K3 5 pole vs 8 pole filters - attenuation in the passband

[lstavenhagen]

Hi all,
Quick question - do the 8 pole roofing filters have more attenuation, as a general rule, in their passbands than the 5 pole? Long story on how I arrived at this question in terms of troubleshooting something I've noticed in my K3 and K3S, but I'm just curious if there's supposed to be a noticeable difference?

My assumption is the 8 poles are going to have a little more attenuation than the 5's, perhaps by as much as 3 db or more. Is that the case that ya'll have noted?

I've looked through the list archives and haven't found a prior discussion of this, so just wondering.

Thanks es 73,
LS
W5QD

[Jim Brown-10]

On Fri,2/26/2016 8:50 AM, lstavenhagen wrote:
> Quick question - do the 8 pole roofing filters have more attenuation, as a
> general rule, in their passbands than the 5 pole?

Yes, but the difference doesn't matter -- it's in the IF, not the front
end. Further, there is an menu adjustment for each filter to equalize
the IF gain when switching between filters.

The advantage of 8-pole filters is smoother response in the passband of
wider filters, and steeper skirts. In general, roofing filters are only
needed for high QRM conditions like contesting. Their function is to
protect the DSP from overload by strong signals outside the desired
passband.  When the DSP IF is set to a bandwidth close to that of the
roofing filter, the two filters cascade to provide even steeper skirts.
Again, needed only under contest conditions.

It's amazing the things one can learn by reading the manual. :)

73, Jim K9YC
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[lstavenhagen]

Well, yes, to spill the beans on this: it was when I was reviewing the filter gains on my K3 the other day that this came up. I built my K3 with the stock 2.7khz 5 pole filter in FL1 and an 8 pole 400hz in FL2 - however, to even out FL1 and FL2 requires the gain to be nearly maxed out for FL2 (8 db gain, IIRC). My K3S, however, has 8 pole 2.8khz and 400hz in goth FL1 and 2, respectively. But they're almost dead even in terms of attenuation with FL2 set at only 2 db gain.

So that led me to wonder if the 5 pole in my K3 had less attenuation in general, accounting for the difference. Just a curiosity for me.

73,
LS
W5QD

[Gary Smith-2]

Interesting timing for this thread. A friend wants to buy my K3 and
fit it with the most advantageous filters for his contesting methods.

I remember when selecting filters back in 2009, the consensus was the
8 pole 250 Hz filter was more desirable than the 5 pole 200 Hz
filter. Now its 7 years from back then, I don't know what is the
current consensus. I bought the 8 pole 250 for the main & Sub Rx
boards.

Which filter between the 5 pole 200 & 8 pole 250 Hz filter is
currently the most desirable for contesting conditions?

Thanks & 73,

Gary
KA1J


Hi all,
Quick question - do the 8 pole roofing filters have more attenuation,

as a
general rule, in their passbands than the 5 pole? Long story on how I
arrived at this question in terms of troubleshooting something I've
noticed
in my K3 and K3S, but I'm just curious if there's supposed to be a
noticeable difference?

My assumption is the 8 poles are going to have a little more
attenuation
than the 5's, perhaps by as much as 3 db or more. Is that the case
that
ya'll have noted?

I've looked through the list archives and haven't found a prior
discussion
of this, so just wondering.

Thanks es 73,
LS
W5QD



--
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uation-in-the-passband-tp7614635.html
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[Nr4c]

Well, no longer a question. The 5 pole 200 is no longer available.

Sent from my iPhone
...nr4c. bill

> On Feb 26, 2016, at 5:03 PM, Gary Smith <[hidden email]> wrote:
>
> Interesting timing for this thread. A friend wants to buy my K3 and
> fit it with the most advantageous filters for his contesting methods.
>
> I remember when selecting filters back in 2009, the consensus was the
> 8 pole 250 Hz filter was more desirable than the 5 pole 200 Hz
> filter. Now its 7 years from back then, I don't know what is the
> current consensus. I bought the 8 pole 250 for the main & Sub Rx
> boards.
>
> Which filter between the 5 pole 200 & 8 pole 250 Hz filter is
> currently the most desirable for contesting conditions?
>
> Thanks & 73,
>
> Gary
> KA1J
>
>
> Hi all,
> Quick question - do the 8 pole roofing filters have more attenuation,
>
> as a
> general rule, in their passbands than the 5 pole? Long story on how I
> arrived at this question in terms of troubleshooting something I've
> noticed
> in my K3 and K3S, but I'm just curious if there's supposed to be a
> noticeable difference?
>
> My assumption is the 8 poles are going to have a little more
> attenuation
> than the 5's, perhaps by as much as 3 db or more. Is that the case
> that
> ya'll have noted?
>
> I've looked through the list archives and haven't found a prior
> discussion
> of this, so just wondering.
>
> Thanks es 73,
> LS
> W5QD
>
>
>
> --
> View this message in context:
> http://elecraft.365791.n2.nabble.com/K3-5-pole-vs-8-pole-filters-atten
> uation-in-the-passband-tp7614635.html
> Sent from the Elecraft mailing list archive at Nabble.com.
> ______________________________________________________________
> Elecraft mailing list
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>
>
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[lstavenhagen]

