Encyclopedia of radio electronics and electrical engineering / Civil radio communications
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Controlling a car HF, VHF or CB radio station in stationary conditions can be made more convenient if you equip it with a stationary headset. In the described version, the desktop microphone is designed to work with the YOSAN-2204 CB radio station, but with minor modifications it can be used with other KB, VHF and CB radio stations.
Operating a car radio used as a stationary radio can be much more convenient if you use a desktop microphone with a key or control button.
On fig. Figure 1 shows a schematic diagram of such a device for the YOSAN-2204 radio station. It consists of an amplifier for a dynamic microphone and a remote control for the transmit-receive switch.
The amplifier is based on DA1 - a low-noise operational amplifier K1407UD2. Its gain is determined by the ratio of the resistance of resistors R4/R6 and, with the values indicated in the diagram, is equal to 20. If necessary, it can be increased by 5-10 times if a resistor R4 of higher resistance is used.
The low-frequency limit of the amplifier's passband (FH) depends on the parameters of the R6C4 circuit, and the high-frequency (FB) limit depends on R8C6.
The “Receive-transmit” switch is relay K1, which is controlled remotely by a desktop key (button) SB1 or a foot pedal SB2. The contacts of this relay and the SB3 and SB4 buttons (channel switching) are included in the same way as in the YOSAN radio station.
The elements of the device are mounted on a printed circuit board made of double-sided foil fiberglass (Fig. 2).
The foil under the parts is used only as a common wire. Connections to it "grounded" terminals of capacitors, resistors, etc. are shown in black squares. Before installing the DA1 chip, its pin 4 is bent to the side. Squares with a light dot in the center show jumpers connecting individual fragments of printed wiring to a common wire. In places where the conductors pass through this foil, protective circles with a diameter of 2 ... 2,5 mm should be etched (not shown in Fig. 2). Oxide capacitors are installed over holes with a diameter of 3,5 mm, and their leads are bent and soldered to the pads.
All fixed resistors are MLT-0,125, trimmer R9 is SPZ-386. Capacitors C1 and C2 - any oxide of suitable sizes, C3, C4, C6 and C7 - KM-6 or K10-176, C5 - KM-5 with multidirectional leads or similar (the capacitor is installed on top of the microcircuit). Relay K1 - RES47 for operating voltage 12 V with any passport. The VM1 dynamic microphone can be almost anything.
The mounted printed circuit board is secured with three M2 screws in a plastic housing box (Fig. 3). The pushers of the SB3 and SB4 buttons must be long enough to extend through the front panel of the housing. Experience has shown that a headset assembled in this way does not require any additional shielding.
The cable connecting the device to the radio station can be very short - 0,3...0,5 m. It is not difficult to make it yourself. Five soft conductors in fluoroplastic insulation are inserted into the shielding braid and the whole thing is pulled into a polyvinyl chloride tube with a diameter of 5...6 mm. The length of the cables to the SB1 and SB2 buttons (two conductors in a thin PVC tube) is practically unlimited.
The most expensive part of the headset (not counting the microphone) will be its only proprietary part - a connector for connecting to a radio station.
The designs of SB 1 and SB2 - desktop button and foot pedal - can be very different. As the contact pair itself, it is recommended to use a button in which the closure occurs with a click, for example, PKN-150-1.
Setting up the device is easy. You just need to install resistor R9 in a position that will correspond to the best modulation of the signal - not too small or, conversely, excessive with distortion and “overshoot” of the signal into adjacent channels. This is done based on feedback from correspondents. If in this case the R9 slider is in the extreme position, then by selecting the resistor R4, the gain of the operational amplifier is increased or decreased so that the desired gain corresponds to the position of the R9 slider that is more convenient for precise adjustment.
Author: Yu.Vinogradov, Moscow
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