[Elecraft] Filter confusion, K2

[Lyle Johnson]

Hello Ed!

> First, I have installed the DSP option in my K2. When I select XFIL, the
> bandwith now says 0.00. Is this supposed to be, or did I mess something
> up, and if so how do I fix it?

I don't understand this comment, so I'll let someone else handle it :-)

> Second, I wonder if one of our members could offer a short comment or
> two on the relationship among the various filters available,
> specifically the relationship between XFIL, AFIL, the DSP selected
> filters, and the filters on the SSB board. I don't understand how they
> interact. Does a DSP filter further filter an XFIL filter? I know that
> DSP is at the AF stage, as is AFIL, but is DSP active when AFIL filters
> are active?

The K2 has a variable bandwidth crystal filter at its IF of 4.9152 MHz.  You
set this up using CAL FIL to the widths you want.  If you have the KSB2
option, then there is an additional crystal filter available of about 2 kHz
bandwidth.

After the IF filter, the signal is amplified and then converted to audio in
the product detector.

AFIL is only available if you have either the KAF2 or the KDSP2 installed.
There is no "AFIL" built into the K2.

If you have the optional KAF2 installed, then there are up to two filters
available with the AFIL selection. These filters are after the product
detector and before the audio amplifier.

If you have the optional KDSP2 installed, then it provides a number of
selectable audio filters.  The DSP filters take the place of the filters in
the KAF2, and are selected by the AFIL button.  There are up to four
different filters per mode (CW, SSB and RTTY).

You set the DSP filters to suit your tastes and needs.  Various width
filters are useful under different band conditions and activity (heavy QRM,
quiet band with few signals, etc).  In addition, denoiser and notch
functions are available in the KDSP2 to further aid in signal reception
under varying conditions.

In summary, then, you have either the variable width IF filter or the SSB
filter at IF.  At audio you have no filtering, or the KAF2 filter, or the
DSP filter available, depending on the options in your radio.

73,

Lyle KK7P