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Crystal Filter Offset in 4.81, What does it mean?

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Mike K2MK

Crystal Filter Offset in 4.81, What does it mean?

I installed the 4.81 beta firmware and I am able to change the crystal filter offset as described in the firmware notes. I can hear slight differences in a CW signal between 0.1, 0.2, and 0.3 KHz. What I don't understand is what does it mean. Previous to this release I would have assumed that the crystal filter is centered on my chosen CW pitch suggesting a 0 KHz offset. If I choose one of the 3 offsets am I now listening (and transmitting) slightly off zero beat. Why would I want this? Wouldn't I also want a 4th choice of 0 KHz?

Explanations in layman's terms would be appreciated.

73,
Mike K2MK

alsopb

Re: Crystal Filter Offset in 4.81, What does it mean?

Guys,

I ran a sweep of the filter response with a 400 Hz filter at nominal 0.2
and 03.

I have the plot but can't post here.

In short the left side of the filter response is moved to the right.
The right side moves slightly inward as well.

The net effect is a narrowing of the filter -6db bandwidth and also a
small shift in center frequency.

Here are the numbers:

BW (-6dB) =380 Hz, center 485 Hz @ 0.2
BW (-6db) =300 Hz, center 508 Hz @ 0.3

It appears if you do this, you might also have to adjust the filter
offset to bring the center of the passband back to the nominal pitch value.

73 de Brian/K3KO

On 2/5/2014 13:40, Mike K2MK wrote:

> I installed the 4.81 beta firmware and I am able to change the crystal filter
> offset as described in the firmware notes. I can hear slight differences in
> a CW signal between 0.1, 0.2, and 0.3 KHz. What I don't understand is what
> does it mean. Previous to this release I would have assumed that the crystal
> filter is centered on my chosen CW pitch suggesting a 0 KHz offset. If I
> choose one of the 3 offsets am I now listening (and transmitting) slightly
> off zero beat. Why would I want this? Wouldn't I also want a 4th choice of 0
> KHz?
>
> Explanations in layman's terms would be appreciated.
>
> 73,
> Mike K2MK
>
>
>
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/Crystal-Filter-Offset-in-4-81-What-does-it-mean-tp7583674.html
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alsopb

Re: Crystal Filter Offset in 4.81, What does it mean?

I should also point out that his shows no measurable effect on the 250
and 200 Hz filters. 400Hz and wider are impacted.

On 2/5/2014 14:37, Brian Alsop wrote:

> Guys,
>
> I ran a sweep of the filter response with a 400 Hz filter at nominal 0.2
> and 03.
>
> I have the plot but can't post here.
>
> In short the left side of the filter response is moved to the right. The
> right side moves slightly inward as well.
>
> The net effect is a narrowing of the filter -6db bandwidth and also a
> small shift in center frequency.
>
> Here are the numbers:
>
> BW (-6dB) =380 Hz, center 485 Hz @ 0.2
> BW (-6db) =300 Hz, center 508 Hz @ 0.3
>
> It appears if you do this, you might also have to adjust the filter
> offset to bring the center of the passband back to the nominal pitch value.
>
> 73 de Brian/K3KO
>
> On 2/5/2014 13:40, Mike K2MK wrote:
>> I installed the 4.81 beta firmware and I am able to change the crystal
>> filter
>> offset as described in the firmware notes. I can hear slight
>> differences in
>> a CW signal between 0.1, 0.2, and 0.3 KHz. What I don't understand is
>> what
>> does it mean. Previous to this release I would have assumed that the
>> crystal
>> filter is centered on my chosen CW pitch suggesting a 0 KHz offset. If I
>> choose one of the 3 offsets am I now listening (and transmitting)
>> slightly
>> off zero beat. Why would I want this? Wouldn't I also want a 4th
>> choice of 0
>> KHz?
>>
>> Explanations in layman's terms would be appreciated.
>>
>> 73,
>> Mike K2MK
>>
>>
>>
>> --
>> View this message in context:
>> http://elecraft.365791.n2.nabble.com/Crystal-Filter-Offset-in-4-81-What-does-it-mean-tp7583674.html
>>
>> Sent from the Elecraft mailing list archive at Nabble.com.
>> ______________________________________________________________
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>> Checked by AVG - www.avg.com
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>>
>>
>
>
>
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Joe Subich, W4TV-4

Re: Crystal Filter Offset in 4.81, What does it mean?

