GC_ET_AFX_NeScaf.html
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2018-02-06 11:18:35
2021-01-06 11:55:49
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There are other variations on the use of the family of SCAF chips.
Quoted from "The New England QRP Club" descripton of their NeScaf project:
The integrated circuit at the heart of the NESCaf is made up of two CMOS active filters.
These filters are extremely configurable (low pass, band pass, notch etc).
We have chosen to set up both filters as Butterworth band pass filters and to cascade the filters.
Butterworth filters have the characteristic of constant amplitude in the band pass region,
while the cutoff knee is not be as sharp as if the filter were configured as a Chebychev.
We considered this an acceptable tradeoff,
wanting constant volume out regardless of the bandwidth or center frequency setting of the filter.
There are two on-board trimmer pots. One is used to "calibrate" the center frequency pot.
This allows you to adjust the frequency at which the center detent occurs.
If you are using a rig with a transmit offset and sidetone of say, 700 Hz,
you can use this trimmer to make that the center-detent frequency.
The other on-board trimmer adjusts the audio level into the filters output amp.
Using this pot, you can set the overall gain of the filter.
This can be used to set the filter for unity gain, if desired.
This way, the filter could be switched in and out, and still maintain
a comparable volume level in the headphones.
The NEScaf has no panel mounted volume control of its own.
It is designed so that you use the AF volume or RF gain control on the rig it is being used with.
