Homemade CB transmitter using Student lamps. Simple and cheap do-it-yourself radio transmitter Circuit diagram of a powerful FM transmitter on one lamp
Radio transmitting devices (Fig. 13.1 - 13.5) can be obtained by simply combining a low frequency amplifier (or generator) (ULF, LFO) and a high frequency generator (HHF). Block diagram of an amplitude modulation (AM) transmitter,…….
The 256 channel radio control receiver is one of two receivers designed to work with a 20 million code radio control unit. The receiver of the radio control unit is used for the device selected from.......
This portable UHF radio is of exceptional quality and reliability. Using reliable and regulated modules is the key to success and satisfaction. In addition, the modules used operate in the FM range, which ensures quality…….
Recently, “toy” radio stations produced in the People’s Republic of China have appeared on sale – the so-called “walkie-talkies”. They are distinguished by their simplicity and relatively good characteristics. The author’s radio station “SV STYLE ORIGINAL” NS-881…….
In order for the transmitter to have high efficiency and the receiver to have high stable gain, some specific requirements must be taken into account when designing VHF equipment. Loop coils must be made of copper…….
The sound, similar to the clinking of wine glasses and glasses, coming from a box with radio tubes, was reminiscent of preparations for a celebration. Here they are, looking like Christmas tree decorations, 6Zh5P radio tubes from the 60s... Let's skip the memories. A return to the ancient conservation of radio components was prompted by viewing the comments to the post
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including a circuit based on radio tubes and the design of a receiver for this range. Thus, I decided to supplement the article with the construction tube regenerative VHF receiver (87.5 - 108 MHz).
Retro science fiction, such direct amplification receivers, at such frequencies, and even on a tube, have not been made on an industrial scale! Time to go back in time and assemble a circuit in the future.
0 – V – 1, lamp detector and amplifier for telephone or speaker.
In my youth, I assembled an amateur radio station in the 28 - 29.7 MHz range at 6Zh5P, which used a receiver with a regenerative detector. I remember the design turned out great.
The desire to fly into the past was so strong that I simply decided to make a model, and only then, in the future, to arrange everything properly, and therefore I ask you to forgive me for the carelessness in the assembly. It was very interesting to find out how all this would work at FM frequencies (87.5 - 108 MHz).
Using everything I had at hand, I put together a circuit and it worked! Almost the entire receiver consists of one radio tube, and given that there are currently more than 40 radio stations operating in the FM range, the triumph of radio reception is invaluable!
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| Photo1. Receiver layout. |
The most difficult thing I encountered was powering the radio tube. It turned out to be several power supplies at once. The active speaker is powered from one source (12 volts), the signal level was enough for the speaker to work. A switching power supply with a constant voltage of 6 volts (twisted the twist to this rating) fed the filament. Instead of an anode, I supplied only 24 volts from two small batteries connected in series, I thought it would be enough for the detector, and indeed it was enough. In the future, there will probably be a whole topic - a small-sized switching power supply for a small lamp design. Where there will be no bulky network transformers. There was already a similar topic:
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| Fig.1. FM radio receiver circuit. |
This is so far only a test diagram, which I drew from memory from another old radio amateur’s anthology, from which I once assembled an amateur radio station. I never found the original diagram, so you will find inaccuracies in this sketch, but this does not matter, practice has shown that the restored structure is quite functional.
Let me remind you that the detector is called regenerative because it uses positive feedback (POS), which is ensured by incomplete inclusion of the circuit to the cathode of the radio tube (to one turn in relation to the ground). Feedback is called because part of the amplified signal from the output of the amplifier (detector) is applied back to the input of the cascade. Positive connection because the phase of the return signal coincides with the phase of the input signal, which gives an increase in gain. If desired, the tap location can be selected by changing the influence of the POS or increasing the anode voltage and thereby enhancing the POS, which will affect the increase in the transmission coefficient of the detecting cascade and volume, narrowing the bandwidth and better selectivity (selectivity), and, as a negative factor, with a deeper connection will inevitably lead to distortion, hum and noise, and ultimately to self-excitation of the receiver or its transformation into a high-frequency generator.
