Re: external DSP audio filters (was Re: [RTTY] AA5AUContestNotes for CQWW RTTY now on-line)

[Jerry Pixton <jpixton@shentel.net>]

At 01:54 PM 10/2/2004 +0100, Ian White, G3SEK wrote:
> Jerry Pixton wrote:
> > Since the JPS NIR-12 filters were not available, last spring I opted for 
> > the MFJ 784B Audio DSP filters which I put in series from my radios, 
> > FT1000mp and IC756proII, to the sound cards. In spite of good filtering 
> > in both radios, the audio filters make a BIG difference. I have the audio 
> > filters set up with a 500 hz and a 250 hz position as well as a twin 
> > peaked position. With the hundreds of stations on 20 meters last week end 
> > I could search in the 250 hz position and generally seperate almost all 
> > stations. The occassional stations that were sitting almost on top of 
> > each other, I just put on the bandmap and moved on unless they were a 
> > multi. If they were 50 hz or so apart then the twin peak filter was 
> > useful. I would say that the audio filters made a big improvement in my 
> > station.
> Do the outboard DSP filters do anything that the radios' built-in DSP 
> filters and de-noisers cannot?


Absolutely!

As you recall some months ago I figured out how to get the best filtering 
out of my IC756proII by using the LSB-data filters instead of the RTTY 
filters. And the FT1000mp has a good set of filters.

But the outboard DSP filters have a much steeper slope that really enhances 
the audio that goes to the soundboard for MMTTY, etc to work with. Don 
pointed this out some time ago, and I bought one DSP unit to try, used it 
for one contest and immediately bought the second unit for the other radio. 
About half the time on a busy contest band, like 20 was the other day, I 
use the narrowest filters from the radios (250 hz) AND the 250 hz DSP rtty 
filter on the outboard unit.

BTW, I rarely use the DSP filtering in the FT1000mp - it never seems to do 
anything for rtty.

Jerry, W6IHG



> As far as I'm aware, the twin peak filter is the only feature mentioned 
> that the MP doesn't have at all (don't know about the Pro-II) but both 
> bandpass and twin-peak filtering are also available in MMTTY.
>
> Or do the outboard DSP boxes really perform so much better than the DSP 
> options in the radios and in MMTTY?
>
>
> --
> 73 from Ian G3SEK
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------------------------------------------
Dr. Jerry R. Pixton, PIXOS Designs LLC
http://www.pixos.com/designs/RadioTuner/
jpixton@shentel.net
------------------------------------------


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