for what it may be worth, the 400hz 8 poles in my K3 and K3S are like brick walls. I haven't yet found a situation where the 400hz filter plus using the DSP to go narrower hasn't covered even the most crowded situations.

I'm 99.9986% CW, so that filter is adequate for me but if you're a PSK hound, for example, I could see the 250hz filter. For RTTY, I think the 250hz filter might be borderline, though...

Just my thoughts,
LS
W5QD

[K9MA]

I have both the 8 pole 400 Hz and 250 Hz filters.  For CW, I just
haven't found the 250 Hz filter that useful.  For one thing, it's not
really that much narrower than the 400 Hz filter.  I do find that a
bandwidth less than 400 Hz is sometimes useful in heavy QRM, but I think
the 400 Hz filter and DSP would be adequate.  If I were to do it over
again, I would not buy the 250 Hz filter, at least not before trying
without in a few contests.

73,

Scott  K9MA

On 2/27/2016 09:56, lstavenhagen wrote:

> for what it may be worth, the 400hz 8 poles in my K3 and K3S are like brick
> walls. I haven't yet found a situation where the 400hz filter plus using the
> DSP to go narrower hasn't covered even the most crowded situations.
>
> I'm 99.9986% CW, so that filter is adequate for me but if you're a PSK
> hound, for example, I could see the 250hz filter. For RTTY, I think the
> 250hz filter might be borderline, though...
>
> Just my thoughts,
> LS
> W5QD
>
>
>
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/K3-5-pole-vs-8-pole-filters-attenuation-in-the-passband-tp7614635p7614671.html
> Sent from the Elecraft mailing list archive at Nabble.com.
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--
Scott Ellington  K9MA
Madison, Wisconsin, USA

[hidden email]

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[jeff stai-2]

On Sat, Feb 27, 2016 at 7:56 AM, lstavenhagen <[hidden email]>
wrote:

> I'm 99.9986% CW, so that filter is adequate for me but if you're a PSK
> hound, for example, I could see the 250hz filter. For RTTY, I think the
> 250hz filter might be borderline, though...
>

For RTTY the sweet spot is 400. At 250 you might lose information your
decoders need to work. 73 jeff wk6i


--
Jeff Stai ~ [hidden email]
Twisted Oak Winery ~ http://www.twistedoak.com/
Facebook ~ http://www.facebook.com/twistedoak
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[Richard Ferch]

My solution for this is to configure the K3 to switch the 250 Hz roofing
filter in at 350 Hz. A DSP filter of 250 Hz is a bit narrow, but with a
350 Hz DSP setting and the 250 Hz roofing filter, I still get good copy.

That being said, most of the time I operate RTTY with a 500 Hz roofing
filter and the DSP filter at 400-450 Hz; I only use the 350 Hz setting
when there is a strong signal shoulder-to-shoulder with the one I am
trying to copy.

73,
Rich VE3KI

WK6I wrote:

> For RTTY the sweet spot is 400. At 250 you might lose information your
> decoders need to work. 73 jeff wk6i

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[Joe Subich, W4TV-4]

The Elecraft/Inrad "250 Hz" filter is actually 370 Hz at -6dB where the
"400 Hz" filter is 435 Hz.  That's not enough to make a real difference
*as a roofing filter* since the primary selectivity of the K3/K3S is in
the DSP.

370 Hz is the minimum necessary bandwidth for a 170 Hz shift 45.45 baud
FSK signal ... any tighter than that and the loss of sideband energy
creates increased inter symbol interference (one bit gets "smeared" in
to the next).  The 400 Hz filter is really the one to have for RTTY -
even if the DSP is tightened below that on occasion.

