EMRFD Message Archive 7224

Message Date From Subject
7224 2012-02-02 19:50:10 Ashhar Farhan Input/Output tuned amplifier
Our contemporary design sense is to use a double tuned or triple tuned
circuits in bandpass filters followed by a broadband amplifier. The
earliest such mention in poplar literature seems to be the CERverters
designed by hayward for demaw's high performance 1.8MHz receiver.
How does one predict the shape of filters cascaded with amplifiers
in-between? Does the shape multiply the bandpass characteristics? Can
one acheive any particular shape (eg Gaussian) by controlling the
'active' coupling between the stages? My sense is that the presence of
a unidirectional element between the resonators will result in simple
multiplication of the filter's shape by a factor of two (in dbs). Is
this correct?
- Farhan

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7226 2012-02-03 10:06:09 Alex P Re: Input/Output tuned amplifier
From memory, Terman addresses your question to some degree in I believe his first issue circa about 1938 (?). As I recall, putting cascade amps with tuned interstage tanks will increase Q, and bandpass gain quite substantially. He also addresses more than just double tuned tanks and interstage coupling. I don't recall if he had more sophisticated than first order design equations but it's a good first start to review. I would model the circuit up in SPICE as a first approximation. Regarding unidirectionality, practically speaking, there will generally always be some degree of signal reflecti