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| Photo 2. Receiver layout. |
I tune the station using a tuning capacitor of 5 - 30 pF, and this is extremely inconvenient, since the entire range is filled with radio stations. It’s also good that not all 40 radio stations broadcast from one point and the receiver prefers to pick up only nearby transmitters, because its sensitivity is only 300 µV. To more accurately adjust the circuit, I use a dielectric screwdriver to slightly press on the coil turn, shifting it relative to the other so as to achieve a change in inductance, which provides additional adjustment to the radio station.
When I was convinced that everything was working, I took it all apart and stuffed the “guts” into the drawers of the table, but the next day I connected everything back together again, I was so reluctant to part with nostalgia, tune in to the station with a dielectric screwdriver, twitch my head to the beat of musical compositions. This state lasted for several days, and every day I tried to make the layout more perfect or complete for further use.
An attempt to power everything from the network brought the first failure. While the anode voltage was supplied from the batteries, there was no 50 Hz background, but as soon as the mains transformer power supply was connected, the background appeared, however, the voltage instead of 24 now increased to 40 volts. In addition to high-capacity capacitors (470 μF), it was necessary to add a PIC regulator along the power circuits to the second (shielding) grid of the radio tube. Now the adjustment is done with two knobs, since the feedback level still varies over the range, and for ease of adjustment I used a board with a variable capacitor (200 pF) from previous crafts. As the feedback decreases, the background disappears. An old coil from previous crafts, of a larger diameter (mandrel diameter 1.2 cm, wire diameter 2 mm, 4 turns of wire), was also included in the kit with the capacitor, although one turn had to be short-circuited in order to accurately fall into the range.
Design.
In the city, the receiver receives radio stations well within a radius of up to 10 kilometers, both with a whip antenna and a wire 0.75 meters long.
I wanted to make a ULF on a lamp, but there were no lamp panels in the stores. Instead of a ready-made amplifier on the TDA 7496LK chip, designed for 12 volts, I had to install a homemade one on the MC 34119 chip and power it from a constant filament voltage.
An additional high-frequency amplifier (UHF) is requested to reduce the influence of the antenna, which will make the tuning more stable, improve the signal-to-noise ratio, thereby increasing sensitivity. It would be nice to do UHF on a lamp too.
It’s time to finish everything, we were talking only about the regenerative detector for the FM range.
And if you make replaceable coils on connectors for this detector, then
you will get an all-wave direct amplification receiver for both AM and FM.
A week passed, and I decided to make the receiver mobile using a simple voltage converter using a single transistor.
Mobile power supply.
Purely by chance I discovered that the old KT808A transistor fits the radiator from the LED lamp. This is how a step-up voltage converter was born, in which a transistor is combined with a pulse transformer from an old computer power supply. Thus, the battery provides a filament voltage of 6 volts, and this same voltage is converted to 90 volts for the anode supply. The loaded power supply consumes 350 mA, and a current of 450 mA passes through the filament of the 6Zh5P lamp. With an anode voltage converter, the lamp design is small-sized.
Now I decided to make the entire receiver a tube one and have already tested the operation of the ULF on a 6Zh1P lamp, it works normally at a low anode voltage, and its filament current is 2 times less than that of a 6Zh5P lamp.
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| Installation of a 28 MHz radio station. |
Addition to comments.
If you slightly change the circuit in Fig. 1, adding two or three parts, you will get a super-regenerative detector. Yes, it is characterized by “insane” sensitivity, good selectivity in the adjacent channel, which cannot be said about “excellent sound quality”. I have not yet been able to obtain a good dynamic range from a super-regenerative detector assembled according to the circuit in Fig. 4, although for the forties of the last century one could consider that this receiver has excellent quality. But we need to remember the history of radio reception, and therefore the next step is to assemble a super-super-regenerative receiver using tubes.
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| Rice. 5. Tube super-regenerative FM receiver (87.5 - 108 MHz). |
Yes, by the way, about history.
I have collected and continue to collect a collection of circuits of pre-war (period 1930 - 1941) super-regenerative receivers in the VHF range (43 - 75 MHz).
In the article " "
I have replicated the now rarely seen super regenerator design from 1932. The same article contains a collection of circuit diagrams of super-regenerative VHF receivers for the period 1930 - 1941.
TO ALL FREE ON THE AIR LIPETSK 3rd district!Autonode modulation in AM transmitters!!!
