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 reel, very easy to wind. 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 occur 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.
Greetings Anton! I am gradually finishing the generator, all that remains is to think about the location of the antenna communication circuit, mounting the antenna (a quarter-wave pin from the radio receiver) directly on the transmitter body and installing a screen between the coils. I assumed that the stability of the electronically coupled circuit would be higher than that of the Huth-Kühn circuit, because in cx. with an electronic connection, the anode circuit influences the grid circuit much less than in the cx. Huth-Kühn (hence the influence of the load on the generating grid circuit will be weaker), especially if the anode circuit is tuned to a higher harmonic, which cannot be done in cx. Khut-Kyun. In any case, theoretically, cx. Hut-Kuhna will have better frequency stability than any single-circuit oscillator circuit. I consider it incorrect and pointless to compare a quartz oscillator with quartz-free ones, because So it is clear that the frequency stability when using a quartz resonator will be much higher than when using a conventional inductor. When using quartz, it will not be possible to carry out broadband FM, only narrowband. And to play music you need a broadband FM, so I won’t use a quartz oscillator. It’s good that you have a frequency meter, you can measure everything. I don’t have one and I determine stability by ear, subjectively. 12 years ago I assembled a two-stage transmitter: a 6n3p double-circuit generator and a second 6p15p stage. A clean, powerful signal without AC background, no interference on the range (only not all FM stations could be listened to in close proximity to the transmitter; when moving away from the transmitter everything was fine), and did not interfere with television either. When working for about 1-1.5 hours, the local oscillator frequency of the pocket receiver went away faster, and the transmitter generator stood rooted to the spot at one frequency (when receiving on a stationary receiver, subjectively by ear), with an unstabilized power source. I'm not going to broadcast around the clock, so the current stability is enough for me. I would like to clarify the experimental conditions: what lamps were used to collect cx. Hut-Kühn and Shembel, what supply voltages were supplied, what kind of load it was and how it was connected to the generators, at what frequency the generators operated and whether frequency multiplication was used in cx. Shembel (scheme with electronic communication)? How much was the anode circuit detuned relative to the grid circuit in cx. Hut-Kyuna? Have you observed the conditions for high-frequency installation: place the coils and inductors at a distance of at least their diameter from conductive surfaces; The coils of the anode and grid circuits should be placed perpendicularly, as far as possible from each other (but at the same time it is necessary that the connecting conductors be of a minimum length, as short as possible), a screen should be placed between the coils or one of the coils should be shielded. The parts of the input (grid) and output (anode) circuits also need to be separated from each other. To achieve maximum frequency stability, it is necessary to reduce the anode voltage; in the grid circuit of both generators, it is advisable to use coils made of silver-plated wire wound on a frame made of RF ceramics. It is better to connect the auto-bias chain, consisting of a capacitor and resistor connected in parallel, not to the upper end of the grid circuit, but to the middle of the coil. Select a higher resistance of the resistor in the auto-bias circuit. Anode circuit in cx. with electronic communication (shembel scheme) tuned to the 3rd harmonic. In сх. Shembel needs to include HF chokes in the filament circuit (did you have them? In the Hut-Kühn scheme, such chokes are not needed) and it is extremely undesirable to use triodes in this circuit, as well as pentodes, in which the protective grid is connected inside the lamp to the cathode. In сх. Hut-Kühn is better to use triodes. Anode circuit in c. Hut-Kühn should be detuned as much as possible relative to the grid in the direction of increasing the frequency of the anode. Capacitance of the capacitor, incl. between the anode and the grid in cx. Khut-Kyuna should be as small as possible, the smaller the better, Anton, what kind of capacity did you have? Below I wrote that after the experiments I want to tune the Hut-Kühn generator to a lower frequency and apply multiplication (tripling), because the lower the frequency of the generator, the higher its frequency stability. It would be interesting to compare the stability of the gene frequency using a frequency meter. Hut-Kyun at 32 MHz and 96 MHz, subject to all requirements for assembly and power supply of the generator. And one more thing: it is better to take the filament voltage of the generator lamp low, somewhere around 5.9-6.0 V. In the amplification stage it must be 6.3 V. One of the filament wires must be grounded, and in the power supply, and not in the transmitter . Connect the heat from the power supply with two single-core wires twisted together and covered with a shield. In parallel with the filament winding, you need to connect a capacitor with a capacity of 1000 pf, and also connect a 100-500 pf capacitor between the two filament blades in the lamp panel. In general, my goal is to assemble a simple, effective VHF generator with a minimum of parts and more or less acceptable frequency stability (subject to short-term operation), which can then be used as a master in a 2.3 or more cascade transmitter, both with frequency multiplication and without him.
While still students, we had fun by generating electromagnetic NE waves and modulated them in amplitude. Naturally illegal. To put it simply, we built it with a friend tube radio transmitters and aired them on NE band. But at that time tube receivers classical folk music has already begun to fade into oblivion prefix – hurdy-gurdy for 6p3s, connected to the sound cascade tube receiver was no longer relevant. That is, not having a tube receiver at home, to go on air, a full-fledged radio transmitter, not a prefix. Semiconductors were in short supply, but radio tubes there were rubble - it was full of dirt all around. And then my friend and I decided to do two tube transmitters- one of which is my copy, is still kept on my mezzanine as a relic and memory of those dark pre-computer times.
Young people then did not have the virtual world and social networks, but only a TV with two channels, a football ground, a bicycle, a tape recorder, and three sevens port wine. Standard set of entertainment of that time. I don't judge whether this is good or bad. It was just like that then.
Beginning of construction of the CB transmitter.