On 2/5/2014 9:55 AM, Brian Alsop wrote:
> I should also point out that his shows no measurable effect on the
> 250 and 200 Hz filters.

It will if you choose a 300 Hz offset and Pitch less than 425 Hz for
the 250 Hz filter or a 300 Hz offset and pitch less than 400 Hz for
the 200 Hz filter.

One will see effects due to staggering the IF and DSP filters if the
selected Pitch is less than [Offset + (IF Filter width)/2].

73,

... Joe, W4TV

On 2/5/2014 9:55 AM, Brian Alsop wrote:

> I should also point out that his shows no measurable effect on the 250
> and 200 Hz filters. 400Hz and wider are impacted.
>
> On 2/5/2014 14:37, Brian Alsop wrote:
>> Guys,
>>
>> I ran a sweep of the filter response with a 400 Hz filter at nominal 0.2
>> and 03.
>>
>> I have the plot but can't post here.
>>
>> In short the left side of the filter response is moved to the right. The
>> right side moves slightly inward as well.
>>
>> The net effect is a narrowing of the filter -6db bandwidth and also a
>> small shift in center frequency.
>>
>> Here are the numbers:
>>
>> BW (-6dB) =380 Hz, center 485 Hz @ 0.2
>> BW (-6db) =300 Hz, center 508 Hz @ 0.3
>>
>> It appears if you do this, you might also have to adjust the filter
>> offset to bring the center of the passband back to the nominal pitch
>> value.
>>
>> 73 de Brian/K3KO
>>
>> On 2/5/2014 13:40, Mike K2MK wrote:
>>> I installed the 4.81 beta firmware and I am able to change the crystal
>>> filter
>>> offset as described in the firmware notes. I can hear slight
>>> differences in
>>> a CW signal between 0.1, 0.2, and 0.3 KHz. What I don't understand is
>>> what
>>> does it mean. Previous to this release I would have assumed that the
>>> crystal
>>> filter is centered on my chosen CW pitch suggesting a 0 KHz offset. If I
>>> choose one of the 3 offsets am I now listening (and transmitting)
>>> slightly
>>> off zero beat. Why would I want this? Wouldn't I also want a 4th
>>> choice of 0
>>> KHz?
>>>
>>> Explanations in layman's terms would be appreciated.
>>>
>>> 73,
>>> Mike K2MK
>>>
>>>
>>>
>>> --
>>> View this message in context:
>>> http://elecraft.365791.n2.nabble.com/Crystal-Filter-Offset-in-4-81-What-does-it-mean-tp7583674.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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>>>
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>>> Checked by AVG - www.avg.com
>>> Version: 2012.0.2247 / Virus Database: 3684/6563 - Release Date:
>>> 02/05/14
>>>
>>>
>>
>>
>>
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>> Checked by AVG - www.avg.com
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>
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Lyle Johnson

Re: Crystal Filter Offset in 4.81, What does it mean?

In reply to this post by alsopb

The "center of the passband to the nominal pitch value" only occurs at
higher pitches and/or narrower passbands.

Think about the case where you have 1.5 kHz width selected and a pitch
of 500 Hz. You defintely do NOT want the center of the filter and the
pitch to be equal,or you'd have terrible opposite sideband suppression.

The calculations done internally in the K3 to adjust the IF and AF
passbands based on the settings of center frequency, width and pitch are
fairly complex.