CITIZENS - USSR, probably few people did Autonode Modulation (AAM = 75% efficiency), due to its complexity. After reading a bunch of literature, I realized that it is worth it. Anode modulation is resting, and there is no talk of grid modulation at all. I offer AAM working schemes for your choice.
Where P is the output power;
Ra is the maximum power dissipated by the anode;
- efficiency amplifier
For example, with Ra = 125 W. (GK-71)
Efficiency = 25%.
With any grid modulation and with a regular (linear) AM signal, the amplifier operates in an undervoltage mode with low efficiency. (about 30%)!
The amplifier can deliver power:
Р=(125/(1-0.25))×0.25=42 W.
At AAM efficiency = 75% (GK-71)
Р=(125/(1-0.75))×0.75=375 watts.
In both cases, 125 watts are dissipated at the anode.
Consequently, the efficiency increases. amplifier from 25% to 75%, that is, 3 times. The power that can be removed from the amplifier increases by 9 times!
Principle of operation:
FIGURE 1
The main difference of the transmitter is the construction of a powerful final stage, which combines the functions of an RF amplifier and an anode modulator, which allows one to obtain high efficiency and power as with class B anode modulation.
This requires:
a) optimization of the final amplifier mode by using a (sliding) grid bias voltage.
b) creation of two stages of amplification of modulated oscillations with in-phase grid and anode (power supply of the anode circuit of the pre-terminal stage from the modulation choke).
c) driven by negative feedback at low frequency.
d) turning on the control lamp in the final stage (increasing the linear characteristic).
Scheme:
Figure 3 shows an AAM circuit with in-phase grid and anode modulation in the pre-final stage:
doubles the efficiency of the anode circuit of the pre-final stage in carrier mode, increases the peak power and excitation amplitude.
in the final stage, when the amplitude of the modulated oscillation UM changes, the anode voltage changes, i.e. additional anodic modulation occurs due to the anode current.
the constant component of the anode voltage changes in phase with the voltage on the grid (which contains an alternating low-frequency component created by the modulation choke TV2).
Applying a "sliding" grid bias voltage:
provides an increase in absolute value of the constant negative bias voltage Ec.
In carrier frequency mode, there is no additional positive voltage (connected in series) bias.
and with a large modulation depth, the positive bias voltage is maximum and compensates for the additionally introduced negative bias voltage (with an increase in the amplitude of the radio frequency excitation voltage),
The amplitude of the radio frequency voltage is selected in such a way that for all values of the total bias voltage, the operating mode of the generator remains slightly overvoltage.
To improve the linearity of the final stage and increase the dynamic characteristics, it is proposed:
change the voltage on the screen grid by changing the excitation voltage,
turning on the control lamp, supplying voltage to the screen grid at the moment the excitation voltage is applied. This produces an increment in the anode current proportional to the increment in the excitation voltage, i.e. the linear characteristic increases.
in the absence of excitation voltage, the anode current of L-3 is close to zero.
Negative feedback on the oscillatory voltage envelope,
By comparison with the voltage on the modulation choke along circuit C19, R12-R11 is supplied to the modulator (in this case, nonlinear distortions are reduced by three times, the dynamic characteristics of the modulator are increased).
Curves of changes in bias voltage and excitation voltage during the modulation period.
modulating voltage to the amplitude Usch.
Calculation: for GK-71
The power in carrier mode is set to P1=120 W. Let's choose GK-71:
Ea = 1800 V;
Ee = 400 V;
Ez = 50 V;
Eс = - 60 V;
S = 4.2ma/v = 0.0042 a/v;
Rnom.=250 W.
Ra additional = 125 W.
Let's take Ea nes. = 1800 v.
Let's start the calculation with maximum power mode:
at peak value U of modulating voltage
modulation coefficient t = 100%.
at the peak point θpeak=80°.
From the graph in Fig. 3 we find: at ϒpeak = 1.65 and cosθpeak. = 0.17; Epik.= 0.95
β1peak=α1 peak.×(1-cosθpeak.)=0.4
βо peak =αо peak.×(1-cosθpeak)= 0.24;
We determine the oscillatory power at the peak point:
P1pik. = 4P1nes.= 4×120=480W.
Anode voltage:
Ea peak.= 2×Ea non.=2×1800=3600v.
