On Aug 25, 2009, at 10:59 PM, Jeff Blaine AC0C wrote:
> A common data point seems to be the Inrad/Elecraft K3 filter @ 250
> hz. Looking at the top of that filter, it is about -3db down at 240
> hz and -6db at about 370. Guys seem to have no negative comments
> about that filter.
The skirts of the stock K3 filters are not especially tight. But they
don't need to be. They are basically roofing filters to keep the A/D
converter of the "real" software (DSP) filters from clipping. Steep
skirts are much easier, and more accurately, obtained by using DSP
math than by using a limited number of poles from a crystal filter.
Jim K9YC has a nice write-up on filters, with curves for the FT-1000MP
(stock and Inrad, and how filters can be cascaded in the MP) and K3.
See here
http://audiosystemsgroup.com/FilterTestNotes.pdf
I'd stocked my FT-1000MP with some Inrad filters from the days when I
was still depending on narrow I.F. filters. (The Inrads are "tighter"
than the equivalently spec'ed Yaesu filters.) As a consequence, I
still have the following compliment for my MP, though I seldom need
the narrow filters anymore. With RTTY, I'd used the 500 Hz (Yaesu)
at the 8215 kHz I.F., cascaded with the 400 Hz (Inrad) at the 455 kHz
I.F..
> 455 kHz IF
> YF110CN 250 Hz CW 250
> IRC 703C 400 Hz CW 500
> Empty - 2.0
> XF115S Stock 2.4
>
> 8215 kHz IF
> IRC 708B 250 Hz CW 250
> XF501 Stock 500
> (soldered)
> IRC 709B 2100 Hz SSB 2.0
> XF262 Stock 2.4
> (soldered)
>
> 2nd Rx
> YF115C 500 Hz CW
For my K3, I have the 400 Hz, 2.8 kHz and 6 kHz roofing filters.
73
Chen, W7AY
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