"Zero beat" has to do with frequencies, not filter responses, and
changing the filter edge should have no practical effect on whether or
not you are zero beat. I say practical because the calculations done
inside the radio coupled with finite resolution of the various
oscillators may result in a 1 or 2 Hz difference, and someone is bound
to measure this :-)

Finally, the new offsets apply to receive only. They have zero effect on
how the radio is configured on transmit.

73,

Lyle KK7P

> ...
>
> It appears if you do this, you might also have to adjust the filter
> offset to bring the center of the passband back to the nominal pitch
> value.
> ...
>> I installed the 4.81 beta firmware and I am able to change the
>> crystal filter
>> offset as described in the firmware notes... Previous to this release
>> I would have assumed that the crystal
>> filter is centered on my chosen CW pitch suggesting a 0 KHz offset. If I
>> choose one of the 3 offsets am I now listening (and transmitting)
>> slightly
>> off zero beat...

wayne burdick

Re: Crystal Filter Offset in 4.81, What does it mean?

Administrator

In reply to this post by Mike K2MK

This just establishes the low-pitched rolloff by adjusting the filter position relative to zero-beat.

Setting it to 0.1 or 0.2 (the default) will have the least impact on the CW passband. 0.1 provides better low-end audio. 0.3 is for cases where you have such extreme signals that you need to lop off a bit more of the low end to eliminate any vestige of low-pitched opposite-sideband signals. For 99% of users, 0.1 or 0.2 will suffice.

Shifting the crystal filter center frequencies should not be necessary. I recommend just sticking with the offsets printed on the filters (0.00 for all 8-pole filters).

73,
Wayne
N6KR

On Feb 5, 2014, at 5:40 AM, Mike K2MK <[hidden email]> wrote:

Wes (N7WS)

Re: Crystal Filter Offset in 4.81, What does it mean?

In reply to this post by Lyle Johnson

Already noted. See the footnote here:
http://elecraft.365791.n2.nabble.com/Ref-Osc-Cal-Method-4-tc2595451.html

On 2/5/2014 8:35 AM, Lyle Johnson wrote:

>
> "Zero beat" has to do with frequencies, not filter responses, and changing the
> filter edge should have no practical effect on whether or not you are zero
> beat. I say practical because the calculations done inside the radio coupled
> with finite resolution of the various oscillators may result in a 1 or 2 Hz
> difference, and _someone is bound to measure this :-) _
>
>
> 73,
>
> Lyle KK7P

Doug Alspaugh

Re: Crystal Filter Offset in 4.81, What does it mean?

It does effect what CW skimmer sees. At least it does here. I have to set .1 to get skimmer to decode.

73 Doug N3QW

"Wes (N7WS)" <[hidden email]> wrote:

>Already noted. See the footnote here:
>http://elecraft.365791.n2.nabble.com/Ref-Osc-Cal-Method-4-tc2595451.html
>
>On 2/5/2014 8:35 AM, Lyle Johnson wrote:
>>
>> "Zero beat" has to do with frequencies, not filter responses, and
>changing the
>> filter edge should have no practical effect on whether or not you are
>zero
>> beat. I say practical because the calculations done inside the radio
>coupled
>> with finite resolution of the various oscillators may result in a 1
>or 2 Hz
>> difference, and _someone is bound to measure this :-) _
>>
>>
>> 73,
>>
>> Lyle KK7P
>
>______________________________________________________________
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--
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wayne burdick

Re: Crystal Filter Offset in 4.81, What does it mean?

Administrator

I don't understand how this could affect Skimmer. This is a shift pertaining to the CW passband that the operator hears.

