MagicBox

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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.
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!!

Specifications General System 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 Keying QSK Mode Up to 50 WPM Non-QSK Mode 1 second receiver delay Transmitter Types Solid state or cathode keyed tube
Schematic Diagrams




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