The 300 hertz bandwidth is measured between the 6 db down points. This is
the normal method of measuring filter bandwidth. It is not unusual to hear
signals down 40 to 60 db from this point. That is why the filter shape
factor is also an important parameter. Filter shape factor is defined as
the bandwidth at 60 db down divided by the 6 db down bandwidth. Really
sharp filters such as the rx340 have shaped factors of 1.2 to 1. I find the
Jupiter 300 hertz filter has a shape factor of about 4 to 1 meaning that the
60 db down width is 1200 hertz.
I also find that if is ok to add a post AF-filter to sharpen the IF filter
if the post filter is not narrower than the IF filter 6 db down bandwidth .
In other words, the AGC pumping problem that we all hate when using a post
AF filter is not a problem if the IF filter is at least as narrow as the
audio filter at the 6 db points.
Carl Moreschi N4PY
Franklinton, NC
----- Original Message -----
From: <jsb@digistar.com>
To: <tentec@contesting.com>
Cc: <ditsnbits@tentec.com>
Sent: Thursday, March 11, 2004 2:04 PM
Subject: Re: [TenTec] tighter filter for Jupiter
> On Wed, 10 Mar 2004, Jason Buchanan wrote:
>
> > Does anyone know if there is a way to get a tighter filter for the
> > Jupiter? I find myself trying to squeeze the bandwidth filter tighter
> > than 300Hz. There are times I wish I had 100Hz! :-)
>
>
> Thanks to all who replied.
>
>
> I would ultimately prefer to see the firmware modified slightly to further
> narrow the bandwidth instead of a post-AF stage filter.
>
> It seems, using MixW to analyze the output viewing the waterfall, that at
> 300Hz the bandwidth is actually closer to 600Hz wide, 300Hz wide either
> side of center frequency. I was hoping the 300Hz filter would be 300Hz
> edge-to-edge, not 300Hz either side of the VFO frequency.
>
>
> thanks,
> Jason N1SU
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