In article , starman wrote:
Mark Zenier wrote:

Somebody posted the schematic here in the newsgroup a few months back.
Interestingly simple set. It's got a tuned dual FET cascode RF amplifier.
So a preselector or pre-amp won't benefit it too much.

Why do you think the first RF circuit in the DX-160 precludes using a
passive preselector?

Because there are two tuned circuits, each using a segment of the
main capacitor gang, (the input transformer, and the output of the
amplifier). Both are feeding the gates of FET amplifiers, so are (or
have the possiblity of being) high impedance and therefore high Q.

The fact that there's an "antenna trim" control, (which really usually
compensates for mistracking of the two tuned circuits) indicates that
they're pretty sharp, at least for an LC tuned circuit. Likewise, the
bandspread capacitor is two sections, one in parallel with the main
oscillator tuning, the other in parallel with the RF amp output tuning
cap. So the Q must make the bandwidth narrower than the 1/2 MHz or so
that, (as I remember), the bandspread covers.

Mark Zenier Washington State resident