[Elecraft] Planning the next filters

[Joe Subich, W4TV]

 > I plan on a 250 Hz CW filter,

I may be the odd man out but I can't see much enough difference between
the "400 Hz" (450 Hz @ -6dB) and the "250 Hz" (370 Hz @ -6dB) to justify
the cost.  If you feel you *need* a narrower filter in the 8215 KHz IF,
consider the new KFL3C-200 which is truly 200 Hz wide at -6 dB.
See: <http://www.elecraft.com/K3/K3_filter_plots.htm> particularly the
last graph.

> but am going back and forth between the 2.1 and 1.8 kHz filters.

My choice - after trying the 1.5 KHz filters from INRAD and working with
both 2.1 KHz and 1.8 KHz DSP bandwidths (with center frequency offset to
maintain the low frequency cutoff at 100 - 250 Hz) was the 2.1 KHz
filter.  I felt the DSP provided sufficient high frequency roll off
if/when it was needed but the 2.1 KHz filter provided more flexibility -
and I ended up using 2.4 KHz - with the 2.1 KHz "roofing" filter set to
kick in at 2.4 KHz - as my "normal" SSB bandwidth.

While amateur activity is not channelized, most day-to day SSB activity
seems to fall on 3 KHz boundaries with occasional 2.5 KHz "steps".  Even
in a busy contest, things don't tend to get closer than 2 KHz as long as
the stations can "hear".  Most of the QRM on SSB isn't necessarily from
overlapping signals ... it's from transmit phase noise and IMD.  That's
not something that *any* receiver filter can deal with as those are
"spurious" signals outside the "necessary bandwidth" generated and
radiated by the transmitting (interfering) station.

73,

    ... Joe, W4TV


On 3/8/2018 11:22 AM, Chuck Chandler wrote:
> Right now I have the stock SSB and a 400 Hz filter in both main and sub
> rcvrs.  I would like to add some a few at a time.  My first priority is to
> add a couple to the main receiver, since it is the biggest chore to get
> to.
> 
> I plan on a 250 Hz CW filter, but am going back and forth between the 2.1
> and 1.8 kHz filters.  I know that narrowing the DSP to 1.8 gives a really
> difficult to understand voice signal, while the 2.1 allows in more adjacent
> signals.  However, the roofing filters may not behave in the same manner.
> For example, the 1.8 could be set to turn on at 2.1 to take advantage of
> skirt shape.
> 
> I primarily DX, and operate in some contests as well.  I know SSB contests
> really need a narrow SSB filter.
> 
> Any suggestions on the matter from those who have gone this route before?
> 
> 73 de Chuck, WS1L
>