Re: [K3] K3NA on 5 pole vs 8 pole filters

Posted by Bill W4ZV on May 27, 2010; 8:38pm
URL: http://elecraft.85.s1.nabble.com/K3-K3NA-on-5-pole-vs-8-pole-filters-tp5109906p5110460.html

Alfred Frugoli wrote

I remember reading a comparison by I think K3NA on the differences between 5
pole and 8 pole filters that eventually lead me to stick with the 5 pole
filters.

Eric and I are both ex-Orion users, which worked well with 4-pole filters so I concluded 5-poles would be sufficient in the K3.  After receiving my first K3 I discovered it had a much lower hardware AGC threshold. This led to the "HAGC mod" which was implemented around S/N 350, but I still don't think the threshold is as high as Orion's.  Therefore the steeper skirts in the 8-pole filters are necessary to prevent AGC pumping from close-in strong signals.  I've since switched from all 5-pole 500s to all 8-pole 500s (Inrads) in both of my units.  

I suspect the K3 could be improved without other harmful effects by raising the AGC threshold a little more.  Someday when I have nothing better to do I may try some experiments to see.  The DSP filters in both rigs are probably similar but the lower AGC threshold in the K3 makes it more susceptible to strong adjacent signals if you only use 5-pole filters.  However if you don't operate in extreme environments like 160 contests you may never notice any difference.

73,  Bill