Transceiver Circuits

RS-232 Laser Transciever circuit

Laser based projects used to be expensive, until the development of solid state lasers. This project is designed for the entry level laser experimenter. The circuit allows any two computers with serial (RS-232) communication capability to communicate over 200 meters using a laser beam. A low cost transmitter only circuit is also presented here for use in one way communication and other laser based projects. If you are like me and always wanted to buy a laser pointer to play with, but could never find practical uses for one, here are a couple of circuits to convince you to finally make that purchase. Before we begin, however, it is necessary to give a word of warning: Never look directly into the laser beam as eye damage may occur. ..

75 meters Band SSB transceiver

In general, the transceiver switches the 4-element 1500 ohm xtal BPF ends between the inputs and outputs of the two SA602s to reverse the signal flow for R/T operation. Since no IF amplifier is used in the design, 20 dB of additional receiver gain is produced by the 2N2222 receiver RF amplifier, while automatic gain control (AGC) is produced by the peak DC swing of the LM386 output passed through a rectifier and filtered by a capacitor and fed to the gate of a BS170 enhancement mode FET acting as a variable resistor across the input of the LM386...

30m Band CW-Transceiver

This simple QRP transceiver for the 30 m band did not result from a detailed requirement profile. I simply had some NE592 broadband amplifiers in my junk box, waiting for an application. After performing some tests, that application was quickly found: The amps should become part of a superhet transceiver. There is need for amplification in several places in such a rig, starting from the IF, over to the AF, and up to the RF for driving a push-pull final. The high crystal frequency of 14318 kHz allows a pulling range of 20 kHz without special tricks. You can tune the reception range from 10100 kHz to 10120 kHz using the coil L2. Some tests with the number of turns of the coil are recommended here, such tests are commonplace when setting up a VXO...

Remote tuning transmitter

This project consists of a wide range receiver and one transmitter. Together they will form a unit which will help you tuning your homebrewed transmitter. The most difficult part of homebrewing is the tuning part of the transmitters. How should I design and tune the output filter of my transmitters? Well, you can use a 50 ohm dummy load and tune the transmitter for best performance. When you connect your antenna, which probably won't have 50 ohm resistive load and you will lose lot of power. Okay, you have 100W so what! You will still be able to transmit to your neighbour 1km away. 88-150MHz Receiver, 125MHz transmitter. Both the receiver and the transmitter frequency is set by a frequency PLL synthesizer. This will give very good stability and easy tuning. In this case I use a UMA1015 synthesizer. This synthesizer do have two separate PLL units. ..

Transceiver for 20 m band

The transceiver is composed by three single sided printed boards 100x70 mm, theese may be stacked so as to reduce the overall size of the metal cabinet. I suggest to employ small size components (1/4 W resistors, 2,5 mm capacitors, ) wich should fit better on the PCB boards. On the front panel you may place the tuning pot with its reductor gear, the gain and volume controls, the Key and earphone jacks. The power and antenna connectors may be housed on the back panel. The basic version makes use of a Colpitts fet oscillator and a buffer (2N2222) driving the RX and TX circuits...

40 meters CW Transceiver

This project describes a little QRP transceiver full legal power” (5 W at 12 V) for the 40 meters band. The RIG may be built in a gradual manner, in fact it is divided in two main modules, or you may also complete only the RX module. The RX section is designed so as to allow receiving both SSB and CW signals on the whole 7 MHz band. The tuning may be done using only an HF receiver, but if you have at your disposal a frequency meter and a signal generator, you could do a better job. If you are interested in further informations, or to get the PCB masters, please contact me at my E-mail box...

HF phone rig for 20-40 meter band

A simple project, within most of homebrewers capabilities. Very simple tuning, a single stage to align, besides VFO frequency adjusting. Easy to find, cheap components. Reduced dimensions and low power requirement, a totally portable rig. It's worth while to spend some words about the DSB modulation. It's simply a type of amplitude modulation (AM). It is common knowledge that an AM signal is composed by a carrier and two sidebands, wich take the whole information. The figure below represents an AM signal at 14.000 KHz, modulated with a 5 KHz bandwide BF signal...

Transciever Relay Sequencer

When the sequencer is not activated (The radio is receiving) K1 is in its N\C position, suppling DC voltage to L1 forward biasing D6, D7 and then flowing through R13 and R14 (As shown in blue arrows). C3 and C4 are used to block the DC. Once D6, D7 are conducting the RF signal is able to pass from the RX IF port to the radio input / output port (As shown in red). When the sequencer is activated (The radio is transmitting) K1 is in its N/O position suppling DC voltage to L2 forward biasing D14, D15 and then flowing through R29 and R30. Once D14, D15 are conducting the RF signal is able to pass from the radio output port to the TX IF port (As shown in green)...

The circuit is an VXO with buffered output. It operates on 20-meter amateur radio band with the output voltage about 0.2 Vp-p. The crystal frequency is pulled by tuning the variable capacitor CV1 about 36Khz with only one crystal (Y1), and 250Khz by using two crystals Y1 and Y2. The first configuration stability is much better than using two crystals. However, if you need more frequency variation, use two crystals and you have to pay the cost by getting less stability. ..

The PMR VHF transceiver Motorola Radius M110 (in further text referred as M110) was manufactured by Motorola GmbH therefore being an European radio. Since many professional radio service users has replaced this transceiver with newer gear, a considerable number of M110 has appeared on HAM flea markets. M110 is a simple yet fine transceiver with pretty good receiving performance and it would be a waste to throw it away or to use it just as a source of electronic components instead of giving it a new life in the HAM shack...

This set of two circuits from the basis for a very simple light wave transmitter. A LASER beam is modulated and then aimed at a receiver that demodulates the signal and then presents the information (voice, data, etc..). The whole thing is very easy to build and requires no specialized parts execpt for the LASER itself...

The circuit can be culled from the MCP2120 developer`s kit user`s guide. It is on page 51 of document DS51246A. If you don`t want to use an integrated transceiver, there is a circuit for you to build your own with a seperate ir led and detector. Make sure you realize that irda leds are at a specified wavelength and need a very quick switching time (i.e. ir leds for remote controls are not suitable)...

The RS485 interface standard is designed to handle a 7V to 12V input signal range; however, in practical systems, ground potentials vary widely from node to node, often exceeding the specified range. This can result in an interruption of communications, high current flow through ground loops or worse, destruction of a transceiver. Guarding against large ground-to-ground differentials calls for an isolated interface. A new surface mount device, the LTC®1535 isolated RS485 transceiver, provides a one-chip solution for breaking ground loops and achieving a wide input range...

Pressing the pushbutton of the transmitter, a sound and/or light alert is activated in the receiver. The system uses no wiring or radio frequencies: the transmitted signal is conveyed into the mains supply line. It can be used at home, in any room from attic to cellar, simply plugging transmitter and receiver in the wall mains sockets. Transmission range can be very good, provided both units are connected to the mains supply within the control of the same light-meter...

The LTC®1387 is a single 5V supply, single-port, logic-configurable RS232 or RS485 transceiver. The LTC1387 features Linear Technologys usual high data rates (120kBd for RS232 and 5MBd for RS485), a loopback mode for self test, a micropower shutdown mode and ±7kV ESD protection at the driver output and receiver inputs. This part is targeted at handheld computers, point-of-sale terminals and applications that require a minimum pin count and software-controlled multiprotocol operation...