Howard wrote:

On Tue, 21 Sep 2004 09:22:41 GMT, John Steffes
wrote:

Howard,

The preselectors we have dealt with have been , in general, active. They
have used positive feedback to increase the "Q" of the resonant tank
circuit providing greater selectivity. It is reasonable to accomplish
this using no positive feedback (bandpass design) as you suggested.

John


John,
Thanks for the reply, nice to know I wasn't off-base in my thinking.

Howard

A shortwave preselector can be either active or passive. The former
usually has an amplification stage followed by an impedance matching
output circuit in addition to the tuned circuit(s). The passive type has
only the tuned circuits. Some preselectors can be both active or passive
if the amp' circuit can be turned off (lowered to unity gain) or
completely bypassed. The main advantage of any preselector is it's
bandpass filtering (tuned circuit) which provides a means of removing
signals outside the frequency range (band) that the user wants to hear.
This is particularly useful for receivers (usually portables) that don't
have a good antenna input circuit to accomplish this filtering process
internally.


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