also called for operation on the 40 Lo range. In this case, it turns into a system of half-wave vibrators. The use of such an antenna on other bands is not practical due to the possibility of using more efficient antennas.
When working in urban conditions, the described antenna showed good results. It allows semi-
In recent years, supermodulation has been widely used in amateur radio designs. However, the desire to make maximum use of the energy capabilities of screen voltage modulation often leads to signal distortion. Practical testing of modulators with different modulating valves
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There are three options for characteristics that provide optimal communication conditions: depending on the operating conditions, you can get either maximum amplification of the correspondent’s signal (Fig. 2, a) or maximum attenuation of the interfering station (Fig. 2, b).
E. ELINEVICH, Talli (UR2CG)
power lengthens the straight section of the modulation characteristic.
Circuits that allow two-grid modulation are shown in Fig. 1 and 2. Essentially, they differ only in the types of lamps used and in the fact that in the circuit of Fig. 1 displacement is carried out due to the grid current.
When using two-grid modulation, all correspondents noted an increase in signal strength and a clear improvement in modulation quality and intelligibility. Long-term operation of transmitters on radio stations UA3RV and UA3RQ, as well as evaluation of signal quality by Soviet
and foreign correspondents, allow us to recommend the diagrams in Fig. 1 and 2 for repetition.
The following should be noted: it is advisable to power the filament of the modulating lamp from a separate source; the selection of the values of Rs and Ci" must be approached carefully, since an excessively large connection of grids can damage the L2 lamp or lead to an expansion of the signal bandwidth.
The most acceptable type of work should be considered the following mode:
at which during pauses the anode current is approximately 20% -25% of the telegraph current.
V. Tamboe (EA3RY)
Double grid CLC modulation
RECEIVER CASE
(6N7S, 6N6P, 6S19P, 6PZS) on transmitters that used GU-50, GU-29 and GK-71 lamps in the final stage showed that even a slight excess of the screen voltage leads to the appearance of nonlinear distortions and an expansion of the signal bandwidth.
In order to obtain 100% modulation, reduce nonlinear distortions and rationally use the advantages of supermodulation, the author used screen voltage modulation and simultaneous modulation on the control grid. In this case, the voltage on the screen grid and the RF voltage on the control grid change according to the same law. This condition makes a correction to the modulation (dynamic) characteristic. In addition, such modulation allows the peak power of the telegraph mode to be exceeded without unduly boosting the screen voltage. It should be noted that some reduction in screen voltage without compromising
“Where can I buy a housing for transistors in “Radio”, 1968, No. 6 and No. 9?” - a new receiver, the description of which many readers ask about.
As the chief designer of the Moscow EMA plant, T. Parafenyuk M. G. told us, the company has begun producing cases convenient for placing receivers of this type. Case size 152x90X36 mm. The internal projections and positioning of the mounting posts for the board and speaker are the same as in the widely used Sokol receiver. Therefore, the housing can be used as a backup to the factory receiver.
The body is made of impact-resistant bostyrene oxide in various colors. The kit, along with mounting screws and a scale, includes a description and instructions for setting up a superheterodyne amateur receiver with seven transistors.
The photo shows a general view of the body and cover of the receiver case.
RADKO No. 2 .1969 O 89
A simple circuit of an AM HF transmitter for the amateur 3 MHz band for a novice radio amateur: a detailed description of the operation and device
Proposed transmitter circuit does not contain scarce parts and is easily repeatable for beginning radio amateurs taking their first steps in this exciting, exciting hobby. The transmitter is assembled according to the classical design and has good characteristics. Many, or rather, all radio amateurs begin their journey with just such a transmitter.
It is advisable to start assembling our first radio station with a power supply, the diagram of which is shown in Figure 1:
picture 1:
The power supply transformer can be used from any old tube TV. The alternating voltage on winding II should be about 210 - 250 v, and on windings III and IV 6.3 v each. Since the load current of both the main rectifier and the additional one will flow through diode V1, it must have a maximum permissible rectified current twice as large as the other diodes.
Diodes can be taken of the modern type 10A05 (sample voltage 600V and current 10A) or, even better, with a voltage reserve - 10A10 (sample voltage 1000V, current 10A), when using more powerful lamps in the transmitter power amplifier, we need this reserve It can be useful.
