[Elecraft] K3: Choosing which filters to buy

[Ed Muns]

> I think Doug has hit the nail on the head.  For casual CW, 
> just use the DSP.  If it isn't good enough, you can always 
> add the 500 Hz roofing filter later.

The take-away advice was to not add any additional filters until:

1.  You know what bandwidth(s) you will use a lot in each mode of interest,
AND
2.  You know that you have large signals near your operating frequency that
interfere with the DSP filtering.

Most of us seldom have condition 2, so the DSP filtering is completely
satisfactory with the 2.7 or 2.8 kHz roofing filter.  Unless one is very
sure about both points above, it makes much more sense to use the K3 for a
while until you have definitive answers before selecting protective roofing
filters.

> For more serious CW operating, I'm thinking the next filter 
> to get is the 1 KHz filter to give better 
> tuning-across-the-band performance.  My 3rd choice would then 
> be the ultra narrow (250?) filter.

As has been stated many times on this reflector, the 250 Hz 8-pole filter is
actually 370 Hz at the -6 dB points.  Review the filter plots on the
Elecraft web site.  If you already have a 400 (actually 435 Hz) or a 500
(about 520 Hz, I think), then the "250 Hz filter" is superfluous.  If you
need a narrow roofing filter for crowded 160 meter band conditions, then the
200 Hz 5-pole is an excellent complement to the 400 or 500 Hz roofer.

The only cases I see for the 250 Hz filter are:

A.  If you do NOT have a 400 or 500 Hz filter and want a slightly tighter
CW/RTTY filter, then 370 Hz (called "250 Hz") is great.
B.  If you are primarily interested in RTTY contesting with very crowded
band conditions, then the 370 is the tightest roofing filter now available
for the K3 that doesn't roll off the outside passband of a 170 Hz shift
tone-pair.  Even so, I often use 200 Hz DSP and tolerate the roll off in
exchange for attenuation of more of the pile-up.  When the variable crystal
filters come out, the 200-500 Hz (or whatever it turns out to be in that
range) will be another excellent alternative.

73,
Ed - W0YK