Common Base Transformer Feedback Norton Amplifiers

For about a year I have been experimenting with extremely high intercept amplifiers using 2N5109 bipolar junction transistors (BJTs). These kinds of amplifiers, known as common base transformer feedback (CBTF) amplifiers, and also known as common base noiseless feedback amplifiers, if properly designed and used, offer MW DXers (and SW DXers, though their needs are not as extreme as MW DXers) amplifiers with extremely low levels of 2nd and 3rd order intermodulation distortion (IMD2 and IMD3), which, in turn, offer much higher levels of strong signal handling performance than have been available previously. CBTF amps can provide greatly improved performance for balanced two foot air core loop amps, for low-gain tuned preselector amps, for broadband phasing system amps, and for other similar applications where extremely high 2nd and 3rd order input intercepts (IIP2 and IIP3) are needed. Appropriately configured, a single BJT CBTF amp can have IIP3 greater than +35 dBm throughout the MW band and IIP2 greater than +46 dBm throughout the MW band. With a pair of BJT CBTF amps configured push-pull, IIP2 greater than +95 dBm can be achieved throughout the MW band. The purpose of this note is to summarize my experiences with CBTF amps using 2N5109's, and to provide enough information for other DXers to construct and use these kinds of amplifiers.