regenerative detector is based on a transistor connected to a common gate configuration. The trim 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 µV. The coils are wound on a removable frame with a diameter of 12 mm. Of course, regenerators and super regenerators are not the future of radio amateurs, but they still have a place in the sun.
315MHz transmission device
Here is a modern 315 RF super recovery transmitter + receiver module.
It provides a very cost-effective wireless solution with maximum data transfer ratesup to 4 Kbps. And can be used as remote control, electric doors, shutter doors, windows, remote control socket, LED remote control, stereo remote control and alarm systems.
Features:
- transmission range> 500m;
- sensitivity -103dB, in open areas because it works with amplitude modulation method, noise sensitivity is higher;
- working frequency: 315.92 MHz;
- working temperature: -10 degrees to +70 degrees;
- transmission power: 25mW;
- Receiver size: 30147mm Transmitter size: 1919mm.
433 MHz tube ISM
Ultra regenerative tube receiver consumes less than 1mW and operates on a non-contact 433MHz industrial, scientific and medical network. In its simplest form, a superregenerative receiver contains an RF oscillator that periodically turns on and off a "blank signal" or low frequency signal. When the damping signal is switched to the oscillator, the oscillations begin to build up with an exponentially growing sheath. The use of an external signal at the rated frequency of the generator accelerates the growth of the envelope of these oscillations. Thus, the duty cycle of the damped oscillator amplitude varies in proportion to the amplitude of the applied radio signal.
In a super-regenerative detector, the arrival of a signal starts RF oscillations earlier than when there is no signal. The Super Regenerative Detector can receive AM signals and is well suited forOOK (on/off-keyed) data signal detection. The superregenerative detector is a compromised data system, i.e. each period counts and amplifies the RF signal. To accurately restore the original modulation, the rejection 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 conventional LC oscillator configured by Colpitts, operating at a frequency determined by the serial resonance of L1, L2, C1, C2 and C3. When the device is turned off, the bias current Q1 extinguishes the generator. The cascaded transistors Q2 and Q3 form an antenna amplifier which improves the noise figure of the receiver and provides some RF isolation between the oscillator and the antenna. To save energy, the amplifier only operates when the oscillation increases.
Scheme of ultra-regenerative VHF
The receiver consists of a 2N2369 transistor surrounded by fifteen components that together form the high frequency part. This assembly is the heart of the receiver. It provides both HF gain and demodulation. A configured circuit installed in the collector of the transistor allows you to select the frequency.
The reaction set was used very early in the shortwave by tube radars. It was then found in the famous "three transistors" talk time of the 60s. Many 433MHz remote control receivers still usehis. Both stages on the BC337 are low-frequency amplifiers, the latter providing power for headphones or a small loudspeaker. The adjustable 22 kΩ resistance adjusts the polarization of the 2N2369 transistor to obtain the best response point, combining sensitivity and low distortion, while avoiding oscillation that blocks its operation.
The audio frequency is recovered through a 4.7kΩ resistor, then passed through a low-pass filter to eliminate high-frequency switching response. The first transistor BC337 provides BF pre-amplification. A 4.7nF capacitor placed between its collector and its base acts as a low-pass filter, eliminating the high-frequency residue and limiting the highs. The 10 kΩ resistor controls the gain of the last stage and therefore the volume.
DIY radio assembly
For DIY 315MHz Super Regenerative Receiver, all components must be installed on the PCB and the tracks are cut with a cutter. A wide ground plan is indispensable for the (electrical) stability of the assembly. To facilitate copying on copper, a photograph of the circuit is printed, placed on a plate and, with a dot, mark the ends of the tracks on the sheet. After checking the insulation of the tracks on the ohmmeter, the wiring is carried out in accordance with the diagram.
Circuit components are easy to purchase from radio shops or online. You need a 50 or 100 ohm speaker. You can alsouse an 8 ohm loudspeaker by placing a step down transformer found in most old transistor stations, or connect an 8 ohm speaker but the sound level will be lower. The assembly must 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 0.8mm wire (telephone line wiring). The capacitor is connected in series with the antenna at the second turn from the top.
The antenna consists of one piece of hard wire (1.5 mm2) about twenty centimeters long. No need to do more, "quarter wave" will disrupt the reaction. A 1 nF decoupling capacitor is required. The choke coil (high frequency blocking) is of the VK200 type. If the radio amateur cannot find it, you can make three or four turns of wire in a small ferrite tube. And you can choose a specific assembly scheme to your liking and in accordance with the wiring diagram.
Proper inclusion of the circuit
VHF Super Regenerative Receiver Installation Order:
- Turn on the circuit. The supply current is about thirty milliamps.
- Turn the right adjustable resistor (volume) fully counterclockwise.
- Next you need to hear the noise in the headphones or speaker. If not, turn the adjustable resistance until sound is heard.
- Improve mid-emission tuning to get good sensitivity with minimal distortion.
- Toto remove high noise, you need to reduce the antenna.
144 MHz ultra-regenerative receiver circuit.
Precautions: Since the unit emits interference, do not use it near another receiver.