It is a shame the Elecraft 200 Hz filters are no longer available -
they were superior overall for very tight CW (tighter than the 250 Hz,
8 pole filters all the way to -40 or - 50 dB) and provided a real
difference from the 400 Hz filters.  If one really *must* have the
250/370 Hz filter, the next filter to have would be the Elecraft/Inrad
1000/1060 Hz, the custom UnPCBS <http://www.unpcbs.com/> 700/785 Hz
filter, or perhaps the Inrad 500/550? Hz 8 pole filter (although the
difference between the "250" and "500" is rather small but not as
small as between the 250 and 400 nominal filters).

Remember, the purpose of the first IF ("roofing") filter is to protect
the If and Analog to Digital converter (ADC) from strong, adjacent
signals, *not* to provide the final selectivity as in the case of a
conventional superhetrodyne receiver.

73,

    ... Joe, W4TV


On 2/27/2016 11:21 AM, Jeff Stai wrote:

> On Sat, Feb 27, 2016 at 7:56 AM, lstavenhagen <[hidden email]>
> wrote:
>
>> I'm 99.9986% CW, so that filter is adequate for me but if you're a PSK
>> hound, for example, I could see the 250hz filter. For RTTY, I think the
>> 250hz filter might be borderline, though...
>>
>
> For RTTY the sweet spot is 400. At 250 you might lose information your
> decoders need to work. 73 jeff wk6i
>
>

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[Guy Olinger K2AV]

I find that the biggest use for the "250" filter, which really is ~350, is
to narrow a run station passband when the band gets crowded. These days
that's almost always. I find a place where the "400" really 450, does not
contain other stations, and then operate at 350 Hz bandwidth. I use the
"400" at 450 for casual CW operation. Have to remember that the 250 filter
is the filter that INRAD designed for use in the FT1000MP series, as part
of a cascaded PAIR of filters where the pair was a top shelf 250. The pair
was the 8 MHz IF and 455 kHz IF filters in series.

The "250" 8 pole and the DSP set at 250 work very well together, good
enough for any of my needs. With the "250" defined as 350 in the K3, and
the DSP at 350, you have very sharp skirts eminently useful for crowded
contest work.

73, Guy K2AV

On Sat, Feb 27, 2016 at 11:21 AM, Scott Ellington <[hidden email]>
wrote:

> I have both the 8 pole 400 Hz and 250 Hz filters.  For CW, I just haven't
> found the 250 Hz filter that useful.  For one thing, it's not really that
> much narrower than the 400 Hz filter.  I do find that a bandwidth less than
> 400 Hz is sometimes useful in heavy QRM, but I think the 400 Hz filter and
> DSP would be adequate.  If I were to do it over again, I would not buy the
> 250 Hz filter, at least not before trying without in a few contests.
>
> 73,
>
> Scott  K9MA
>
> On 2/27/2016 09:56, lstavenhagen wrote:
>
>> for what it may be worth, the 400hz 8 poles in my K3 and K3S are like
>> brick
>> walls. I haven't yet found a situation where the 400hz filter plus using
>> the
>> DSP to go narrower hasn't covered even the most crowded situations.
>>
>> I'm 99.9986% CW, so that filter is adequate for me but if you're a PSK
>> hound, for example, I could see the 250hz filter. For RTTY, I think the
>> 250hz filter might be borderline, though...
>>
>> Just my thoughts,
>> LS
>> W5QD
>>
>>
>>
>> --
>> View this message in context:
>> http://elecraft.365791.n2.nabble.com/K3-5-pole-vs-8-pole-filters-attenuation-in-the-passband-tp7614635p7614671.html
>> Sent from the Elecraft mailing list archive at Nabble.com.
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>> Message delivered to [hidden email]
>>
>
>
> --
> Scott Ellington  K9MA
> Madison, Wisconsin, USA
>
> [hidden email]
>
>
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[Jim Brown-10]

On Sat,2/27/2016 9:33 AM, Richard Ferch wrote:
> My solution for this is to configure the K3 to switch the 250 Hz
> roofing filter in at 350 Hz. A DSP filter of 250 Hz is a bit narrow,
> but with a 350 Hz DSP setting and the 250 Hz roofing filter, I still
> get good copy.

WK6I wins RTTY contests. I'd go with his advice that 400 Hz is right for
RTTY. He's not the only one who thinks so. So do W0YK (another winning
RTTY contester) and G3YYD, the author of 2Tone, an excellent RTTY
decoder. Switch to narrower IF only when the QRM gets really bad.

And so do I.  FWIW, I was saying that before anyone. :)

73, Jim K9YC
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