- Micropower UMZCH on TDA7050
Using the TDA7050 IC you can assemble a simple headphone amplifier. The amplifier circuit on the TDA7050 contains virtually no external elements, is easy to assemble and does not require configuration. The amplifier power supply range is from 1.6 to 6 V (3-4 V recommended). Output power in the stereo version is 2*75 mW and in the bridge version 150 mW. The load resistance in the stereo version of the amplifier […]
- DC-DC converter 5V to 12V on LM2586
The figure shows a circuit of a simple converter based on the LM2586 IC. Main characteristics of the DC-DC integrated converter LM2586: Input voltage from 4 to 40 V Output voltage from 1.23 to 60 V Conversion frequency 75 ... 125 kHz Internal current consumption no more than 11 mA Maximum output current 3 A The circuit contains a minimum set of external elements, IC LM2586 must be installed on […]
- LM2877 - UMZCH 2x4W
The figure shows the circuit of an amplifier assembled on the LM2877 IC. The amplifier has a minimum number of external elements and does not require adjustment after assembly. Main technical characteristics of the amplifier on LM2877: Supply voltage 6 ... 24 V (unipolar) or ±3 ... 12 V (bipolar) Output power 4 ... 4.5 W per channel with a supply voltage of 20 V and a load resistance of 8 […]
- DC-DC converter 5V to 12V
The converter circuit is based on the LT1070 IC. The circuit contains a minimal set of external elements and is easy to assemble. The output voltage is adjusted by selecting resistances R1 and R2. Choke L1 is recommended according to the datasheet PE-92113, but you can use another one with a rated current of 1A, with an inductance of 150 μH. Source - lt1070ck.pdf
- Power amplifier on STK082
The integrated circuit STK082 manufactured by Sanyo is made in a SIP10 package and is a low-frequency power amplifier in a hybrid design. The STK082 IC is intended for use in tape recorders, electrophones, television and radio receivers, and other high-end audio equipment with bipolar power supply. The microcircuits do not have output protection against short circuits in the load. Main technical characteristics: Maximum supply voltage ± 43 […]
- KA2211 - two-channel amplifier 5.8 W
The figure shows the circuit of a simple amplifier with an output power of 5.8 W per channel, the amplifier is based on the KA2211 IC (Samsung). Characteristics of IC KA2211: Maximum supply voltage 25 V Nominal supply voltage 13.2 V Recommended supply voltage range 10...18 V Output power 5.8 W per SOI channel at Rn=4 Ohm at maximum power 5.8 W... 10% [... ]
- Electric rotation control engine using IC MAX4295
The MAX4295 is a Class D audio amplifier, which offers power efficiency benefits when running on battery power, making the MAX4295 ideal for controlling the speed and direction of rotation of miniature DC motors. Instead of the input audio signal, the modified AF amplifier circuit is supplied with a constant voltage from potentiometer R1. The potentiometer impedance corresponds to the maximum engine speed, the middle […]
- TDA2002 - ULF 10 W
The figure shows the circuit of a simple class AB amplifier using the TDA2002 IC. The amplifier based on the TDA2002 IC has a minimal set of external elements and does not require configuration after assembly. TDA2002 has short circuit protection and thermal protection. With a supply voltage of 16 V and a load of 2 ohms, the amplifier can achieve up to 10 W of output power. The supply voltage can be within […]
- L5970D pulse DC-DC converter
IC L5970D is a switching DC-DC converter, used in buck, boost and inverting converters using a minimum number of external elements. Main features of the converter: input voltage from 4.4V to 36V; low current consumption at no load; internal output current limiting circuit; output current up to 1A; shutdown function when the microcircuit overheats; output voltage is regulated by an external divider from 1.2V to […]
- Switching voltage regulator L4971
IC L4971 is a switching step-down voltage stabilizer, with an adjustable output voltage from 3.3 V to 50 V, with an input voltage from 8 V to 55 V. The maximum load current is up to 1.5A. The internal structure of the microcircuit contains a 3.3V reference voltage source, a function for changing the operating switching frequency up to 300 kHz, a powerful power switch represented by an n-channel field-effect transistor, […]
To set up various RF devices (receivers, transmitters...), it is not possible to measure the signal level with a conventional voltmeter. Therefore, here it is necessary to use an HF voltmeter.
One of these is the circuit proposed below for a simple RF millivoltmeter on two transistors.
Schematic diagram of an RF millivoltmeter
The DC millivoltmeter circuit is built on transistors VI.1 and VI.2 and a high-frequency voltage rectifier on diode V2.
The use of an integrated assembly of transistors allows us to minimize the imbalance of the millivoltmeter's DC amplifier due to changes in ambient temperature.
As V2, it is advisable to use a silicon diode designed for mixing signals or detecting them in the decimeter wavelength range.