Fig.2
Graph for determining coefficients αо; α1; ϒ; β1 and ϒcosθ
Amplitude of oscillatory voltage on the circuit:
U peak.=Ѐpeak.×Ѐapik.=0.95×3600=3420v.
Amplitude of the first harmonic of the anode current:
Iα peak = 2Р1 peak/Uα peak = 480/3420 = 0.141 a (141 mA)
Required equivalent resistance of the oscillatory circuit: Req. opt=Uα/Iα peak = 3420/0.141=24256 ohm.
Constant component of the anode current:
Iα0 peak = Iα1 peak / ϒ peak = 0.141/1.65 = 86mA
Excitation voltage amplitude:
Upeak = Iα1 peak. /S x β1peak = 0.141/0.0042x 0.4 = 84v.
Bias voltage: Ec peak = Ec - Uv. peak. × cosθpeak. = - 60-84 × 0.17 = -74.2v.
Let's move on to calculating the mode at the instantaneous telephone point (set only if there is a modulating voltage):
those. mode at the midpoint of the modulation characteristic at a modulation depth of m = 100%.
in this case, the constant component of the anode current Iα0Т should have the same value as at the peak point, i.e. Iα0Т= Iα0Т peak.
As for the first harmonic of the anode current Iα1T, it should be two times less than at the peak point, therefore, we will have:
The result obtained suggests that at an instantaneous telephone point, the output stage of the transmitter operates in the mode of oscillations of the first kind, i.e. without anode current cutoff. In this case:
U inT = Iα1τ/ S =0.135/ 0.0042=32v
As we can see, the excitation voltage at the instantaneous telephone point should be:
5 times less than at the peak point,
and the negative offset decreases from - 77.7 to - 21v.
Finally at the lowest point of the modulation characteristic:
Uв=0, Ес = -21в.
Grid current at this point = 0
Let's move on to calculating the silent mode:
the voltage on the screen grid should decrease
therefore we accept. EU = - 50 v.
In order for the output stage in silent mode (in carrier mode) to have a high efficiency coefficient ηα along the anode anode circuit, we accept:
ξnes.=0.95; θnes = 75˚.
according to the graph in Fig. 2 we find β1nes = 0.35; ϒnes.=1.69; cosθnes = 0.26
The amplitude of the first harmonic current in silent mode will be equal to:
Iα1 carried =2Р1nes/ξnes.×Eα = 2×120/0.95×1800 =0.141a (141ma)
Constant component of the anode current:
Iα0 carried = Iα1 nes. / ϒnes.= 0.141/1.65=0.086a (86ma)
Exciting voltage amplitude:
Uv ins. = Iα1 ins. / S× β1nes. = 0.141/0.0042x0.35 = 96v
And bias voltage:
EU carried. = Ѐс- Uв нес.× cosθнс = -50 - 96 x 0.26 = - 75 in.
Many beginner (and not only) radio amateurs sooner or later become interested in the topic of transmitters. Indeed, the construction of VHF transmitters for the 88-108 MHz range is a fascinating and useful topic. Radio microphones, bugs and other devices can be assembled based on FM radio transmitters. There are many schemes for such devices, but finding a simple, powerful and at the same time stable UHF generator is a problem. After a long search, the choice fell on the following scheme.
The block was built on the basis of well-known circuits, but several modifications were added. The system works almost perfectly, the range is large, and the sound quality is good. BF240 transistors are used, but others can be installed here from the list below. The frequency is changed using a potentiometer.
List of semiconductor elements for assembly
- BB105G
- BB104G
- BF240 (BF199, BF195, BF183,184,185)
- 2n2369
- 1n4007
There is only one, very easy to wind, reel. Many people have problems with this, but anyone can wind 5 turns of 1 mm wire on a 5 mm mandrel.
As for shielding, the tin does its job. When tests were done without a screen, the frequency floated and responded to the approach of a hand. After applying the shielding, the circuit worked stably and no longer reacts to the approach of a hand.
Capacitors and power supply chokes can be useful to prevent self-excitation. This did not arise during testing, so the decoupling was not installed.
In addition to the output power level of the radio transmitter, a lot depends on the antenna. You can even receive a signal from it at a distance of up to 1 km if you place a long pin a couple of meters away.
