[K2] Filters attenuation

[Petr, OK1RP/M0SIS]

Hi,

I would like to ask for help. My K2 #4800 works fine but I realized the narrower filters have attenuation. I pre-set FL1>200Hz, FL2>400Hz and FL3>700Hz but with FL1 I recognised too much attenuation which degrading the reception of weaks sigs. Is there something which I am doing wrong please?

73 - Petr, OK1RP

[Dave-7]

I dunno about the loss you are seeing but I've measured about 8 dB of
loss in my K2 at 200 Hz vs 1 kHz BW. That does strike me a quite a bit
of loss. I just don't use the narrow filters often. I know of at least
one other K2 that has similar loss. Anyone else?


73 de dave
ab9ca/4





On 11/4/10 11:48 AM, ok1rp wrote:
>
> Hi,
>
> I would like to ask for help. My K2 #4800 works fine but I realized the
> narrower filters have attenuation. I pre-set FL1>200Hz, FL2>400Hz and
> FL3>700Hz but with FL1 I recognised too much attenuation which degrading the
> reception of weaks sigs. Is there something which I am doing wrong please?
>
> 73 - Petr, OK1RP
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[Petr, OK1RP/M0SIS]

Dave,

yes I am confirming > it is the attenuation which I am talking about...
When I am decreasing BW from 1.5k to 700Hz there is not noticeable att
(which means it's aprox. less then 3dB) but by going to 400Hz or even to
200Hz I hear big att which can be like You said 8dB or so.

Anybody else has similar experiences pls?

73 - Petr, OK1RP

On Thu, 04 Nov 2010 13:12:46 -0500, "dave" <[hidden email]> said:

> I dunno about the loss you are seeing but I've measured about 8 dB of
> loss in my K2 at 200 Hz vs 1 kHz BW. That does strike me a quite a bit
> of loss. I just don't use the narrow filters often. I know of at least
> one other K2 that has similar loss. Anyone else?
>
>
> 73 de dave
> ab9ca/4
>
>
>
>
>
> On 11/4/10 11:48 AM, ok1rp wrote:
> >
> > Hi,
> >
> > I would like to ask for help. My K2 #4800 works fine but I realized the
> > narrower filters have attenuation. I pre-set FL1>200Hz, FL2>400Hz and
> > FL3>700Hz but with FL1 I recognised too much attenuation which degrading the
> > reception of weaks sigs. Is there something which I am doing wrong please?
> >
> > 73 - Petr, OK1RP

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[Curt]

Yes, mine attenuates but haven't bothered to measure it.  Strangely, the 700
Hz seems worse than the narrower filters.

Curt KB5JO

>I dunno about the loss you are seeing but I've measured about 8 dB of
>loss in my K2 at 200 Hz vs 1 kHz BW. That does strike me a quite a bit
>of loss. I just don't use the narrow filters often. I know of at least
>one other K2 that has similar loss. Anyone else?

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[w2bvh]

  Petr,

I measured mine at 500 Hz a few years ago but never wrote down the
number. I do remember being surprised at how much it was.  I use a wider
filter most of the time and only go to the narrowest when there is
substantial qrm in the passband; for just the reason you mention.

73,
Lenny W2BVH
K2 sn 1520


On 11/4/2010 4:27 PM, Petr Ourednik wrote:

> Dave,
>
> yes I am confirming>  it is the attenuation which I am talking about...
> When I am decreasing BW from 1.5k to 700Hz there is not noticeable att
> (which means it's aprox. less then 3dB) but by going to 400Hz or even to
> 200Hz I hear big att which can be like You said 8dB or so.
>
> Anybody else has similar experiences pls?
>
> 73 - Petr, OK1RP
>
> On Thu, 04 Nov 2010 13:12:46 -0500, "dave"<[hidden email]>  said:
>> I dunno about the loss you are seeing but I've measured about 8 dB of
>> loss in my K2 at 200 Hz vs 1 kHz BW. That does strike me a quite a bit
>> of loss. I just don't use the narrow filters often. I know of at least
>> one other K2 that has similar loss. Anyone else?
>>
>>
>> 73 de dave
>> ab9ca/4
>>
>>
>>
>>
>>
>> On 11/4/10 11:48 AM, ok1rp wrote:
>>> Hi,
>>>
>>> I would like to ask for help. My K2 #4800 works fine but I realized the
>>> narrower filters have attenuation. I pre-set FL1>200Hz, FL2>400Hz and
>>> FL3>700Hz but with FL1 I recognised too much attenuation which degrading the
>>> reception of weaks sigs. Is there something which I am doing wrong please?
>>>
>>> 73 - Petr, OK1RP
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>

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[Don Wilhelm-4]

  Dave,

I am wondering if you have some problem with the crystals in the
variable IF filter.
The variable filter design point is near 500 Hz.  It will normally have
attenuation below 200 Hz width and the passband will bet more 'ragged'
above 1 kHz.  What I am saying is that you should have a constant filter
response at 700 Hz, 400 Hz with perhaps a small bit of attenuation at
200 Hz.  Below that width, attenuation will increase rapidly.

If your K2 is below SN 2560, and it has not been upgraded, you have the
older crystals in it and I highly recommend that they be changed with
the matched set of 7 crystals available from Elecraft.  That will change
the attenuation.

Of course, if your filters are not aligned to properly center on your
sidetone pitch, that alone could be the reason for your observations -
that would be more apparent as the width is narrowed (the signal falls
on the slope of the passband rather than at the peak).  See the filter
alignment information on my website www.w3fpr.com - look at part 3  of
the article dealing with K2 Dial Calibration.   Use Spectrogram or
Spectrum Lab or similar to give you a visual picture of the filter
passband placement and the relative amplitude of the filters.

