In a message dated 2/2/2003 12:11:26 PM Central Standard Time, n1eu@yahoo.com
writes:
> With respect to the Omni VI+, AB9M mentioned "TenTec
> for that reason provides narrow roofing filters in the
> first IF. With the 500 Hz or more likely the 250 Hz
> filters selected"
>
> I don't think it's quite right to call these cascaded
> 9Mhz 1st i.f. filters "roofing filters"
>
> There's actually a wide (15khz?) "roofing filter"
> before the 2.4khz 9Mhz filter. A few folks have
> experimented (but nothing conclusive ever published)
> with replacing that wide roofing filter with a
> narrower filter to improve close-in dynamic range
> performance.
>
You are correct, its not quite right to call them roofing filters, but the
resulting bandwidth selectivity allows the desired in band (250 Hz or 500 Hz
wide) signal to pass though an amplification stage and mixing function
without the 9 MHz amplifier -- mixer (which feeds the 6 MHz PBT) being driven
into a nonlinear condition from pileup 2A-B or A+B-C S9+20 signals that are
passed by the traditional 15 kHz filter.
I apologize for not being technically correct or articulate in my
description. Not having a BSEE or PHD is somewhat of a liability in technical
writing.
Gary Huber - AB9M@aol.com
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