Electrolytic capacitors C1 – 100 µF x 450V, C2, C3 – 30 µF x 1000V. If you don’t have capacitors with an operating voltage of 1000V in your arsenal, then you can make up 2 series-connected capacitors of 100 μF x 450V.
The power supply must be made in a separate housing, this will reduce the overall dimensions of the transmitter, as well as its weight, and in the future it will be possible to use it as a laboratory one, when assembling structures on lamps. Toggle switch S2 is installed on the front panel of the transmitter and is used to turn on the power when the power supply is under the table or on the far shelf, where you really don’t want to reach (can be excluded from the circuit).
Figure 2:
Modulator details:
C1 – 20mkfx300v, C7 – 20mkfx25v, R1 – 150k, R7 – 1.6k, V1 – D814A,
C2 – 120, C8 – 0.01, R2 – 33k, R8 – 1m variable, V2 – D226B,
C3 – 0.1, C9 – 50mkfh25v, R3 – 470k, R9 – 1m, V3 – D226B,
C4 – 100 µFx300V, C10 – 1 µF, R4 – 200k, R10 – 10k,
C5 – 4700, C11 – 470, R5 – 22k, R11 – 180,
C6 – 0.1, R6 – 100k, R12 – 100k – 1m
Electret microphone from a cassette recorder or telephone headset (tablet). The part of the circuit highlighted in red is necessary to power the microphone; if you intend to use only a dynamic microphone, then it can be removed from the design. Trimmer resistor R2 sets the voltage to + 3V. R8 – modulator volume control.
The output transformer is from a tube receiver or a TV of the TVZ type; you can also use vertical scan transformers TVK - 110LM2, for example.
The setting consists of measuring and, if necessary, adjusting the voltages at terminals (1) +60V, (6) +120V, (8) +1.5V of the 6N2P lamp and at terminals (3) +12V, (9) +190V 6P14P.
Figure 3:
Transmitter details.
C1 – 1 section gearbox 12x495, C10 – 0.01, R1 – 68k
C2 – 120, C11 – 2200, R2 – 120k
C3 – 1000, C12 – 6800, R3 – 5.1k
C4 – 1000, C13 – 0.01, R4 – 100k variable
C5 – 0.01, C14 – 0.01, R5 – 5.1k
C6 – 100, C15 – 0.01, R6 – 51
C7 – 0.01, C16 – 470 x 1000V, R7 – 220k variable
C8 – 4700, C17 – 12 x 495, R8 – 51
C9 – 0.01, R9 – 51
R10 – 51
The GPA coil L1 is wound on a frame with a diameter of 15 mm and contains 25 turns of 0.6 mm PEV wire. The inductor in the cathode of lamp L2 is factory-made and has an inductance of 460 μH. In my design, I used a choke from a TV, wound on an MLT - 0.5 resistor with a wire in a slot winding. Chokes L3 - L6 are wound between the cheeks on old-style VS-2 resistors and have 4 sections of 100 turns of PEL-2 wire with a diameter of 0.15 mm. Chokes L7 and L8 each have 4 turns of PEV wire with a diameter of 1 mm wound on top of resistors R8 and R9 MLT-2 with a resistance of 51 Ohms and serve to protect the final stage from self-excitation at high frequencies. The anode choke L9 is wound on a ceramic or fluoroplastic frame with a diameter of 15 - 18 mm and a length of 180 mm. PELSHO wire 0.35 turn to turn and has 200 turns, the last 30 turns in increments of 0.5 - 1 mm.
The L10 contour coil is wound on a ceramic, cardboard or wooden frame with a diameter of 50 mm and has 40 turns of PEL-2 wire with a diameter of 1 mm. When using a wooden frame, it should be well dried and varnished, otherwise, when exposed to high RF current, it will dry out, which will lead to deformation of the winding and possibly even a breakdown between the turns.
C17 is a double unit from a tube receiver with plates removed through one in a movable and fixed block.
Variable resistor R4 sets the bias on the control grid of the 6P15P lamp, and resistor R7 sets the bias for 6P36S lamps.
Relays can be of any type for a voltage of 12V with a gap between contacts of 1mm with a switching current of 5A.
Ammeter for current 100 mA,
The final stage is tuned to resonance using the minimum milliammeter readings.
