[Elecraft] Filter Selection Approach

[Bill W4ZV]

That is a lot of filters ... 

2) Unless you are in very heavy QRM/pile-up situations the 
   roofing filter does not provide a lot of "value added" 
   since the final bandwidth is determined by the DSP.  The 
   1 KHz filters add little benefit vs. the 1.8 KHz or 1.5 
   KHz filters.  



I would disagree regarding the value or benefit of the 1 KHz filter.
Originally I had, for CW, 1800, 500 & 200 filters.  Since I normally set the width to 700 Hz for normal non contest CW operating, it seemed that I was having problems with loud signals within about 900 to 1800 HZ hitting the AGC.  So when a 1000 HZ filter became available to trade for my 1800 HZ filter I jumped on it and have not looked back!


I was the one who traded my 1.0 for Hank's 1.8.  The reason I didn't like the 1.0 is the following, which depends on the PITCH you normally like to use.  If you use a high pitch, this may not apply, but I like a low pitch of 300-350 for weak signal DX-ing (and 400-450 for contesting).

The way the K3 works is that XFILs are normally centered about the selected PITCH, **UNLESS** the lower end of that passband falls below 200 Hz.  In that case, the firmware shifts the XFIL such that the lower end is 200 Hz (to prevent negative IF response).  If I set my PITCH to 300, my passband is actually 200-1200, or 900 Hz above my zero beat pitch.  This means my AGC would still be pumped by a signal ~1 kHz away (actual 6 dB BW is 1063 Hz per the Elecraft/Inrad plot).  In most rigs (e.g. Orion) with a 1 kHz filter centered on the desired PITCH, you would only be susceptible to AGC pumping ~500 Hz away.  Practically speaking, for my desired low pitch of 300 Hz, the 1.0 filter in the K3 acts more like a much wider filter in another rig since it's passing signals ~1 kHz above my 300 Hz PITCH.  

For casual use a 1.0 may be OK, but where I live in the land of Elephants and Fleas (160m), the 1.0 is practically worthless if there is much activity on the band.  I swapped my 1.0 because of this and because I felt the 1.8 might be useful for SSB contesting (when and if 10m ever comes back).

73,  Bill

P.S.  I've still never understood why Orion worked with its XFILs centered at low pitches...yet the K3 apparently has a problem.



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