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MagicBox T/R Switching System

This system is the result of some brainstorming with Terry Fletcher, WA0ITP and Joe Porter, W0MQY at the Dayton Hamvention in 2009. We were talking about kits that might be suitable as revenue generators to fund the Ozarkcon activities in 2010 and beyond. The "MagicBox" project is the result. It is an all solid state, Transmit/Receive switching system that allows one to connect single band CW transmitters and receivers together to turn the pair into a transceiving station, "like magic". The system can be used on any band from 160 through 10 meters and up to 10-watts of RF. It can handle both solid state and cathode keyed, tube transmitters. It supports full QSK CW up to about 50 WPM. And, a non-QSK mode is also provided, for those who don't like QSK CW.

MB Front View
There are five pieces of functionality within the system. First, is a keying circuit to turn on the transmitter. Second, is a PIN diode switch used to connect the transmitter to the antenna so that it can transmit and also to isolate the output impedance of the transmitter from loading the receiver. Third, is a four element, series-shunt switch that disconnects the receiver from the antenna and shorts the receiver input to ground while the transmitter is transmitting. Forth, is another series-shunt switch (three elements) used to disconnect the receive audio from the speaker (headphones) during transmit. Fifth, is a sine wave audio oscillator and series switch that supplies side tone audio to the speaker (headphones) during transmit so that transmit keying can be monitored. All of the control timing for the system is supplied from an AVR ATtiny2313 microprocessor.

This MagicBox T/R System can be ordered from the 4 State QRP Group here!!
MB Rear View



160 through 10 meter operation
5.3" X 4.0 " PCB, fits TenTec TP-41 case
Approximately 120 parts
Beginning builder skills level project
Construction time approximately 8 hours

Power Supply   10-15 volts dc; 120 milliamps

RF Section

Receive Mode
Antenna to Receiver Input Loss: Less than 2 dB, 1.8 - 28 MHz
Transmitter to Receiver Input Isolation: Greater than 25 dB, 1.8 - 28 MHz

Transmit Mode
Transmitter Output to Antenna Loss: Less than 0.25 dB, 1.8 - 28 MHz
Antenna to Receiver Input Isolation: Greater than 90 dB, 1.8 - 10 MHz
Greater than 85 dB, 14 MHz
Greater than 80 dB, 28 MHz

Audio Section (32 Ohm source and load)

Receive Mode
Receiver Audio Loss: Less than 2 dB

Transmit Mode
Receiver Audio Isolation: Greater than 200 dB


QSK Mode   Up to 50 WPM

Non-QSK Mode   1 second receiver delay

Transmitter Types   Solid state or cathode keyed tube

Schematic Diagrams
MB Schematic Page 1
MB Schematic Page 2

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