In the beginning, in fact, we built and tested one radio transmitter- my copy. The diagram was compiled by us from different parts of different sources and was constantly being reworked to fit the available parts. Parts were obtained from everywhere - exchanged, bought and begged from friends. For example power supply transformer was exchanged, as I remember now, for a new pump from a bicycle from one grandfather. Transmitter It was redesigned several times until it was finally finalized, optimized in terms of the number of parts and structurally designed on a wooden chassis.
CB transmitter antenna.
Transmitter antenna served as a 10-meter wire suspended at a height of about 2 meters on insulators above the roof of a five-story building between two wire radio masts installed on the same roof. That is, the wire was located next to two standard radio broadcast wires, which seemed to mask the antenna. The descent was carried out with an antenna (television) cable, passed into the mast pipe and skillfully carried through the attic of the five-story building and the exhaust shaft directly into the apartment.
CB transmitter parameters.
The transmitter operated at a frequency of about 1000 kHz. All this is of course conditional - according to the receiver’s arrow in the middle of the CB range. I conducted the reception on the radio " Selga 405" - mainly when transmitter testing. After 12 at night he turned on a tape recorder with music connected to transmitter and went out into the street with “Selga” hidden under his jacket. Listening was carried out using one earphone. And so I walked around the city at night, like a special agent on a secret mission - checking the range and quality of reception. My friend sometimes went with the same task, but in his own area - 1 km from me. To control the quality of the transmission it was possible longer - I slowed down the tape recorder motor. So the cassette playing time increased from 30 minutes to 1 hour. We were pleased with the test results. There was a reception in all parts of our area. True, it is much worse on the outskirts. Probably due to not very good antenna. Interference in those days on the NE band it was not enough - not like now, with the massive appearance of switching power supplies and other emitting crap. So basically our transmitter covered the planned area.
The first radio communication on the northeast.
In general, after a series of tests, we then built second transmitter according to the completed sketches and diagrams. It differed from the first one in a 6p15p lamp in the modulator, a power transformer and some design details. Having achieved a coincidence of frequencies - made the first radio communication. We greeted each other on the air and began to take turns yelling like idiots into the microphones, “race - race, race two three, how can you hear the reception.” Scientifically, “adjusting the modulation depth” is called: -). And for some reason, then we didn’t care that we were sitting on the broadcast CB band and in broad daylight we were quacking like fools “all over Ivanovo” from our five-story buildings. Two unafraid idiots :-) . Of course, I wouldn’t allow myself that now. But then, it was cool!
All this fuss with building and testing the transmitter, together with frequent interruptions, took time - probably about a year.
The call sign of my transmitter was “Orion”, the call sign of my friend’s transmitter was “Impulse”. Later we played music after 12 at night. There were no “pro-life” conversations, just like every day as a student at a technical school.
The further fate of the transmitter.
Objectively speaking, at first it was very cool, but over time I quickly got tired of it. Actually myself the process of building a transmitter for the CB range turned out to be much more interesting than playing several dozen tape cassettes on air.
Then my friend went to study in another city, where he stayed. Mine transmitter he bequeathed it to his younger brother, a dunce, who immediately dismantled it into parts along the way. And I played the music a little more and abandoned the matter. But sometimes, I get it from the mezzanine transmitter and like in the good old days, after 12 at night I turn on music for half an hour, inserting the call sign “Orion” into the pauses.
This is a bit of a sad story two tube pirate radio transmitters on the CB broadcast band in one small county town.
Transmitter interference.
Regarding the fact that we could have been “involved” by the relevant authorities: they could! But somehow it went unnoticed. Toli transmitter power is low, perhaps no one complained about interference, or interference They didn't really bother anyone. Another plus is that transmitter master oscillator made not according to the classic Sharman three-point scheme with a bunch of harmonics, but according to the “ GPD Shadsky" - an excellent circuit with a minimum of harmonics ( Radio magazine No. 1, 1963 Page 20). By the way, this is very clearly visible on the computer monitor screen - Receiver SDR. Really, when rebuilding the transmitter only one main peak runs across the range and only pair of harmonic peaks.
Transmitter power amplifier.
The transmitter power could be increased. Later, I had the idea to assemble an amplification stage - attachment on a 6p45 lamp according to the classic single-cycle circuit, but didn’t get around to it. Although, somehow for testing, I soldered with a surface-mounted installation additional stage on another one lamp 6p14p– I liked the result. Transmission range increased significantly. But for some reason it didn’t catch on - I was too lazy to improve this amplifier constructively. Although, in principle, it was possible - there would be room for 6p14p on the chassis.
Circuit diagram of the CB transmitter.
An ULF, also known as a modulator, is assembled on lamp L1, L2. Basically UCH scheme Can be any other lamp.
A master oscillator (GPA) is assembled on lamp L3 smooth range generator) according to Shatsky's scheme. Just a wonderful circuit that produces one clear carrier peak and a couple of weak harmonics at the output. Compared to a three-point generator, it’s “heaven and earth.”
An output signal power amplifier is assembled on lamp L4.
L1 – Generator circuit coil, setting the transmitter frequency. 75-100 turns on the frame from the IF circuit of a USSR TV. The coil is in a standard aluminum screen. *2 standard ferrite cores are screwed into the coil - specifically for this transmitter.
Variable capacitor, connected in parallel L1 – adjustment of the transmitter according to the range (capacitor from transistor radio receiver).
Coil L2 – P circuit. 100 turns (depending on antennas).
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, at 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 watts.
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-final 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 generator operating mode remains slightly overvolted.
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 with modulation depth t = 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 cut-off. 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.