The bias circuit is shown in Figure 4:
Figure 4:
Transformer T1, any step-down transformer 220v/12v with reverse connection. The secondary (step-down) winding is included in the filament circuit of the lamps, and the primary serves as a step-up winding. The output of the rectifier is about -120V and is used to set the bias of the lamps of the final stage of the transmitter.
Useful thing!
The figure above shows a diagram of the field strength indicator. This is a circuit of the simplest detector receiver, only instead of headphones, it has a microammeter, by which we can visually observe the signal level when tuning the transmitter to resonance.
The CLC modulator in TLG mode applies a negative voltage to the grid of the left half of lamp L2, which turns off the lamp. In this case, a large positive voltage from resistor R1 opens the right half of L2, which ensures that positive voltage is supplied to the screen grid L1. In the case of operation in the TLF mode, the low-frequency signal arriving at the grid of the left half of lamp L2 causes a change in its anode current.
As a result, the anode current of the right half of lamp L2 and the screen voltage of lamp L1 change, which leads to the appearance of a modulated signal at the output of the transmitter. The CLC modulator practically does not require adjustment. It is only necessary to set, using potentiometer R3, the anode current of lamp L1 when silent in the TLF mode equal to 20-25% of the value of the anode current in the TLG mode. If this cannot be achieved, the bias voltage should be increased or the excitation voltage of lamp L1 should be reduced. The CLC modulator has been in use at the radio station for a long time. In all cases, the quality of modulation was assessed positively by correspondents.
Amplitude modulation (AM)- the most common type of modulation. In an AM system, the amplitude of the carrier changes according to changes in the signal or information (Fig. 14.1). In the absence of a signal, the carrier amplitude remains at a constant level, as shown in Fig. 14.1(b). When modulated by a sinusoidal signal, the amplitude of the carrier increases or decreases relative to its unmodulated level according to a sinusoidal law in accordance with the rise or fall of the modulating signal. The greater the amplitude of the modulating signal, the more the amplitude of the carrier changes. An amplitude-modulated carrier (Fig. 14.1(c)) has an envelope that exactly follows the shape of the modulating signal, and during demodulation it is this envelope that is identified as the useful signal.
Modulation depth
The ratio of the amplitude of the modulating signal to the amplitude of the carrier is called the depth or modulation ratio. It determines the measure of change in carrier level during modulation. Modulation depth is always expressed as a percentage and is therefore referred to as "percentage" modulation.
Signal amplitude
Modulation depth = ----------- 100%
Carrier amplitude
(see Fig. 14.1). For example, if the signal amplitude is 1 V and the carrier amplitude is 2 V, then the modulation depth is (1 V)/(2 V) 100% = 50%. This is the modulation depth of the AM carrier shown in Fig. 14.1.
Rice. 14.1. Amplitude modulation (modulation depth 50%);
(a) signal; (b) carrier; (c) modulated carrier.
Overmodulation
In Fig. Figure 14.2(a) shows an AM carrier with 100% modulation depth. Modulation depth exceeding 100% leads to distortion (Fig. 14.2(b)). For this reason, the modulation depth is limited. For example, for BBC radio broadcasts it is limited to 80%.
Rice. 14.2. (a) Modulation 100%; (b) overmodulation.
Side frequencies
It can be shown that an amplitude-modulated carrier consists of three harmonic (sinusoidal) components with constant amplitudes and different frequencies. These three components are: the carrier itself and two sideband signals f1 and f2. Each modulating harmonic signal generates two side frequencies. Let fs be the frequency of the modulating signal and fc be the carrier frequency, then
f1 = fc – fs, f2 = fc + fs,
where f1 and f2 are the so-called lower side and upper side frequencies, respectively. For example, if the carrier frequency is 100 kHz and the signal frequency is 1 kHz, then
Lower side frequency f1 = 100 – 1 = 99 kHz,
Upper side frequency f2 = 100 + 1 = 101 kHz.
An amplitude-modulated carrier, that is, a carrier plus two sideband signals, can be represented as three vertical arrows, each of which corresponds to one harmonic signal (Fig. 14.3). What is shown in this figure is called the frequency spectrum of the signal (in this case, the frequency spectrum of the AM carrier).
Rice. 14.3. AM carrier frequency spectrum. Rice. 14.4. Side stripes.
