[Elecraft] 1 Khz filter

[Victor Rosenthal 4X6GP]

I am a CW operator and I have 2.8kHz, 1kHz, 400Hz and 200Hz filters in 
my K3. I think this is serious overkill (especially since I have another 
similar set in the subreceiver).

The function of the crystal filters is to allow you to operate closer 
than (roughly) the filter bandwidth to a signal that is S9+20 dB or more 
without the interfering signal having any effect on the desired signal. 
The continuously adjustable DSP filter is a brick wall for undesired 
signals weaker than that. But stronger signals can activate the hardware 
AGC in the K3 or K3S and cause desensitization even though the QRM is 
outside the DSP bandpass.

The optimum situation is to have a filter whose bandwidth is close to or 
slightly wider than the DSP bandwidth that you are using. So if you 
often operate with the DSP bandwidth set to, say, 900Hz, having a 1kHz 
filter would be convenient. If you only had the stock 2.7 kHz filter, 
then an undesired S9+20 dB signal 1 kHz away from the signal you are 
listening to might cause the sensitivity of the receiver to vary and 
thus interfere with your ability to copy, even though you wouldn't hear 
the interfering signal.

So it depends on your operating habits. Since I am in the habit of 
listening to CW with the DSP set to 400Hz or below, the 1kHz filter 
doesn't do anything for me. I also think the value of the 200 Hz filter 
is marginal, although it has been helpful at times (like when a 
super-strong station one hop away from me is trying to deliberately QRM 
a DX station but is not exactly on the DX frequency).

73,
Victor, 4X6GP
Rehovot, Israel
Formerly K2VCO
http://www.qsl.net/k2vco/
On 25 Jul 2017 22:49, john at kk9a.com wrote:
> What is this used for?
> 
> John KK9A
> 
> From: Ralph Matheny K8RYU
> Mon Jul 24 16:30:29 EDT 2017
> 
> 
> Anybody got a 1 Khz filter for K3 they wanna sell??
> 
> de K8RYU