tr switch

The project I present here is my attempt at a universal QRP T/R switch. The idea is to take care of the essentials, so that any QRP (i. e. , less than 10W) receiver *AND* CW transmitter can be connected, and work seamlessly. These are what I considered the `essentials` to be: The operational scenario would be as follows, and could easily be applied to any QRP
tr switch - schematic

transmitter (or transceiver used as a transmitter) and any receiver (or transceiver used as a receiver). But the device is especially designed to accommodate a simple transmitter and receiver, each having few embellishments, and requiring none. Operationally, here`s how a typical case would work: When Steve Weber, KD1JV, used three 2N7000 power MosFETs in the final of his AT Sprint transceiver, and managed to produce 6 watts with same (4W at 20 Meters), it really opened my eyes to these little devices. I had always thought of these as audio or power-control devices, but now I began to think in a different direction. One thing that immediately occured to me is that these devices might be configured in such a manner as to provide an "on/off" switch to RF energy between the transmit line and the receiver`s antenna input. They could additionally provide protection to the receiver, by shunting any unwanted energy that might make it as far as the receiver`s antenna input. This led to some experimenting in SPICE, and eventually to the following essential T/R switch circuit: Let`s review the schematic. The transmit signal is tapped at the transmitter output - the transmitter remains connected to the antenna at all times - and arrives at the left "TX-ANT" port. Q1 serves to connect the receiver antenna port (right, "TO RX") to the antenna (during receive), or isolate it (during transmit). Because Q1 does not completely isolate the...

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