AM signal transmitter
The XA994 microassembly is used in radio intercoms in the high and low frequency paths of the transmitter to generate and amplify HF signals
Radio microphone
The proposed device in conjunction with a radio broadcasting
VHF FM receiver can be used for wireless
transmission of voice messages over short distances or,
for example, as a baby monitor for remotely listening to noises and sounds in a children's room. The design feature is that the LC generator coil is made in the form of a printed circuit conductor.
Radio transmitter powered by 220 V network
This circuit, with a minimum of radio components, has fairly good characteristics:
high microphone sensitivity (you can hear the ticking of the wall clock in the room),
with an antenna length of 100 cm, the range is 500 meters (when using a mobile phone with built-in FM radio).
L1 - 6 turns of copper wire, 0.5 mm in diameter
VD1 - zener diode, type KS168 (any other voltage 6.8V can be used)
VT1, VT2 - transistors, type KT315, maybe KT3102, KT368.
A correctly assembled circuit should work immediately, the entire setup consists of adjusting the frequency by compressing and expanding the turns of coil L1 and selecting resistance R7 (100 Ohm - 1 kOhm) to achieve maximum power.
C4 can be supplied with a larger capacity, in which case it will smooth out pulsations even better. The power supply should be separated from the transmitter with an aluminum screen.
Retro transmitter
The small-sized radio transmitter from Radio No. 9 - 1957 probably served as the prototype for the creation of the “toy of the 60s”. An interesting fact is that “the transmitter was also tested on the 80 and 40 meter amateur bands, where good results were obtained.” Radio amateurs who decide to repeat the design (given above or from the article published below), naturally, should not forget about the type of modulation that is in these AM transmitters ...
Simple radio microphone
The range of the radio microphone is more than 300 meters outdoors. Despite the low supply voltage, the 3V radio microphone is quite powerful, the signal is confidently pressed from it to the radio receiver across 3 floors of the building. The frequency range of the radio microphone is from 87 to 108 MHz. Radio signal reception is possible on any FM radio receiver.
The coil (L1) is 3mm in diameter, has 5 turns of copper wire with a diameter of 0.61mm. The antenna length should be half or a quarter wavelength (for 100 MHz - 150 cm and 75 cm). By changing the width of the turns of coil L1, tune the radio microphone to the range from 87 to 108 MHz.
Source - http://www.hobby-hour.com/electronics/wireless_microphone.php
Simple CW transmitter
Transmitter output power is about 1 watt. Quartz is used from the RSIU station. Coils L1 and L2 are wound directly on the resonator body, the turns ratio is 5:1. To operate in the 3.5 MHz range, coil L1 must have an inductance of 25-29 µH, and for operation in the 7 MHz range - 7-8 µH. The tap is made from 1/3 to 1/5 of the turns of L1. The circuit is tuned by C2 and the antenna is tuned by C3. The circuit can be assembled using more modern transistors KT606, KT904, etc., by reversing the polarity of the power supply.
Simple QRP CW transmitter
VHF FM low power radio transmitter
In essence, this circuit can be classified as a radio microphone with an increased range of signal reception. The device is intended
to transmit an audio signal over a certain distance, using a frequency in the VHF-FM range 88-108 MHz. In this case, signal reception is possible on a VHF-FM broadcasting receiver operating in
corresponding frequency range. It should be noted that the output power of devices for this purpose is strictly regulated and cannot exceed 0.01 W. However, when setting up and fine-tuning this circuit, it is theoretically possible to reach 0.3-0.5 W.
Simple FM transmitter
The signal from the microphone is fed to the base of transistor VT1 through the isolation capacitor C1 (10 μF). VT1 acts as an AF amplifier and at the same time as an RF generator; as a result, we receive an FM signal at the transmitter output.
L1 - determines the frequency range of the transmitter, the coil has a diameter of 7 mm, the wire diameter is 0.3...0.35 mm, the number of turns is 7, after winding the coil must be pulled out to a length of 15 mm.
The collector of transistor VT1 is connected to antenna L2 (antenna), L2 has a winding diameter of 6 mm, the antenna is wound with a wire with a diameter of 0.35...0.5 mm. The antenna length is approximately 25...30cm. When winding, you should get a spring.
The transmitter range is 100 meters; when adjusting the transmitter range, compress or extend the L1 coil.
AM transmitter with a power of 25 W
