Encyclopedia of radio electronics and electrical engineering / Civil radio communications
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Sooner or later, the owners of YOSANs, ALANs, and other foreign-made radio stations have problems with a microphone headset. The radio station "hangs" when switching from reception to transmission, the channel switching buttons are junk, the microphone "crunches", etc. But since a new branded headset, most likely, will not even be offered, and repairing the old one will cost a pretty penny at best , then it remains to do it yourself.
On fig. 1 shows a diagram of the microphone headset of the YOSAN-2204 radio station (pin numbering - according to the microphone connector). Note that in the manufacture of the PTT there is no need to strictly follow the ratings indicated here. Moreover, those of them are marked with an asterisk, which, most likely, will even have to be changed. This applies primarily to the capacitor C1. To improve speech intelligibility, a capacitor C1 with a capacity of 1000 ... 2000 pF is often installed. The voltage across the electret microphone depends on the resistance of the resistor R1. If a different microphone is used, this voltage may need to be changed.
Switch "reception-transmission" SB1 - PKn61 without fixation. SB2 and SB3 - buttons for switching the working channel "up" and "down" - work on a circuit and have a pusher 10 mm long. Electret microphone BM1 - type CZN-15E (from a "Chinese" handset). All resistors - MLT-0,125. Capacitors C1 and C3 - KM-6, C2 - K50-40.
All elements of the microphone headset are installed on a printed circuit board (Fig. 2), made of double-sided foil fiberglass 1,5 mm thick. The foil under the parts is used only as a common wire. In places where the conductors are passed, samples are made in it - circles with a diameter of 1,5 ... 2 mm (not shown in Fig. 2). Foil connections are shown as black squares, and "ground" jumper wire positions are shown as black squares with a light dot in the center.
The mounted board is installed on the front panel of the tangent - a plate with dimensions of 37x73 mm, made of high-impact polystyrene 2 mm thick. Polystyrene racks 2,1 ... 9,5 mm high with metal inserts pressed into them with a thread for the M10 screw are glued to the plate in the appropriate places (see the position on the board of holes with a diameter of 2 mm). The glue is made from the same polystyrene, dissolving small pieces of it in solvent 647. This high-strength connection with almost invisible seams allows you to assemble a well-looking PTT body.
At the free end of the panel (it is 11 mm longer than the board), in one way or another, a five-core shielded cord 1 ... 1,5 m long is fixed. shielded wire of a suitable diameter, and then all this is dragged into a PVC tube. In the front panel, the tangents make holes for the free passage of the pushers of the SB2 and SB3 buttons and a hole in front of the microphone with a diameter of 3 ... 4 mm.
The case-cover of the tangent in the form of an open box is glued from the same high-impact polystyrene 2 mm thick. According to its inner contour, a groove is selected into which the front panel will be inserted. In places where the SB1 switch button and the cord are skipped, appropriate cutouts are made in the case. All elements of the PTT (body-cover and front panel with the board) are fastened together with an M2 screw with a countersunk head (an M2 threaded hole in the board is for it). Dimensions of the tangent - 76x40x17 mm.
Any electret microphone with a sufficiently high sensitivity is suitable for the YOSAN-2204 radio station. But not every microphone satisfies this requirement, of the domestic ones, perhaps, only "Pine". This limitation can be easily removed if the electret microphone signal is pre-amplified.
On fig. 3 shows a diagram of a microphone headset for the YOSAN-2204 radio station with a built-in amplifier. The DA1 chip is a micropower operational amplifier, which is powered by the radio supply voltage. Its gain is determined by the feedback elements: resistors R5-R7, capacitors C4 and C5. Resistor R9 sets the desired output level.
The tuning resistor R9 is used of the SP3-38b type, the remaining elements are the same as in the previous design. The printed circuit board of the PTT is shown in fig. 4.
To control the output signal level control, a hole with a diameter of 3 ... 3,5 mm is made in the front panel of the PTT.
Author: Yu.Vinogradov, Moscow
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