[Elecraft] K3 Roofing filters

[Gary W. Hvizdak]

On Tuesday August 6, Ivan (G3IZD) wrote ...

"I am about to purchase a K3 ... what is the general feeling regarding
[filter] bandwidth(s) ..."

--

Hi Ivan,

    In addition to the choices available from Elecraft and INRAD, WB2ART
and I also offer a 700 Hz (wide CW) alternative.  IMHO 700 Hz fits really
well between the INRAD 1.5 k Hz and 400 Hz filters and it's ideal for
scanning.

    The lead-time for the 700 Hz filter is upwards of 14 weeks, as there's
a 12-manufacturing lead-time and we only commission production as demand 
warrants.  The current batch (due to arrive in early October) will probably
sell out within a matter of hours.  The next batch can be expected sometime
between December and February.

--- - - - ---

    Our website – http://www.unpcbs.com/ – features a unique visual
comparison of the five 8-pole filters (1,000, 700, 500, 400, and 250 Hz).
This comparison is packaged as both an online slideshow and as a
(printable) PDF file.  Brief descriptions accompany each slide.  As a
whole, these descriptions create a concise 8-pole CW filter buyer's guide

    If you are a serious contester, then 700 and 400 Hz would be an
excellent choice.  Otherwise (if you're not a serious contester) then the
700 is probably the only CW filter you'll ever need.  Oh and it's also
ideal for 500 Hz digital formats.

--- - - - ---

    Additional suggestions ...

1)  Avoid filters whose widths are too similar.  Specifically, IMHO a ratio
of less than 1.4 (i.e. the square root of two) is an exercise in 
diminishing returns.

2)  For historic reasons, the filter widths are not always the same as
their designations.  This is especially true of the INRAD 250 Hz 8-pole
filter, which is closer 370 Hz wide.

3)  INRAD offers two additional 8-pole filters – 1500 Hz and 500 Hz – which
are not available through Elecraft.

4)  If you have the sub-RX, then adding/changing filters is a fairly
significant undertaking.  (Thus the advice about just getting a bare K3 and 
adding filters later may not apply to you, if your intention is to get a
factory assembled K3 with sub-RX.)

Cheers,
Gary  KI4GGX