[Elecraft] K3: 200Hz filter and manual notching oddity

[Dan Sherwood]

All,

I purchased 200 Hz 5-pole filters for my K3.  They work fine except for one
oddity:  If I set a manual notch at exactly 700 Hz, then sweep the bandwidth
control from the maximum of 2.5 KHz to a minimum 0.05 KHz, I would expect
the audio to disappear at whatever the notch width is, (Passband <= NOTCH),
and stay that way.  It does not.

My findings:

Between bandwidth settings 2.8 and 0.30 ­ full audio. (FL3 and FL4, 2.8K and
500Hz transitioning at 0.5)
Bandwidth 0.25 ­ abrupt total silence, FL4 (500Hz filter) (might have
expected this at 0.20 instead)
Bandwidth 0.20 ­ total silence, FL5(new 200Hz filter)
Bandwidth 0.15 ­ total silence, FL5
Bandwidth 0.10 ­ full audio abruptly returns, FL5 (unexpected)
Bandwidth 0.05 ­ full audio, FL5 (unexpected)

I would have expected audio suppression at 0.2 KHz and continuing down to
0.05 KHz, when the 200 Hz filter was switched in.  The fact the audio
resumed when the DSP setting was at 100 and 50 Hz was unexpected.  Granted,
I would not normally use a notch to separate signals but would tune either
high or low of the interfering signal, so this is not really a big deal.  I
do seem to find the most pleasing CW copy right at DSP bandwidth of 200 Hz
but not less.  Parameters: Band ­ 10 MHz CW main receiver, K3 F/W MCU
v04.51.

73,

Dan
W6DAS