Re: [K3] K3NA on 5 pole vs 8 pole filters
Posted by
Ed Muns, W0YK on
May 28, 2010; 6:06pm
URL: http://elecraft.85.s1.nabble.com/K3-K3NA-on-5-pole-vs-8-pole-filters-tp5109906p5114108.html
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.
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