[TenTec] Roof filters

[Carl Moreschi]

The algorithm for centering the DSP filter is a little different.

If X is the spot tone frequency and BW if the filter width, then
if BW/2 < X then the filter center is X
if BW/2 > X then the filter center is BW/2

So in your example, the 1800 DSP filter would center at 900 even though your
sidetone was 400.  This is what removes the signal below zero.  The 1800
roofing filter always centers at your sidetone.  So the DSP filter is
removing the audio below 0, and the roofing filter is cutting the upper edge
at 1350 as you said.

Carl Moreschi N4PY
121 Little Bell Drive
Bell Mountain
Hays, NC 28635
----- Original Message ----- 
From: "Bill Tippett" <btippett at alum.mit.edu>
To: <tentec at contesting.com>
Sent: Wednesday, March 15, 2006 9:45 AM
Subject: [TenTec] Roof filters


> I wrote:
>   > TT 1800  - 1400 Hz (in CW mode only, 1900 in SSB)
>
> YT1NT replied:
>   >Roofing filter has one BW in CW, another in SSB?
>
>          I finally figured out what is going on.
> Orion always automatically centers the passband
> of the roofing filter selected and also automatically
> truncates any response below 0 Hz.  If you have Spot
> Pitch set to X, the upper edge of the 1800 Hz filter
> (which is actually ~1900 Hz BW) will be at X + (1900/2).
> For example, if I am listening with Spot Pitch = 400,
> the upper edge is 400 + 950 = 1350 Hz.  The lower edge
> is still 0 Hz, making it appear that the filter only
> has 1350 Hz BW.  In fact it is actually 1900 Hz but
> the LF response is truncated below 0 Hz.
>
>          At any rate this makes the 1800 Hz filter
> a very nice filter to use for rapid scanning in CW such
> as when doing S&P in contests.
>
>                                  73,  Bill  W4ZV
>
>
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