Difference between "real" filters (FL1 thru FL4) and DSP filters (SF1 thru SF4)

[John Wiener]

I have been playing with the KDSP2 on my K2 and was wondering if the  
DSP filters are significantly different in their effects than the  
effects of filters FL1 thru FL4.
To me, they seem a bit redundant, in terms of audio effect on listening.

Noise reduction is remarkable when activated...still learning how to  
use it for SSB, however.
I haven't seen the effects of the notch filter yet...is that supposed  
to eliminate adjacent carriers?

John
AB8O
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[Steven Pituch]

Hi John,
The DSP is audio.  Its got a sharper cutoff but can be affected by the AGC
which is also audio.  The crystals filters FL1 -FL4 are IF and closer to the
front end and cut interference before the AGC.

Yes, in non critical situations, the DSP filters are sharper, but if a loud
adjacent signal gets through the IF because a narrow IF filter is not being
used it will activate the AGC and desense the signal you are listening to.

The best thing to do is narrow it down first with the IF filters, and then
use the DSP narrow bandwidths if the IF filtering is not enough.

I have some samples of the bandwidths here.
http://users.ev1.net/~spituch/Steve's%20Page/Radio/RTTY/RTTY.html
By the way, using MixW to align the filters was very easy.

Regards,
Steve, W2mY/5

-----Original Message-----
On Behalf Of John Wiener
I have been playing with the KDSP2 on my K2 and was wondering if the DSP
filters are significantly different in their effects than the effects of
filters FL1 thru FL4.
To me, they seem a bit redundant, in terms of audio effect on listening.

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[Ron D'Eau Claire-2]

Steve, W2MY/5 wrote:

The DSP is audio.  Its got a sharper cutoff but can be affected by the AGC
which is also audio.  The crystals filters FL1 -FL4 are IF and closer to the
front end and cut interference before the AGC.

---------------------------------------------

The K2 AGC is not audio AGC. It's derived from RF in a separate I.F. strip
dedicated to producing an AGC voltage based on the strength of the signal at
the I.F. and the AGC voltage controls the gain of the I.F. amplifier. The
AGC circuits are on the control board. NE602 mixer U1 converts the I.F.
signal to about 150 kHz. That way any BFO signal at 4.9 MHz can't get into
the AGC system. The output of the NE602 is rectified to produce the DC AGC
voltage that operates the "S" meter and which controls the gain of the
MC1350 I.F. amplifier (U12) on the RF board.

Ron AC7AC

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[k6dgw]

While a "still wet behind the ears" student several hundred years ago, a
professor told me that "The best filters for any receiver are at the
antenna terminals, before any RF enters the receiver.  Once you let it
in, it's hard to control.  Unfortunately, filters are a bit hard to
implement that way, hence the superhetrodyne."

Fred K6DGW
Auburn CA CM98lw

Steven Pituch wrote:

> Hi John,
> The DSP is audio.  Its got a sharper cutoff but can be affected by the AGC
> which is also audio.  The crystals filters FL1 -FL4 are IF and closer to the
> front end and cut interference before the AGC.
>
> Yes, in non critical situations, the DSP filters are sharper, but if a loud
> adjacent signal gets through the IF because a narrow IF filter is not being
> used it will activate the AGC and desense the signal you are listening to.
>
> The best thing to do is narrow it down first with the IF filters, and then
> use the DSP narrow bandwidths if the IF filtering is not enough.
>
> I have some samples of the bandwidths here.
> http://users.ev1.net/~spituch/Steve's%20Page/Radio/RTTY/RTTY.html
> By the way, using MixW to align the filters was very easy.
>
> Regards,
> Steve, W2mY/5

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[Steven Pituch]

Sorry for the confusion.  Ron Is correct.  I just had a mental lapse there.
Steve, W2MY

Ron said:

The K2 AGC is not audio AGC. It's derived from RF in a separate I.F. strip
dedicated to producing an AGC voltage based on the strength of the signal at
the I.F. and the AGC voltage controls the gain of the I.F. amplifier. The
AGC circuits are on the control board. NE602 mixer U1 converts the I.F.
signal to about 150 kHz. That way any BFO signal at 4.9 MHz can't get into
the AGC system. The output of the NE602 is rectified to produce the DC AGC
voltage that operates the "S" meter and which controls the gain of the
MC1350 I.F. amplifier (U12) on the RF board.

Ron AC7AC

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