[Elecraft] [K3] K3NA on 5 pole vs 8 pole filters

[Ed Muns]

Keep in mind that Eric (K3NA) typically operates with AGC off, especially in
the presence of strong signals.

Ed - W0YK
----------------------------------------
Ed Muns
Muns Vineyard - www.munsvineyard.com 
Facebook - www.facebook.com/munsvineyard 

Dick, WC1M, wrote:
>
> I had exactly the same experience as Bill (and I'm an ex-Orion user as
> well.) While Eric is correct that, in theory, roofing filters 
> with tights skirts aren't necessary in a down-conversion 
> design, the K3's hardware AGC threshold requires tighter 
> roofing filters when the band is crowded with loud signals. I 
> had the 5-pole 500 Hz filters, but quickly found that HAGC 
> pumping was a real problem in big CW contests. I was 
> routinely bothered by loud stations just above my passband 
> (using CW NOR). I subsequently replaced the 5-pole filters 
> with 8-pole 400 Hz filters and the problem pretty-much 
> disappeared. Like Bill, I think the HAGC threshold is still a 
> bit too low.

> 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. 
> > 

Bill, W4ZV, wrote:
>
> 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.