Marcelo,
The FT-1000 is a quadruple conversion receiver.
The Second and Third I-F sections have crystal or mechanical filters to
shape the waveform of "business" going through these amplifiers.
The fact that owners of these radios can chose what filters go where
makes them unique.
(Not the owners, the radios.)
When you select a Filter button, the radio diverts the receive
information along a pathway that goes through a certain filter POSITION
in the second and third I-F amplifiers.
You could very well choose to put narrow filters in the wide SSB
position, or vice-versa. However, the preponderance of operators choose
to put specific-width filters in certain of these positions that com up
matching the button suggestions on the front panel, meaning wide is wide
and narrow, narrow.
If you look at the INRAD.COM catalogue you will see various filters
available in their FT-1000 department.
Some operators want razor-tight slots for CW work and go all the way to
125 Hertz devices, while other ops like the hifi-SSB world and choose
filters that allow broadcast width signals with gentle slopes.
All-in-all, the second and third I-F filters act together, and pushing
the filter buttons, routes signals through various parts of the radio
that allow you to tailor your listening experience quite widely.
Hal Mandel
W4HBM
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