[Elecraft] APF vs 10 Hz DSP, why they don't sound the same

[Frank Ross W4NHJ]

If you have an SDR type  panadaptor using the IF out signal, you can try a 
peaking filter by downloading and running WinRad software.  WinRad has a 
peaking filter that works great.

Frank - W4NHJ

----- Original Message ----- 
From: "Bill Tippett" <btippett at alum.mit.edu>
To: <elecraft at mailman.qth.net>
Sent: Sunday, August 16, 2009 7:38 AM
Subject: Re: [Elecraft] APF vs 10 Hz DSP, why they don't sound the same


> > More generally, the APF proponents seem to have the problem that they
> treat it almost as magic.  If they could characterise what it does in
> terms of filtering, AF gain adjustment, distortion etc. it should be
> possible to simulate it in DSP, subject only to having enough processing
> power.  In particular, peaking just seems to me to mean turning up the
> AF gain in parallel with reducing the bandwidth. If that is all that it
> is doing, and if the K3 has soft AF gain controls, a plugin box could
> issue both commands in parallel.
>
>         The circuit in question is on page 54 of the FT1000 schematic 
> below:
>
> <http://www.radioamateur.eu/schemi/FT1000_user.pdf>http://www.radioamateur.eu/schemi/FT1000_user.pdf
>
> The APF is around Q3016-2 (including Rs 3062, 3065, 3067 per the
> "un-modification" sheet on N1EU's website below).  The circuit
> schematic above has *not* been modified to the (incorrect) values
> shown in the Yaesu service bulletin.
>
> http://n1eu.com/Mods/apf.pdf
>
> The FT-1000's APF is generally regarded by many as the best APF ever
> done.  It should be possible to plug this into a circuit simulator
> and generate a frequency response plot that Lyle can emulate in the
> DSP.  I have a feeling that this is a very narrow and high-Q response
> that is on the verge of ringing, but it should be possible to
> duplicate the circuit in the DSP.
>
>                                         73,  Bill  W4ZV
>
>
>
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