K3 2.7kHz filter DSP FC

[Stewart Baker]

Can someone explain to me why with the standard 5 Pole 2.7 kHz
filter the DSP FC = 1.6kHz ?

Looking at the NORMed DSP for that filter the LO = 0.25 kHz and
the HI = 2.7 kHz.

So I would have thought that FC = (2.7 - 0.25) / 2 or 1.225 kHz
say 1.2 kHz.

Maybe my idea of what FC represents is wrong..

73
Stewart G3RXQ
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[Dave Hachadorian]

----- Original Message -----
From: "Stewart Baker" <[hidden email]>
To: "Elecraft Reflector" <[hidden email]>
Sent: Wednesday, March 19, 2008 11:35 AM
Subject: [Elecraft] K3 2.7kHz filter DSP FC


Can someone explain to me why with the standard 5 Pole 2.7
kHz
filter the DSP FC = 1.6kHz ?

Looking at the NORMed DSP for that filter the LO = 0.25 kHz
and
the HI = 2.7 kHz.

So I would have thought that FC = (2.7 - 0.25) / 2 or 1.225
kHz
say 1.2 kHz.

Maybe my idea of what FC represents is wrong..
----------------------------------
I don't have a radio, so I'm guessing at what all these
number mean, but I think that when you did the average it
should have been (2.7 + 0.25)/2 = 1.475

It's not all the way to 1.6, but closer.

Dave Hachadorian, K6LL
Yuma, AZ

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[Ed Muns, W0YK]

> Can someone explain to me why with the standard 5 Pole 2.7
> kHz
> filter the DSP FC = 1.6kHz ?
>
> Looking at the NORMed DSP for that filter the LO = 0.25 kHz
> and
> the HI = 2.7 kHz.
>
> So I would have thought that FC = (2.7 - 0.25) / 2 or 1.225
> kHz
> say 1.2 kHz.
>
> Maybe my idea of what FC represents is wrong..
> ----------------------------------
> I don't have a radio, so I'm guessing at what all these
> number mean, but I think that when you did the average it
> should have been (2.7 + 0.25)/2 = 1.475
>
> It's not all the way to 1.6, but closer.

The math is (2.7/2) + 0.25 = 1.60 because Fc, the center frequency of the
filter is half the filter bandwidth plus the frequency of the lower edge.

73,
Ed - W0YK

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[Stewart Baker]

Thanks to all who replied, particularly Ed.
I now see that I should add the LF edge rather than subtracting
it- obvious really DUH !

73
Stewart G3RXQ
On Wed, 19 Mar 2008 10:05:16 -0700, Ed Muns wrote:

>> Can someone explain to me why with the standard 5 Pole 2.7
>> kHz
>> filter the DSP FC = 1.6kHz ?
>>
>> Looking at the NORMed DSP for that filter the LO = 0.25 kHz
>> and
>> the HI = 2.7 kHz.
>>
>> So I would have thought that FC = (2.7 - 0.25) / 2 or 1.225
>> kHz
>> say 1.2 kHz.
>>
>> Maybe my idea of what FC represents is wrong..
>> ----------------------------------
>> I don't have a radio, so I'm guessing at what all these
>> number mean, but I think that when you did the average it
>> should have been (2.7 + 0.25)/2 = 1.475
>>
>> It's not all the way to 1.6, but closer.
>>
> The math is (2.7/2) + 0.25 = 1.60 because Fc, the center

frequency of the
> filter is half the filter bandwidth plus the frequency of the
lower edge.

>
> 73,
> Ed - W0YK
>
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