[K3] K3NA on 5 pole vs 8 pole filters

[Alfred Frugoli]

Fellow Elecrafters,

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.  Does anybody know what I'm thinking of, because Google searches,
and Nabble searches of the Elecraft archives aren't turning anything up, and
I've gotten no response from direct contact with K3NA (maybe I have an old
e-mail).

73 de Al, KE1FO

K3 #3055
K3 #4094
-----
Check out my Amateur Radio Contesting blog at ke1fo.wordpress.com.
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[Bill W4ZV]

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

[wc1m]

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.

73, Dick WC1M

-----Original Message-----
From: Bill W4ZV [mailto:[hidden email]]
Sent: Thursday, May 27, 2010 4:39 PM
To: [hidden email]
Subject: Re: [Elecraft] [K3] K3NA on 5 pole vs 8 pole filters



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
--
View this message in context:
http://elecraft.365791.n2.nabble.com/K3-K3NA-on-5-pole-vs-8-pole-filters-tp5
109906p5110460.html
Sent from the Elecraft mailing list archive at Nabble.com.


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[Ed Muns, W0YK]

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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[Bill W4ZV]

Ed Muns, W0YK wrote

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

True but "AGC Off" only applies to the digital (DSP) AGC.  Hardware AGC is always on (to protect the DSP) and therefore is subject to blocking, even if AGC is set to Off.

73,  Bill

[Ed Muns, W0YK]

> Ed Muns, W0YK wrote:
> >
> > Keep in mind that Eric (K3NA) typically operates with AGC off,
> > especially in the presence of strong signals.
> >

Bill Tippett, W4ZV, replied:
>
> True but "AGC Off" only applies to the digital (DSP) AGC.  
> Hardware AGC is always on (to protect the DSP) and therefore is
> subject to blocking, even if AGC is set to Off.

Ah, right ... fuzzy thinking.  Radio Expeditions, Inc. may have a lot of
5-pole filters to swap out before the next trip, hi!

Ed - W0YK

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[Eric Scace K3NA]

Gents --

   I am not sure where the misinformation began that I use 5-pole
filters.  None of the K3s used by Radio Expeditions, and none of my
personal K3 radios, use 5-pole filters (other than the stock filter).

   My personal filter configuration at the time I bought my radios was:
2.7 kHz stock -- TX
1.8 kHz 8-pole -- forced for all SSB receive (even if DSP is wider), CW,
RTTY
1.0 kHz 8-pole -- CW, RTTY
0.4 kHz 8-pole -- CW, RTTY

   Radio Expeditions also includes 0.25 kHz 8-pole filters to aid in
searching for weak signals between strong ones in pileups; e.g., for
Ducie Island, when the band was open to Europe and we were trying to
find the weak Europeans in between louder signals calling from North
America.

   It is true that I run with AGC=off.  I have yet to find a combination
of AGC settings that sounds as clear as AGC=off.  This strategy isn't
for everyone and requires some care and discipline.
   -- I rarely do "casual listening" where AGC might even out signal
levels for comfortable speaker monitoring.
   -- I work hard for a very quiet listening environment, so that I can
hear 80+ dB of signal dynamic range.  With my headphones on, my noise
floor is the sound of my own heartbeat and the blood pulsing in my ears,
and I adjust the receiver so that the band noise is just above this level.
   -- I have an attenuator between my in-ear monitors and the radio
headphone jack.  The K3 audio output amplifier can not deliver a loud
enough signal into my in-ear monitors to make me go "ouch".

   The reward of this approach is an extraordinary clarity to signals,
and no residual gain reductions caused by static crashes or loud signals
hanging the AGC.

   [Bill W4ZV is correct: there is still gain control in front of the
A/D converter that cannot be disabled.]

73,
   -- Eric K3NA

on 2010 May 28 15:23 Ed Muns said the following:

>> Ed Muns, W0YK wrote:
>>    
>>> Keep in mind that Eric (K3NA) typically operates with AGC off,
>>> especially in the presence of strong signals.
>>>
>>>      
>
> Bill Tippett, W4ZV, replied:
>  
>> True but "AGC Off" only applies to the digital (DSP) AGC.  
>> Hardware AGC is always on (to protect the DSP) and therefore is
>> subject to blocking, even if AGC is set to Off.
>>    
>
> Ah, right ... fuzzy thinking.  Radio Expeditions, Inc. may have a lot of
> 5-pole filters to swap out before the next trip, hi!
>
> Ed - W0YK
>  

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