You can also use some of the pulse diodes designed for high-speed switches here. Temperature compensation of the operating mode of diode V2 is provided by silicon diode V3, forward biased.
The operating point of the rectifier diode V2 is set by trimming resistor R9 according to its maximum sensitivity. The millivoltmeter is balanced (in the absence of RF voltage at the input) using a trimming resistor R 7.
Calibrate the device using trimming resistor R8.
The millivoltmeter scale is nonlinear and is made individually for each device.
Instead of an integral pair of transistors, you can also use individual transistors, selected to have the same gain.
All components of the device are made on a printed circuit board.
In an HF millivoltmeter, you can use transistor assemblies K125NT1 or K166NT1A (and one of the transistors in the assembly will successfully serve as a thermal stabilizing diode) or the like, and also (as written above) you can select a pair of transistors from the KT312, KT315, etc. series (according to static current transfer coefficients at a fixed value of the collector current and base-emitter voltage at a fixed value of the base current).
Source: Designs of Soviet and Czechoslovak radio amateurs: Sat. articles. 1987. (MRB No. 1113)
P O P U L A R N O E:
You can make a real birdhouse so that starlings can live in it.
Or you can make a small toy birdhouse from ordinary matches.
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A simple heterodyne resonance indicator.
With the L2 coil short-circuited, the GIR allows you to determine the resonant frequency from 6 MHz
up to 30 MHz. With the L2 coil connected, the frequency measurement range is from 2.5 MHz to 10 MHz.
The resonant frequency is determined by rotating the rotor C1 and observing on the oscilloscope screen
signal change.
High frequency signal generator.
The high frequency signal generator is designed for testing and setting up various high frequency devices. The range of generated frequencies 2 ..80 MHz is divided into five subranges:
I - 2-5 MHz
II - 5-15 MHz
III - 15 - 30 MHz
IV - 30 - 45 MHz
V - 45 - 80 MHz
The maximum amplitude of the output signal at a load of 100 Ohms is about 0.6 V. The generator provides smooth adjustment of the amplitude of the output signal, as well as the ability
amplitude and frequency modulation of the output signal from an external source. The generator is powered from an external DC voltage source of 9... 10 V.
The schematic diagram of the generator is shown in the figure. It consists of an RF master oscillator, made on transistor V3, and an output amplifier on transistor V4. The generator is made according to an inductive three-point circuit. The desired subrange is selected with switch S1, and the generator is rebuilt with variable capacitor C7. From the drain of transistor V3, the RF voltage is supplied to the first gate
field effect transistor V4. In FM mode, low-frequency voltage is applied to the second gate of this transistor.
Frequency modulation is carried out using a varicap VI, which is supplied with low-frequency voltage in FM mode. At the generator output, the RF voltage is smoothly regulated by resistor R7.
The generator is assembled in a housing made of one-sided foil fiberglass laminate with a thickness of 1.5 mm, dimensions 130X90X48 mm. Installed on the front panel of the generator
switches S1 and S2 of type P2K, resistor R7 of type PTPZ-12, variable capacitor S7 of type KPE-2V from the Alpinist-405 radio receiver, which uses both sections.
Coil L1 is wound on a ferrite magnetic core M1000NM (K10X6X X4,b) and contains (7+20) turns of PELSHO 0.35 wire. Coils L2 and L3 are wound on frames with a diameter of 8 and a length of 25 mm with carbonyl trimmed cores with a diameter of 6 and a length of 10 mm. Coil L2 consists of 5 + 15 turns of PELSHO 0.35 wire, L3 - of 3 + 8 turns. Coils L4 and L5 are frameless
with a diameter of 9 mm, they are wound with PEV-2, 1.0 wire. Coil L4 contains 2 + 4 turns, and L5 - 1 + 3 turns.
Setting up the generator begins with checking the installation. Then the supply voltage is applied and using an RF voltmeter, the presence of generation is checked on all subbands. Borders
ranges are clarified using a frequency meter, and if necessary, capacitors C1-C4 (C6) are selected, the cores of coils L2, L3 are adjusted and the distance between the turns of coils L4 and L5 is changed.
Multimeter-HF millivoltmeter.
Nowadays, the most affordable and most common radio amateur device is the M83x series digital multimeter.
The device is intended for general measurements and therefore has no specialized functions. Meanwhile, if you are involved in radio receiving or transmitting equipment, you need to measure
small RF voltages (local oscillator, amplifier stage output, etc.), adjust the circuit. To do this, the multimeter must be supplemented with a simple remote measuring head containing
high-frequency detector using germanium diodes. The input capacitance of the RF head is less than 3 pF, which allows it to be connected directly to the local oscillator or cascade circuit. You can use diodes D9, GD507 or D18; diodes D18 gave the greatest sensitivity (12 mV). The RF head is assembled in a shielded housing on which terminals are located for connecting the probe or conductors to the circuit being measured. Communication with a multimeter using a shielded television cable RK-75.
Measuring small capacitances with a multimeter
Many radio amateurs use multimeters in their laboratories, some of which can also measure capacitances of capacitors. But as practice shows, these devices cannot measure capacitance up to 50 pF, and up to 100 pF there is a large error. This attachment is designed to allow you to measure small containers. Having connected the set-top box to the multimeter, you need to set the value on the indicator to 100pf, adjusting C2. Now, when you connect a 5 pf capacitor, the device will show 105. All that remains is to subtract the number 100
Hidden Wiring Finder
A relatively simple finder made with three transistors will help determine the location of hidden electrical wiring in the walls of a room (Fig. 1). A multivibrator is assembled on two bipolar transistors (VT1, VT3), and an electronic switch is assembled on a field-effect transistor (VT2).
The principle of operation of the finder is based on the fact that an electric field is formed around an electric wire and is captured by the finder. If the SB1 switch button is pressed, but there is no electric field in the area of the WA1 antenna probe or the finder is far from the network wires, the VT2 transistor is open, the multivibrator does not work, and the HL1 LED is off. It is enough to bring the antenna probe connected to the field gate circuit closer
transistor, to a current-carrying conductor or simply to a network cable, transistor VT2 will close, the shunting of the base circuit of transistor VT3 will stop and the multivibrator will come into effect. The LED will start flashing. By moving the antenna probe near the wall, it is easy to trace the route of network wires in it.
The device allows you to find the location of the phase wire break. To do this, you need to plug in a load, such as a table lamp, into the outlet and move the antenna probe of the device along the wiring. In the place where the LED stops blinking, you need to look for a malfunction.
The field-effect transistor can be any other from the series indicated in the diagram, and bipolar transistors can be any from the KT312, KT315 series. All
resistors - MLT-0.125, oxide capacitors - K50-16 or other small ones, LED - any of the AL307 series, power source - Krona battery or rechargeable battery with a voltage of 6...9 V, push-button switch SB1 - KM-1 or similar. Some of the device parts are mounted on a board (Fig. 2) made of one-sided foil fiberglass. The finder body can be a plastic case (Fig. 3)
for storing school counting sticks. The board is mounted in its upper compartment, and the battery is located in the lower compartment. A switch and LED are attached to the side wall of the upper compartment, and an antenna probe is attached to the top wall. It is a conical
A plastic cap containing a threaded metal rod inside. The rod is attached to the body with nuts; from inside the body, a metal petal is placed on the rod, which is connected with a flexible mounting conductor to resistor R1 on the board. The antenna probe can be of a different design, for example, in the form of a loop from a piece of thick (5 mm) high-voltage wire used in a TV. Length
a segment of 80...100 mm, its ends are passed through the holes in the upper compartment of the case and soldered to the corresponding point on the board. The desired oscillation frequency of the multivibrator, and therefore the frequency of LED flashes, can be set by selecting resistors RЗ, R5 or capacitors C1, C2. To do this, you need to temporarily disconnect the source output from resistors RЗ and R4.
left transistor and close the switch contacts. If, when searching for a broken phase wire, the sensitivity of the device turns out to be excessive, it can be easily reduced by reducing the length of the antenna probe or disconnecting the conductor connecting the probe to the printed circuit board. The finder can also be assembled according to a slightly different scheme (Fig. 4) using bipolar transistors of different structures - a generator is made on them. The field-effect transistor (VT2) still controls the operation of the generator when the antenna probe WA1 enters the electric field of the network wire.
Transistor VT1 can be a series
KT209 (with indexes A-E) or KT361,
VT2 - any of the KP103 series, VT3 - any of the KT315, KT503, KT3102 series. Resistor R1 can have a resistance of 150...560 Ohms, R2 - 50 kOhm...1.2 MOhm, R3 and R4 with a deviation from the values indicated in the diagram by ±15%, capacitor C1 - with a capacity of 5...20 μF. The printed circuit board for this version of the finder is smaller in size (Fig. 5), but the design is almost the same as the previous version.
Any of the described finders can be used to monitor the operation of the car ignition system. By bringing the antenna probe of the finder to the high-voltage wires, by blinking the LED, they determine circuits that do not receive high voltage, or find a faulty spark plug.
Journal "Radio", 1991, No. 8, p. 76
A not quite ordinary GIR diagram is shown in the figure. The difference is in the remote loop of communication. Loop L1 is made of copper wire with a diameter of 1.8 mm, the diameter of the loop is about 18 mm, the length of its leads is 50 mm. The loop is inserted into the sockets located at the end of the body. L2 is wound on a standard ribbed body and contains 37 turns of wire with a diameter of 0.6 mm with taps from the 15, 23, 29 and 32 turns Range - from 5.5 to 60 MHz
Simple capacitance meter
The capacitance meter allows you to measure the capacitance of capacitors from 0.5 to 10000pF.
A multivibrator is assembled on TTL logic elements D1.1 D1.2, the frequency of which depends on the resistance of the resistor connected between input D1.1 and output D1.2. For each measurement limit, a certain frequency is set using S1, one section of which switches resistors R1-R4, and the other capacitors C1-C4.
Pulses from the output of the multivibrator are supplied to the power amplifier D1.3 D1.4 and then through the reactance of the measured capacitor Cx to a simple AC voltmeter on the microammeter P1.
The readings of the device depend on the ratio of the active resistance of the device frame and R6, and the reactance Cx. In this case, Cx depends on the capacitance (the larger, the lower the resistance).
The device is calibrated at each limit using trimming resistors R1-R4, measuring capacitors with known capacities. The sensitivity of the device indicator can be set by selecting the resistance of resistor R6.
Literature RK2000-05
Simple function generator
In an amateur radio laboratory, a function generator must be a mandatory attribute. We bring to your attention a functional generator capable of generating sine, square, and triangular signals with high stability and accuracy. If desired, the output signal can be modulated.
The frequency range is divided into four sub-bands:
1. 1Hz-100Hz,
2. 100Hz-20kHz,
3. 20KHz-1MHz,
4. 150KHz-2 MHz.
The exact frequency can be set using potentiometers P2 (coarse) and P3 (fine)
Function generator regulators and switches:
P2 - coarse frequency setting
P3 - frequency fine tuning
P1 - Signal amplitude (0 - 3V with 9V supply)
SW1 - range switch
SW2 - Sine/Triangle signal
SW3 - Sine (triangular) / square wave
To control the frequency of the generator, the signal can be removed directly from pin 11.
Options:
Sine wave:
Distortion: less than 1% (1 kHz)
Flatness: +0.05 dB 1 Hz - 100 kHz
Square wave:
Amplitude: 8V (no load) with 9V supply
Rise time: less than 50 ns (at 1 kHz)
Fall Time: Less than 30ns (at 1KHz)
Unbalance: less than 5%(1 kHz)
Triangle signal:
Amplitude: 0 - 3V with 9V supply
Nonlinearity: less than 1% (up to 100 kHz)
Network overvoltage protection
The ratio of capacitances C1 and the composite capacitances C2 and C3 affects the output voltage. The rectifier power is enough for parallel connection of 2-3 relays of type RP21 (24V)
Generator for 174x11
The figure shows a generator based on the K174XA11 microcircuit, the frequency of which is controlled by voltage. By changing capacitance C1 from 560 to 4700 pF, a wide range of frequencies can be obtained, while the frequency is adjusted by changing resistance R4. For example, the author found out that, with C1 = 560pF, the generator frequency can be changed using R4 from 600Hz to 200kHz, and with a capacitance of C1 of 4700pF, from 200Hz to 60kHz.
The output signal is taken from pin 3 of the microcircuit with an output voltage of 12V; the author recommends feeding the signal from the output of the microcircuit through a current-limiting resistor with a resistance of 300 Ohms.
Inductance meter
The proposed device allows you to measure the inductance of coils at three measurement limits - 30, 300 and 3000 μH with an accuracy of no worse than 2% of the scale value. The readings are not affected by the coil’s own capacitance and its ohmic resistance.
A generator of rectangular pulses is assembled on the 2I-NOT elements of the DDI microcircuit, the repetition frequency of which is determined by the capacitance of the capacitor C1, C2 or S3, depending on the measurement limit switched on by switch SA1. These pulses, through one of the capacitors C4, C5 or C6 and the diode VD2, are supplied to the measured coil Lx, which is connected to terminals XS1 and XS2.
After the cessation of the next pulse during a pause, due to the accumulated energy of the magnetic field, the current through the coil continues to flow in the same direction through the diode VD3, its measurement is carried out by a separate current amplifier assembled on transistors T1, T2 and a pointer device PA1. Capacitor C7 smoothes out current ripples. Diode VD1 serves to bind the level of pulses supplied to the coil.
When setting up the device, it is necessary to use three reference coils with inductances of 30, 300 and 3000 μH, which are alternately connected instead of L1, and the corresponding variable resistor R1, R2 or R3 sets the device pointer to the maximum scale division. During operation of the meter, it is enough to calibrate with variable resistor R4 at the measurement limit of 300 μH, using coil L1 and turning on switch SB1. The microcircuit is powered from any source with a voltage of 4.5 - 5 V.
The current consumption of each battery is 6 mA. You don’t have to assemble the current amplifier for the milliammeter, but connect a microammeter with a scale of 50 μA and an internal resistance of 2000 Ohms in parallel with capacitor C7. Inductance L1 can be composite, but then the individual coils should be positioned mutually perpendicular or as far apart as possible. For ease of installation, all connecting wires are equipped with plugs, and the corresponding sockets are installed on the boards.
Simple radioactivity indicator
Loterodyne resonance indicator
G.Gvozditsky
The schematic diagram of the proposed GIR is shown in Fig. 1. Its local oscillator is made on a field-effect transistor VT1, connected according to a circuit with a common source. Resistor R5 limits the drain current of the field-effect transistor. Choke L2 is an element decoupling the local oscillator from the power source at high frequency.
Diode VD1, connected to the gate and source terminals of the transistor, improves the shape of the generated voltage, bringing it closer to a sinusoidal one. Without a diode, the positive half-wave of the drain current will become distorted due to the increase in the transistor gain with increasing gate voltage, which inevitably leads to the appearance of even harmonics in the spectrum of the local oscillator signal
Through capacitor C5, radio frequency voltage is supplied to the input of a high-frequency voltmeter-indicator, consisting of a detector whose diodes VD2 and VD4 are connected according to a voltage doubling circuit, which increases the sensitivity of the detector and the stability of the DC amplifier on transistor VT2 with microammeter PA1 in the collector purpose. Diode VD3 stabilizes the reference voltage on diodes VD2, VD4. Using a variable resistor R3 combined with the power switch SA1, set the microammeter arrow PA1 to its original position at the far right scale mark
If in some parts of the range it is necessary to increase the accuracy of the scale, then connect a mica capacitor of constant capacity in parallel with the coil.
A variant of coils made on frames from laboratory test tubes for blood collection are shown in the photo (Fig. 2) and are selected by a radio amateur for the desired range
The inductance of the loop coil and the capacitance of the loop, taking into account the additional capacitor, can be calculated using the formula
LC=25330/f²
where C is in picofarads, L is in microhenry, f is in megahertz.
When determining the resonant frequency of the circuit under study, bring the GIR coil as close as possible to it and slowly rotating the knob of the KPI block, monitor the indicator readings. As soon as its arrow swings to the left, mark the corresponding position of the KPI handle. With further rotation of the adjustment knob, the instrument arrow returns to its original position. That mark on the scale where the maximum *dip* of the arrow is observed will precisely correspond to the resonant frequency of the circuit under study
The described GIR does not have an additional supply voltage stabilizer, so when working with it it is recommended to use a source with the same DC voltage value - optimally a mains power supply with a stabilized output voltage.
It is impractical to make one common scale for all ranges due to the complexity of such work. Moreover, the accuracy of the resulting scale with different tuning densities of the applied contours will complicate the use of the device.
L1 coils are impregnated with epoxy glue or HH88. For HF ranges, it is advisable to wind them with silver-plated copper wire with a diameter of 1.0 mm.
Structurally, each contour coil is placed on the base of the common SG-3 connector. It is glued into the reel frame.
Simplified version of GIR
It differs from the GIR G. Gvozditsky in what has already been written about in the article - the presence of a middle terminal of a replaceable coil L1, a Tesla variable capacitor with a solid dielectric is used, there is no diode that forms a sinusoidal signal. There is no RF voltage doubler rectifier and UPT, which reduces the sensitivity of the device.
On the positive side, it should be noted the presence of “stretching” switchable capacitors C1, C2 and a simple vernier, combined with two switching scales that can be graduated with a pencil; the power is turned on with a button only at the time of measurements, which saves the battery.
To power the Geiger counter B1, a voltage of 400V is required, this voltage is generated by a source on a blocking generator on transistor VT1. Pulses from the step-up winding T1 are rectified by a rectifier on VD3C2. The voltage at C2 is supplied to B1, the load of which is resistor R3. When an ionizing particle passes through B1, a short current pulse appears in it. This pulse is amplified by a pulse shaper amplifier on VT2VT3. As a result, a longer and stronger current pulse flows through F1-VD1 - the LED flashes, and a click is heard in the F1 capsule.
The Geiger counter can be replaced with any similar one, F1 with any electromagnetic or dynamic resistance of 50 Ohms.
T1 is wound on a ferrite ring with an outer diameter of 20 mm, the primary winding contains 6+6 turns of PEV 0.2 wire, the secondary winding contains 2500 turns of PEV 0.06 wire. Between the windings you need to lay insulating material made of varnished fabric. The secondary winding is wound first, and the secondary surface is evenly wound on it.
Capacitance measuring device
The device has six subranges, the upper limits of which are 10pF, 100pF, 1000pF, 0.01 µF, 0.1 µF and 1 µF, respectively. The capacitance is read using the linear scale of a microammeter.
The operating principle of the device is based on measuring alternating current flowing through the capacitor under study. A rectangular pulse generator is assembled on the operational amplifier DA1. The repetition rate of these pulses depends on the capacitance of one of the capacitors C1-C6 and the position of the trimmer resistor R5. Depending on the subband, it varies from 100Hz to 200kHz. Using trimming resistor R1 we set a symmetrical oscillation shape (square wave) at the generator output.
Diodes D3-D6, trimming resistors R7-R11 and microammeter PA1 form an alternating current meter. In order for the measurement error not to exceed 10% in the first subrange (capacitance up to 10 pF), the internal resistance of the microammeter should be no more than 3 kOhm. On the remaining subranges, trimming resistors R7-R11 are connected in parallel to PA1.
The required measurement subrange is set with switch SA1. With one group of contacts it switches frequency-setting capacitors C1-C6 in the generator, the other - trimming resistors in the indicator. To power the device, a stabilized bipolar source with a voltage of 8 to 15V is required. The ratings of frequency-setting capacitors C1-C6 may differ by 20%, but the capacitors themselves must have sufficiently high temperature and time stability.
Setting up the device is carried out in the following sequence. First, in the first subband, symmetrical oscillations are achieved with resistor R1. The resistor R5 slider should be in the middle position. Then, having connected a 10pF reference capacitor to the “Cx” terminals, use trimming resistor R5 to set the microammeter needle to the division corresponding to the capacitance of the reference capacitor (when using a 100-μA device, to the final scale division).
Set-top box diagram
An attachment to a frequency meter for determining the circuit tuning frequency and its preliminary tuning. The set-top box is operational in the range of 400 kHz-30 MHz.T1 and T2 can be KP307, BF 245
LY2BOK
V. Kostychev, UN8CB.
Petropavlovsk.
This simple device allows you to measure the effective (rms) value of voltage and power of HF oscillations, both sinusoidal and modulated, and also, with the improvement of the device, peak power. The basis of this device is a simple diode high-frequency voltmeter, which are used in SWR meters, as well as in imported devices SX-100, SX-200. Such a similar diode voltmeter is also used in the BB-10 device, the diode of which is supplied with RF voltage through a current transformer (Fig. 1).
(Blue parts are installed additionally for the peak indicator when the device is improved). When the device operates in the mode of an absorbing power meter, a load resistor Rн is connected to the “ANT” connector using switch S1. When operating in the transmitted power meter mode, Rн is disconnected and the antenna is connected. Switch S2 sets the measurement limit to 100 W or 500 W.
For current transformer T1, a ring 1000NN-2000NN with a diameter of 12-16 mm is used, winding with PEL 0.5 wire; 4 - 5 turns. A fairly thick insulated wire is passed through the ring of transformer T1, connecting the “ANT” and “PER” connectors, located about 5 cm from each other on the back wall of the device. Microammeter RA - type M2001 with a total deviation current of 100 μA. The load resistor consists of 30 MLT-1.5 k resistors, 2 W power (total resistance 50 Ohms). Total power Rн - 60 W. The resistors are soldered between two boards made of foil fiberglass. (Fig.2).
Mounting of device parts mounted, using support points, in a housing of a suitable size
The instrument scale is graduated in volts and watts. To do this, an RF voltmeter (type V7-15) is connected in parallel with Rн. The transmitter is connected to the “PER” connector, switch S2 is in the 100 W position. The carrier transmission mode is turned on at a frequency of 14 MHz, gradually increasing the output power to set the RF voltage at Rn equal to 70.7 V, which will correspond to a power of 100 W. Resistor R3 sets the microammeter needle to the last scale mark - 100 µA. By reducing the output power of the transmitter, we determine the microammeter readings for other power values, based on the expression: Reff = (Ueff)2/ Rn. The result is entered into calibration table 1.
Table 1.
To calibrate the scale at the limit of 500 W, switch S2 to the 500 W position, set the transmitter power to 100 W and use resistor R4 to fix the microammeter needle at 44.5 µA. Then, reducing the transmitter power, and then increasing it, calibrate the rest of the scale for this limit. This table can be used later when working with the device. You can stick it on the top cover.
When working with the device, you need to remember that Rн is designed for a power of 60 W, therefore, at high powers, the measurement time should not be long, with interruptions.
The operating instructions for the SX-100, SX-200 devices state that these devices are not capable of showing 100% of peak power, but only 70% - 90%. Also, a significant drawback of the SX-100, SX-200 devices is the lack of more or less long-term recording of readings when measuring regular conversational peak power, which makes it difficult to count. In the BB-10 device, these shortcomings are eliminated if you use a peak indicator in the form of an additional attachment to the BB-10 on an operational amplifier, for example, which is offered by DJ7AW (Radio No. 7, 2011, p. 63). This peak indicator was tested and showed good results. Fig.3.
To connect it in the diagram in Fig. 1, it is necessary to make some changes. Switch S3 is switched into the gap between points “a-a” and connected, as shown in the diagram in Fig. 1 in blue. In position 1 of switch S3, effective power is measured, and in position 2, peak power is measured. In the peak power measurement mode, the DC voltage from the voltmeter-wattmeter rectifier is supplied through the operational amplifier DA1.1 to the peak detector VD1, R4, C2. The time constant of this detector (about 6.8 s) is quite sufficient to record normal conversational peak power. The repeater on the operational amplifier DA1.2 eliminates shunting of the load of the peak detector, which allows increasing the time of recording the readings of the measuring device. The peak indicator is assembled on a plate measuring 45x38 mm, mounted on the spots, Fig. 4.
The blue color indicates a piece of insulated wire (instead of a track) passed under the socket for the microcircuit soldered to the contact pads. Capacitor C2 is non-polar. The board is connected to points A and B of the circuit in Fig. 1. One bad thing is that to power this circuit you need a 12V power source.
The magazine does not provide a method for setting and calibrating this peak indicator. I did this based on the considerations that in linear mode, the effective power and the peak power of the sine wave (carrier) are equal, and the peak power of the modulated signal when pronouncing a moderate sound “a-a-a” in front of the microphone is approximately equal to the effective power of the carrier. The voltage level supplied from the detector to the op-amp DA1 must be such that it does not enter saturation mode. To do this, the R1 engine was installed at approximately 1/3 of its resistance from the ground. Calibration when measuring the peak power of the modulated signal (S3 in position 2) is carried out by resistor R6 (with a transmitter output power of about 100 W) in the long “a-a-a” mode, by which the microammeter readings are set to the same as when measuring the effective power in carrier mode (S3 in position 1). Then, when measuring the peak power of modulated oscillations, a more or less real result should be obtained. For the BB-10 device this figure is about 95%.
High accuracy of HF voltage measurements (up to the third or fourth digit) is, in fact, not needed in amateur radio practice. The quality component is more important (the presence of a sufficiently high level signal - the more, the better). Typically, when measuring an RF signal at the output of a local oscillator (oscillator), this value does not exceed 1.5 - 2 volts, and the circuit itself is adjusted to resonance according to the maximum RF voltage value. When adjusted in the IF paths, the signal increases step by step from units to hundreds of millivolts.
When setting up local oscillators and IF paths, tube voltmeters (such as VK 7-9, V7-15, etc.) with measurement ranges of 1 - 3 V are still often used. High input resistance and low input capacitance in such devices are the determining factor, and the error is up to 5-10% and is determined by the accuracy of the dial measuring head used. Measurements of the same parameters can be carried out using homemade pointer instruments, the circuits of which are made on microcircuits with field-effect transistors at the input. For example, in B. Stepanov’s HF millivoltmeter (2), the input capacitance is only 3 pF, the resistance in various subranges (from 3 mV to 1000 mV) even in the worst case does not exceed 100 kOhm with an error of +/- 10% (determined by the head used and instrumentation error for calibration). In this case, the measured RF voltage is with the upper limit of the frequency range of 30 MHz without an obvious frequency error, which is quite acceptable in amateur radio practice.
In terms of circuit design, the proposed device is very simple, and the minimum components used can be found “in the box” of almost every radio amateur. Actually, there is nothing new in the scheme. The use of op-amps for such purposes is described in detail in the amateur radio literature of the 80-90s (1, 4). The widely used microcircuit K544UD2A (or UD2B, UD1A, B) with field-effect transistors at the input (and therefore with high input resistance) was used. You can use any operational amplifiers of other series with field switches at the input and in a typical connection, for example, K140UD8A. The technical characteristics of the millivoltmeter-voltmeter correspond to those given above, since the basis of the device was B. Stepanov’s circuit (2).
In voltmeter mode, the op-amp gain is 1 (100% OOS) and the voltage is measured with a microammeter up to 100 μA with additional resistances (R12 - R17). They, in fact, determine the subranges of the device in voltmeter mode. When the OOS decreases (switch S2 turns on resistors R6 - R8) Kus. increases, and accordingly the sensitivity of the operational amplifier increases, which allows it to be used in millivoltmeter mode.
A feature of the proposed development is the ability to operate the device in two modes - a direct current voltmeter with limits from 0.1 to 1000 V, and a millivoltmeter with upper limits of subranges of 12.5, 25, 50 mV. In this case, the same divider (X1, X100) is used in two modes, so that, for example, in the 25 mV subrange (0.025 V) using the X100 multiplier, a voltage of 2.5 V can be measured. To switch subranges of the device, one multi-position two-board switch is used.
Using an external RF probe on a GD507A germanium diode, you can measure RF voltage in the same subranges with a frequency of up to 30 MHz.
Diodes VD1, VD2 protect the pointer measuring device from overloads during operation.
Another feature of protecting a microammeter during transient processes that occur when turning the device on and off, when the arrow of the device goes off scale and may even bend, is the use of a relay to turn off the microammeter and short circuit the output of the op-amp to the load resistor (relays P1, C7 and R11). In this case (when the device is turned on), charging C7 requires a fraction of a second, so the relay operates with a delay and the microammeter is connected to the output of the op-amp a fraction of a second later. When the device is turned off, C7 is discharged through the indicator lamp very quickly, the relay is de-energized and breaks the microammeter connection circuit before the op-amp power supply circuits are completely de-energized. The protection of the op-amp itself is carried out by switching on the inputs R9 and C1. Capacitors C2, C3 are blocking and prevent excitation of the op-amp.
Balancing of the device (“setting 0”) is carried out by a variable resistor R10 in the 0.1 V subrange (it is also possible in more sensitive subranges, but when the remote probe is turned on, the influence of hands increases). Capacitors of the K73-xx type are desirable, but if they are not available, you can also take ceramic ones 47 - 68N. The remote probe probe uses a KSO capacitor for an operating voltage of at least 1000V.
Setting up the millivoltmeter-voltmeter is carried out in the following sequence. First, set up the voltage divider. Operating mode - voltmeter. Trimmer resistor R16 (10V subrange) is set to maximum resistance. At resistance R9, monitoring with an exemplary digital voltmeter, set the voltage from a stabilized power source of 10 V (position S1 - X1, S3 - 10 V). Then in position S1 - X100, using trimming resistors R1 and R4, use a standard voltmeter to set 0.1V. In this case, in position S3 - 0.1V, the microammeter needle should be set to the last mark of the instrument scale. The ratio is 100/1 (the voltage across the resistor R9 - X1 is 10V to X100 - 0.1V, when the position of the needle of the device being adjusted is at the last scale mark in the S3 sub-range - 0.1V) is checked and adjusted several times. In this case, a mandatory condition: when switching S1, the reference voltage of 10V cannot be changed.
Further. In the DC voltage measurement mode, in the position of the divider switch S1 - X1 and the subrange switch S3 - 10V, the variable resistor R16 sets the microammeter needle to the last division. The result (at 10 V at the input) should be the same readings of the device on the subrange 0.1V - X100 and the subrange 10V - X1.
The method for setting the voltmeter in the 0.3V, 1V, 3V and 10V subranges is the same. In this case, the positions of the resistor motors R1, R4 in the divider cannot be changed.
Operating mode - millivoltmeter. At the entrance 5th century. In position S3 - 50 mV, divider S1 - X100 with resistor R8 set the arrow to the last scale division. We check the voltmeter readings: in the 10V X1 or 0.1V X100 subrange, the needle should be in the middle of the scale - 5V.
The adjustment method for the 12.5mV and 25mV subranges is the same as for the 50mV subrange. The input is supplied with 1.25V and 2.5V respectively at X 100. The readings are checked in voltmeter mode X100 - 0.1V, X1 - 3V, X1 - 10V. It should be noted that when the microammeter needle is in the left sector of the instrument scale, the measurement error increases.
The peculiarity of this method of calibrating the device: it does not require a standard power source of 12 - 100 mV and a voltmeter with a lower measurement limit of less than 0.1 V.
When calibrating the device in the RF voltage measurement mode with a remote probe for the 12.5, 25, 50 mV subranges (if necessary), you can build correction graphs or tables.
The device is mounted mounted in a metal case. Its dimensions depend on the size of the measuring head used and the power supply transformer. In the above circuit, a bipolar power supply unit operates, assembled on a transformer from an imported tape recorder (primary winding at 110V). The stabilizer is best assembled on MS 7812 and 7912 (or two LM317), but it can be simpler - parametric, on two zener diodes. The design of the remote RF probe and the features of working with it are described in detail in (2, 3).
Used Books:
1. B. Stepanov. Measurement of low RF voltages. J. "Radio", No. 7, 12 - 1980, p.55, p.28.
2. B. Stepanov. High frequency millivoltmeter. Journal "Radio", No. 8 - 1984, p.57.
3. B. Stepanov. RF head for digital voltmeter. Journal "Radio", No. 8, 2006, p.58.
4. M. Dorofeev. Volt-ohmmeter on op-amp. Journal "Radio", No. 12, 1983, p. 30.
