Filter Question

[Wilson Lamb]

Would someone please explain the relationship between our plug in filters (K3) and the variable filter response provided by our width control.
As I understand the situation, the plug in filters we buy are roofing filters, used to prevent intermod from strong signals outside the pass band.
Is there more to it?
If there were no other signals, would the width control work the same with and without the plug in filters?
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[Bill Frantz]

You understand it well.

The plug in filters work before the AtoD converter and protect
it from desense due to strong nearby signals. Desense occurs
when the ALC reduces receive sensitivity because of this strong
signal. This level of suppression can be useful with other hams
operating nearby, like a neighbor or a multi-radio operation
like field day with both CW and digital stations.

The width control works with the DSP filter to provide finer
control of the bandwidth. By narrowing the passband, you can
reduce the total band noise coming through the receiver and
improve the signal to noise ratio for the desired signal. You
can also use it to suppress a strong, slightly off frequency, signal.

Without other signals, the width control will work the same with
or without the plug in filters. The ifs/ands/and buts are that
if both filters are set to about the same width, the skirts will
be a bit sharper. (DSP filters tend to have very sharp skirts.)

73 Bill AE6JV

On 9/9/20 at 1:24 PM, [hidden email] (Wilson  Lamb) wrote:

>Would someone please explain the relationship between our plug
>in filters (K3) and the variable filter response provided by
>our width control.
>As I understand the situation, the plug in filters we buy are
>roofing filters, used to prevent intermod from strong signals
>outside the pass band.
>Is there more to it?
>If there were no other signals, would the width control work
>the same with and without the plug in filters?
-----------------------------------------------------------------------
Bill Frantz        | Truth and love must prevail  | Periwinkle
[phone]      | over lies and hate.          | 150
Rivermead Rd #235
www.pwpconsult.com |               - Vaclav Havel |
Peterborough, NH 03458

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[Jim Brown-10]

Hi Wilson,

The response of the DSP IF filters combines (cascades) with the roofing
filters; when both are the same bandwidth, their skirts fall off much
more sharply (the rolloff is equal to the sum of the two filters). When
one is much broader than the other, we get only the skirts of the
narrowest one.

This is generally true of all filters, whether digital or analog, except
to the extent that the combined phase shift modifies the total response.

73, Jim K9YC

On 9/9/2020 10:24 AM, Wilson Lamb wrote:
> Would someone please explain the relationship between our plug in filters (K3) and the variable filter response provided by our width control.
> As I understand the situation, the plug in filters we buy are roofing filters, used to prevent intermod from strong signals outside the pass band.
> Is there more to it?

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