To connect CB radio to the telephone line used telephone interfaces. With a simple version of such a device introduces the proposed article. It should be borne in mind that non-certified devices to connect to the telephone network of General use is impossible. The interface can only be used on departmental and PBX.
The need for the development of the telephone interface has arisen in the absence of a simple and cheap device for connecting the radio range of 27 MHz to the telephone line. The device, manufactured by foreign firms, for example, type SC-900 LMR-2, road. However, they provide a link subscriber's ID with the subscriber telephone network in automatic mode. A similar structure of the Russian production cheaper, but their quality leaves much to be desired. In addition, in conditions of strong interference operation of any interface is only possible in manual mode, i.e. the Manager dials the number and connects the station with the telephone line. In this regard, and an interface was developed operating in manual mode. The interface is made in three versions, connected to the stations of different types, showing the reliability and high quality of communication. Interface design was technologically advanced, easy to repeat and uncritically to the types of parts used. Extensive customization options allow you to connect the interface to virtually any radio station with minimal changes. With careful tuning is provided by the communication quality is not worse than the types of interfaces SC-900 LMR-2.
The interface is connected to the radio via the microphone Jack without changes in the design of the station itself. It provides two-way simplex communication station with subscriber urban or long-distance telephone network, and the connection Manager with the subscriber's ID. All standard functions of the radio are fully preserved. Dialing produces Manager with the individual telephone (if the interface is designed as a separate structure) or directly from your phone-interface (if the interface is built into the phone).
Diagram of the device shown in the figure. Below are transcripts of some of the signs of the contacts of the connector, which is connected to the microphone of the radio station:
- PTT (TX) - switch on the transmission. When applying a low level on this pin, the radio goes into transmit mode. - SKP (RX) - switches to the reception. When applying a low level on this pin there is a transition station in the receive mode. As a rule, through it is shorted to ground circuit built into the radio heads, and, consequently, this contact is present, the voltage of low frequency.
- MIC - contact microphone. Typically used electret microphone, so on this pin may be a constant voltage.
GND - standard notation common wire of the radio station.
- 13.8 V - power radio station.
The heart of this device detector signals A1 and A2. The detector A1 receives a signal from the radio station, and A2 with a phone line. The circuitry of these blocks are similar, they differ only by the fact that A2 has an additional signal amplifier transistor VT3.
Consider the work of one of the blocks, for example A2. The signal passes through capacitor C6 to the transistor VT3, amplifies them and goes to the doubler rectifier voltage (VD4, VD5). A composite transistor VT4VT5 is opened and relay K2, which produces the necessary switching. Parallel relay included CBE-todiode HL3, serving as the indicator relay.
The switch SA1 is used to select the operation mode. In the depressed position mode "Interface", and pressed the radio and the phone perform its basic functions.
If a signal from the line, the relay K2. It is their contacts K2.1 disconnects from the radio station A1 (to prevent false positives K1), contacts K2.2 closes the PTT output to a common wire that switches the radio in the transmit mode, and the contacts of K2.3 connect the microphone input of the radio station to divider transformer T1 (i.e. to the telephone line). Contacts K2.4 disconnect A1 from the power source and provide charging of the capacitor C2 to better relay K1.
If a signal from the radio station (use the SPK output, which has a low frequency voltage), relay K1, it is their contact To 1.1 connects the output SPK to the transformer T1, and the signal from the radio goes to the telephone line. The Contacts K1.2 is disconnected from the line block A2 to prevent false triggering of relay K2.
The interface may be formed as separate structures or integrated into your telephone with push-button and automatic dialer.
The first option is to embed the interface in your phone dialer. Contacts SA1.7 when operating in mode interface connect the phone through the resistor R12 is necessary to reduce the shunting effect of the talking part of your phone to use interface and the ability to listen to the Manager talks through the interface. Contacts SA1.8 turn off the microphone of the handset, which increases the stability of the interface. In this embodiment (shown in the diagram) it is not possible to dial a number in the "Interface".
The second option is the embedding of the interface in the phone with a rotary dialer. In this case, you can dial the number in the "Interface". To implement such an option should the findings shown in the diagram "To a telephone, connected to a communication node of the phone, and conclusions "To the telephone line to the phone dialer after. To line the device is connected as usual.
The third option is the connection interface is made as a separate consoles. The first variant is characterized in that the contacts SA1.8 is not activated, the microphone is not disabled, so it is possible the emergence of self-excitation.
Transistors VT1-VT5 can be any of the series KT315, CT, KT3102. Relay K1 - RES-22, passport RF, K2-RES-9, passport RS. The switch SA1 - P2K or any eight changeover contacts.
The transformer T1 is any compact transition transformer from a transistor radio. The primary winding should be with less resistance, and the secondary - large. The resistance of the primary winding is in the range of tens of ohms, and the secondary - hundred ohms. It is possible to use a transformer of 1:1, but in any case, the resistance of the primary winding should not be less than 50 Ohms.
Properly mounted, the device begins to work immediately and does not require any adjustment, but due to differences in radio stations, it may be required.
There are five points in which you need to break the chain to ensure normal operation. These points are marked on the diagram A - D. the Circuit at point b will have to be broken in case of excitation of VLF radio stations in the "Interface". At point G to break the circuit in case of the emergence of self-excitation in the transmission mode (for example, YOSAN-2204 or another station with a condenser microphone). With fuzzy actuation of the relay K1 is necessary to break the chain at point D. If the electret microphone is not and is not required to file a diet, you need to break the chain at point B.
Resistor R6 are selected on the optimal level of the signal in the microphone input of the radio station within 1.5... 10 kOhm depending on the type of radio station. The resistance of the resistor R6 should not be less than 1.5 ohms to avoid failure of the circuits of the radio station.
The selection of timing capacitors C2 and C8 in the range from 2 to 20 µf is necessary to achieve reliable operation of relay, as well as to find the optimal time of its release. It is desirable to apply capacitors foreign production, as Russian do not provide the required stability of capacitance.
A variable resistor R7 sets the threshold signal from the telephone line. Makes sense to bring this resistor on the front panel, as the level of the signal from the PBX can be changed and therefore the need to adjust the threshold of the relay K2.
If the connector on the radio station output power (at 13.8 V), to file back this voltage (connector type MegaJet-2701) or connect the interface to the separate power supply wires.
It happens that the interface does not work correctly when connected to the contact SPK. Then, instead of SPK output is connected directly to the embedded dynamic head of the radio station. For this we need to break the chain at point a and connect the dynamic head-to-point connection of the contacts K1.1 and K2.1. In this case, break the chain and at the point B. you May need to pick up a transformer T1, if not enough signal level to phone line.
Connecting the interface to the radio and PTT button to the interface must be performed five core shielded cable. In the case of unshielded cable, you may need to disable the microphone circuit from PTT button (due to crosstalk) in receive mode. For this you can use a separate small relays with voltage of 12 V (RES-15, etc.) by connecting the winding to the power supply pin and to the PTT contact, naturally, after the switch SA1.1.
Author: S. Lushnikov, Blagoveshchensk, Amur region; Publication: N. Bolshakov, rf.atnn.ru