Side stripes
Information signals almost always have a complex shape and consist of a large number of harmonic signals. Since each harmonic signal produces a pair of side frequencies, a complex non-harmonic signal will produce multiple side frequencies, resulting in two frequency bands on either side of the carrier (Figure 14.4). These are the so-called sidebands. The frequency region between the highest upper sideband frequency f2 and the smallest upper sideband frequency f4 is called the upper sideband (HSB). Similarly, the frequency region between the highest lower sideband frequency f3 and the lowest lower sideband frequency f1 is called the lower sideband (LSB).
These two sidebands are located symmetrically with respect to the carrier, and each of them contains the same information. The carrier does not carry any information. All information is carried by side frequencies.
When modulating with a single harmonic signal, the upper and lower sidebands are assumed to extend from the carrier to the upper and lower sidebands, respectively (Fig. 14.5).
Example 1
A carrier with a frequency of 100 kHz is amplitude modulated with a signal occupying the frequency band 400-3400 Hz. Determine the width of the side stripes.
Solution
The frequency of 3400 Hz, the highest in the signal spectrum, generates two side frequencies (Fig. 14.6):
f1 = 100,000 - 3400 = 96,600 Hz,
f2 = 100,000 + 3400 = 103,400 Hz.
Rice. 14.6.
The frequency of 400 Hz, the lowest in the signal spectrum, gives rise to two more side frequencies:
f3 = 100,000 - 400 == 99,600 Hz,
f4 = 100,000 + 400 = 100,400 Hz.
Upper sideband width (HSB): f2 – f4 = 103400 - 100400 = 3000 Hz.
Low sideband width (LSB): f3 – f1 = 99,600 - 96,600 = 3000 Hz.
In other words, both sidebands have the same width, equal to the difference between the highest and lowest frequencies in the spectrum of the modulating signal: 3400 - 400 = 3000 Hz.
The sidebands for any other frequency in the signal spectrum will be within the upper and lower sidebands.
Bandwidth
Since only side frequencies carry information, for high-quality transmission of this information, the frequency bandwidth occupied on the air by the AM system must be large enough to accommodate all available side frequencies. When modulated by a harmonic signal, two side frequencies arise. Thus, the frequency band extends from the lower sideband frequency f1 to the upper sideband frequency f2 (as shown in Fig. 14.5).
For example, if the modulating harmonic signal has a frequency of 1 kHz, then BBP = NBP = 1 kHz and the bandwidth will be
NBP + VBP = 2 1 kHz = 2 kHz.
In other words, in this case, the bandwidth occupied by the amplitude-modulated carrier is equal to twice the frequency of the modulating signal.
In the case of complex signal transmission, the bandwidth occupied by the AM transmission system is equal to twice the highest frequency in the spectrum of the baseband signal and thus includes all side frequencies.
One- and two-way transmission
Since one sideband contains as much information as the other, transmission can be accomplished using only one sideband without any loss of information. In single-sideband transmission (SSB in communication terminology), one of the sidebands - either the lower or the upper - is suppressed and only the remaining sideband is transmitted. In dual-sideband (DSB) transmission, both sidebands are transmitted.
Single-sideband transmission takes up only half the frequency bandwidth used by dual-sideband transmission, and for this reason it is used in telephony and radio communications. With single-sideband transmission, twice as many information channels can be placed in a given carrier frequency range as with dual-sideband transmission. Because of its simplicity, two-way transmission is used by all AM broadcast systems. Therefore, when talking about AM communications, it usually means dual-lane transmission unless otherwise noted.
Example 2
The carrier is modulated in amplitude by a periodic signal in the form of a meander with a frequency of 100 Hz. Ignoring harmonics above the fifth, set the bandwidth required for a) DSB (double sideband) transmission and b) SSB (single sideband) transmission.
Solution
The signal in the form of a square wave with a frequency of 100 Hz contains the following harmonics:
fundamental harmonic =100 Hz,
3rd order harmonic = 3 100 = 300 Hz,
5th order harmonic = 5 100 = 500 Hz.
We neglect higher order harmonics. Thus, in the cut spectrum of the modulating signal, the maximum frequency fmax = 500 Hz.
Bandwidth for DSB transmission = 2 fmax = 2500 = 1000 Hz.
Bandwidth for SSB transmission = DSB/2 = 1000/2 = 500 Hz.
This video talks about amplitude modulation:
