Encyclopedia of radio electronics and electrical engineering / Civil radio communications

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CHANNEL SIGNAL LED

The radio station is supplied with two light-emitting diode indicators: "reception" - "RX" and "transmission" - "TX". The green "RX" LED is permanently on while the station is on. Together with it, the digital indicator of the channel is also on, i.e. they seem to duplicate each other. This allows you to "load" the "RX" LED with additional functions. As one option, it can be used to indicate the presence of a correspondent signal on the channel. In this case, the "RX" LED will only light up when the input signal exceeds the pre-set level.

The scheme of such refinement is shown in Fig. 1. The PCB track that goes to the "RX" LED is cut near the junction of the main PCB and the indication board. A transistor is installed at the site of the cut VT1. The base of transistor VT1 is connected through resistor R1 to pin 1 of IC2. This microcircuit performs the function of a threshold noise suppressor. If the input signal level is below the set threshold, then the output of the IC2 chip will be no more than 1 V. The transistor VT1 is closed, and the LD2 LED is off. When the input signal exceeds the threshold, a voltage of several volts will appear at the output of the microcircuit, the transistor will open and the LED will glow. When switching to the "TX" mode, the transistor supply voltage will be turned off and the LED will turn off.

Transistor VT1 - any low-power low-frequency or medium-frequency one with a base current transfer coefficient of at least 50.

S-METER AND TRANSMITTER OUTPUT POWER INDICATOR

Adding a radio station with such an indicator will allow you to evaluate the signal strength of the correspondent and control the power of your own transmitter. All antenna malfunctions (open, short, significant change in SWR) affect the output signal level. Visual power control will allow you to monitor the health of the antenna economy.

The pointer S-meter in the ALAN-100+ radio station can be connected either to the AM output of the detector, or to the output of the transistor detector of the noise reduction system. In all cases, the S-meter should not adversely affect the performance of these nodes.

A variant of the device connected to the outputs of the AM detector is shown in fig. 2. The buffer stage on the field-effect transistor VT1 provides a large input resistance and does not shunt the detector. Filter R1 C1 suppresses the variable component of the audio signal and passes the constant.

Resistor R5 set the arrow of the device to zero division of the scale, and resistor R3 adjust the sensitivity.

In the absence of an input signal, the voltage at the terminals of the PA1 microammeter is the same and no current flows through PA1. When a signal appears, the negative polarity voltage increases at the output of the detector. The voltage at the source of the transistor VT1 decreases, and a constant current flows through the microammeter PA1, the value of which is proportional to the level of the input signal. Diodes VD1 and VD2 are closed.

In the "TX" mode, the high-frequency voltage from the output of the transmitter is supplied through the capacitive divider C2' C3' C4' to the diode rectifier VD1' VD2'. The rectified voltage causes current to flow through the circuit R6' PA1' R3' R2'. This current is proportional to the voltage at the output of the transmitter. Any malfunctions in the antenna economy will be reflected in the indicator readings. In the transmission mode, power is not supplied to the drain of the transistor VT1'.

All parts of the device, except for the pointer device, can be conveniently placed on two printed circuit boards. One of them with capacitors C2 '-C5', diodes VD1 ', VD2' and resistor R6 must be installed in close proximity to the antenna socket, and the other - with the rest of the details - must be attached to the side wall of the radio station housing next to the 3Ch transformer. The PA1 microammeter is connected to the device with a two-wire shielded cable, and the shield must be connected to the body of the radio station. For the convenience of connecting the indicator, a socket can be installed on the rear wall of the radio station (there is already a hole for it). A socket from stereo phones will do, it just has one grounded contact and two isolated ones.

In the device, you can use the transistor VT1 of the KP303 series with letter indices G D; diodes VD1' and VD2' - any high-frequency detector or pulse. Trimmer capacitor C4 - types KPK-MP, KT4-25; constants - KM, K10. Resistors R3' and R5' can be SPZ-3, SPZ-19; the rest - MLT. C2-23. Microammeter PA1 must have a total deviation current of 100 ... 200 μA, for example M4247.

Adjustment is carried out in the following sequence. A 51 ohm resistor is connected to the antenna jack of the radio station. In the reception mode, resistor R5' sets the instrument pointer to the zero mark of the scale. Then, a high-frequency signal generator is connected to the antenna socket, tuned to a frequency in the middle of the operating range of the radio station (channels 18-20). Having given a signal with a voltage of 1 or 10 mV from the generator, the microammeter pointer is set to the final division of the scale with resistor R3. Then, using an attenuator, the scale is calibrated in points, decibels or microvolts. If a limit of 1 mV is selected, then the measured voltage range will be 65...70 dB, and if 10 mV - 85...90 dB. In the second case, the scale will be much coarser.

Finally, the transmit power indicator is adjusted. Connect a matched load or a well-tuned antenna to the radio's antenna jack. Capacitor C4 sets the arrow of the device approximately in the middle of the scale. If this does not work, then you will have to pick up a capacitor C3. When going off scale, it is necessary to use a larger capacitor, and with a small deviation, a smaller one or completely remove it.

CHANNEL SWITCH ON HEADSET MICROPHONE

The channel switching buttons of the ALAN-100+ radio station are small in size, and if it is located at a small distance, then it is inconvenient to switch channels. Since the microphone headset is usually located closer to the operator than the radio, the installation of buttons on the headset would improve convenience.

This raises the problem of transmitting switching signals, since there are no free conductors in the connecting cable. You can get out of this situation by using the existing conductors and installing the actuator in the radio station housing.

On fig. 3a shows a diagram of the finalization of the microphone headset. There is a constant voltage on the microphone wire, which comes from a resistive divider located on the main board of the radio station; it is used to power the microphone. By connecting resistors to the microphone, the voltage can be changed within small limits (0,3 ... 0,5 V). The executive device must track these changes and give commands to switch channels.

The scheme of the executive device is shown in fig. 3b. Its main nodes are a DC amplifier on the op-amp DA1 and two transistor optocouplers U1 and U2. The optocoupler transistors are connected in parallel with the radio channel switching buttons.

A constant voltage is supplied to the input of the op-amp through the low-pass filter R1' C1', which suppresses the variable component of the 3H signal. In the initial state, the voltage at the output of the op-amp must be equal to the voltage on the engine of the resistor R4 ', therefore, no current flows through the radiating diodes of the optocouplers. Optocouplers transistors are closed. In this state, the device does not have any effect on the operation of the microphone and buttons, i.e. the radio works in normal mode.

If you press one of the buttons on the PTT, for example SB2, then the DC voltage on the microphone wire will decrease. Op-amp DA1 monitors this change, and the voltage at its output will also decrease. A current will flow through the LED of optocoupler U1, the transistor of this optocoupler will open and bypass the channel switch button "down". The operation algorithm is the same as with the main buttons: a short press switches to one channel, and a long press switches the channels sequentially. Pressing the SB1 button will cause an increase in voltage on the microphone wire. The voltage at the output of the op-amp will increase, current will flow through the LED of the optocoupler U2 and the channel will switch "up".

All parts of the actuator are placed on a small board. Optocouplers U1 and U2 can be of the AOT110, AOT122 series with letter indices A-G; SB1' and SB2 - any small-sized buttons with a self-return, working on the circuit.

Adjustment is carried out in the following sequence. In the receive mode, resistor R2 sets the voltage at the output of the op-amp, equal to the voltage on the microphone wire. Then the same voltage is set on the resistor engine R4. These adjustments are repeated several times until the voltage on the engines of the resistors R1 and R4, as well as at the output of the DA1 op-amp, is equal to the voltage on the microphone wire.

By pressing the buttons SB1 and SB2', make sure that the switching is correct. If during a loud conversation (in receive mode) the actuator will be triggered, it is necessary to select a resistor R3. Its resistance must be reduced by 20 ... 30%.

Author: I. Nechaev, Kursk

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