Back in 2009 Wes Hayward and Bob Kopski designed a termination insensitive amplifier block for use in BITX-like transceivers. Farhan urged me to use it. The advantage of this design is that the input impedance stays at 50 ohms no matter what you hang off the other end. That's very helpful, especially when you start trying to get specific impedances at the ends of crystal filters. I'm planning on using this circuit in my next BITX. This morning I was playing around with it in LTSPICE. The "mirror" feature in that program is quite helpful when you are working on circuits like this!
Here is the article by Wes and Bob that describes this great circuit:
http://w7zoi.net/bidirectional_matched_amplifier.pdf
Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20
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