One of the aspects (limitations) of the K2 is that your listening
sidetone pitch cannot be changed at will without peaking the narrow IF
filters at that new sidetone frequency.  You may be able to change the
sidetone pitch by 50 Hz each side of the filter center, but much beyond
that will require that the filter centers be repositioned.

73,
Don W3FPR

On 11/4/2010 2:12 PM, dave wrote:
> I dunno about the loss you are seeing but I've measured about 8 dB of
> loss in my K2 at 200 Hz vs 1 kHz BW. That does strike me a quite a bit
> of loss. I just don't use the narrow filters often. I know of at least
> one other K2 that has similar loss. Anyone else?
>
>
> 73 de dave
> ab9ca/4
>
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[Don Wilhelm-4]

  Petr,

Have you used Spectrogram (or similar) to check the position of the
filter passbands?  If not, you should do so and center the filters at
your chosen sidetone pitch.

73,
Don W3FPR

On 11/4/2010 12:48 PM, ok1rp wrote:
> Hi,
>
> I would like to ask for help. My K2 #4800 works fine but I realized the
> narrower filters have attenuation. I pre-set FL1>200Hz, FL2>400Hz and
> FL3>700Hz but with FL1 I recognised too much attenuation which degrading the
> reception of weaks sigs. Is there something which I am doing wrong please?
>
> 73 - Petr, OK1RP
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[Mike Harris]

G'day,

The filters on K2 #1400 (fully updated):

Mode: CW
AGC: OFF
ATT: ON
Signal source: K3
Frequency: 18120kHz
Pitch Freq: 650Hz

Measured using Spectrogram ref level for audio peak -90dB.  The
sound card in my PC isn't particularly good and this low level
eliminates displayed audio harmonics.

Filter:
1000Hz -90 (ref)
700Hz -90
400Hz -92
200Hz - 94

FWIW.

Regards,

Mike VP8NO


----- Original Message -----
From: "Curt" <[hidden email]>
To: <[hidden email]>
Sent: Thursday, November 04, 2010 10:37 PM
Subject: Re: [Elecraft] [K2] Filters attenuation

> Yes, mine attenuates but haven't bothered to measure it.
> Strangely, the 700
> Hz seems worse than the narrower filters.
>
> Curt KB5JO
>
>>I dunno about the loss you are seeing but I've measured about 8 dB
>>of
>>loss in my K2 at 200 Hz vs 1 kHz BW. That does strike me a quite a
>>bit
>>of loss. I just don't use the narrow filters often. I know of at
>>least
>>one other K2 that has similar loss. Anyone else?

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[Don Wilhelm-4]

  Mike,

Your results are not all that abnormal.  Most do not begin to encounter
attenuation until less than 400 Hz, so yours is slightly worse off than
normal in that regard - but then I usually consider 2 dB to be within
measurement error range.
However, I was concerned about those who said they had significant
attenuation at 700 Hz.

Even though there is attenuation at the narrow filter settings, the
filters are still quite usable for combating QRM.  On the lower bands,
the band-noise is typically high enough that adding more gain is not
beneficial unless your antenna is inefficient, but on the higher bands,
running with the preamp on will more than make up for the few dB loss of
the narrow filter.  In other words, while this is an interesting topic
for those of us with measuring tools (signal generator and Spectrogram),
it is not likely to make a huge difference in actual operating.

73,
Don W3FPR

On 11/5/2010 1:29 PM, Mike Harris wrote:

>
> Measured using Spectrogram ref level for audio peak -90dB.  The
> sound card in my PC isn't particularly good and this low level
> eliminates displayed audio harmonics.
>
> Filter:
> 1000Hz -90 (ref)
> 700Hz -90
> 400Hz -92
> 200Hz - 94
>
> FWIW.
>
> Regards,
>
> Mike VP8NO
>

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[Mike Harris]

Hi Don,

I'm not concerned in the slightest, it is to be expected and was
just another measured data point in the discussion.

Regards,

Mike VP8NO

----- Original Message -----
From: "Don Wilhelm" <[hidden email]>
To: "Mike Harris" <[hidden email]>
Cc: "Curt" <[hidden email]>; <[hidden email]>
Sent: Friday, November 05, 2010 3:12 PM
Subject: Re: [Elecraft] [K2] Filters attenuation

>  Mike,
>
> Your results are not all that abnormal.  Most do not begin to
> encounter
> attenuation until less than 400 Hz, so yours is slightly worse off
> than
> normal in that regard - but then I usually consider 2 dB to be
> within
> measurement error range.
> However, I was concerned about those who said they had significant
> attenuation at 700 Hz.
>
> Even though there is attenuation at the narrow filter settings,
> the
> filters are still quite usable for combating QRM.  On the lower
> bands,
> the band-noise is typically high enough that adding more gain is
> not
> beneficial unless your antenna is inefficient, but on the higher
> bands,
> running with the preamp on will more than make up for the few dB
> loss of
> the narrow filter.  In other words, while this is an interesting
> topic
> for those of us with measuring tools (signal generator and
> Spectrogram),
> it is not likely to make a huge difference in actual operating.
>
> 73,
> Don W3FPR
>
> On 11/5/2010 1:29 PM, Mike Harris wrote:
>>
>> Measured using Spectrogram ref level for audio peak -90dB.  The
>> sound card in my PC isn't particularly good and this low level
>> eliminates displayed audio harmonics.
>>
>> Filter:
>> 1000Hz -90 (ref)
>> 700Hz -90
>> 400Hz -92
>> 200Hz - 94
>>
>> FWIW.
>>
>> Regards,
>>
>> Mike VP8NO
>>

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