Wayne
N6KR

On Feb 5, 2014, at 4:17 PM, Doug Alspaugh <[hidden email]> wrote:

> It does effect what CW skimmer sees. At least it does here. I have to set .1 to get skimmer to decode.
>
> 73 Doug N3QW
>
> "Wes (N7WS)" <[hidden email]> wrote:
>
>> Already noted. See the footnote here:
>> http://elecraft.365791.n2.nabble.com/Ref-Osc-Cal-Method-4-tc2595451.html
>>
>> On 2/5/2014 8:35 AM, Lyle Johnson wrote:
>>>
>>> "Zero beat" has to do with frequencies, not filter responses, and
>> changing the
>>> filter edge should have no practical effect on whether or not you are
>> zero
>>> beat. I say practical because the calculations done inside the radio
>> coupled
>>> with finite resolution of the various oscillators may result in a 1
>> or 2 Hz
>>> difference, and _someone is bound to measure this :-) _
>>>
>>>
>>> 73,
>>>
>>> Lyle KK7P
>>
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>
> --
> Sent from my Android phone with K-9 Mail. Please excuse my brevity.
> ______________________________________________________________
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Arie Kleingeld PA3A-2

Re: Crystal Filter Offset in 4.81, What does it mean?

In reply to this post by Lyle Johnson

Lyle,

What are you saying here?
The DSP filtering as a second IF would do (and I quote you) a /terrible/
job. :-)

73,
Arie PA3A

Lyle Johnson schreef op 5-2-2014 16:35:
<snip>
> The "center of the passband to the nominal pitch value" only occurs at
> higher pitches and/or narrower passbands.
>
> Think about the case where you have 1.5 kHz width selected and a pitch
> of 500 Hz. You defintely do NOT want the center of the filter and the
> pitch to be equal,or you'd have /_terrible _/opposite sideband
> suppression.
>
>
<snip>
> 73,
>
> Lyle KK7P

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DL6OAP

Re: Crystal Filter Offset in 4.81, What does it mean?

In my MarkV Field, I can switch the (2.4k?) SSB filter into the path while receiving in CW mode (500 Hz pitch) and don't "see" the other sideband at all due to the DSP which adds the sideband suppression almost for free (I can turn the DSP off and then I hear the other sideband). The same should apply to the K3, shouldn't it?!?

Greetings

Ralf, DL6OAP

Am 06.02.2014 um 16:14 schrieb Arie Kleingeld PA3A <[hidden email]>:

> Lyle,
>
> What are you saying here?
> The DSP filtering as a second IF would do (and I quote you) a /terrible/ job. :-)
>
> 73,
> Arie PA3A
>
>
> Lyle Johnson schreef op 5-2-2014 16:35:
> <snip>
>> The "center of the passband to the nominal pitch value" only occurs at higher pitches and/or narrower passbands.
>>
>> Think about the case where you have 1.5 kHz width selected and a pitch of 500 Hz. You defintely do NOT want the center of the filter and the pitch to be equal,or you'd have /_terrible _/opposite sideband suppression.
>>
>>
> <snip>
>> 73,
>>
>> Lyle KK7P
>
> ______________________________________________________________
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Don Wilhelm-4

Re: Crystal Filter Offset in 4.81, What does it mean?

In reply to this post by Arie Kleingeld PA3A-2

Arnie,

Think about it this way -- take a filter width of 1500 Hz and a sidetone
pitch of 600 Hz.
If you center the passband at 600 Hz, the upper passband limit will be
at 1350 Hz, but the lower edge will be 150 Hz into the opposite sideband
(single signal reception goes "bye-bye").

The proper position if the passband is to place the lower edge at about
100 Hz, and the upper edge will extend to 1600 Hz.

That is true for any passband that is greater than 2 times the passband
width.

73,
Don W3FPR

On 2/6/2014 10:14 AM, Arie Kleingeld PA3A wrote:

> Lyle,
>
> What are you saying here?
> The DSP filtering as a second IF would do (and I quote you) a
> /terrible/ job. :-)
>
> 73,
> Arie PA3A
>
>
> Lyle Johnson schreef op 5-2-2014 16:35:
> <snip>
>> The "center of the passband to the nominal pitch value" only occurs
>> at higher pitches and/or narrower passbands.
>>
>> Think about the case where you have 1.5 kHz width selected and a
>> pitch of 500 Hz. You defintely do NOT want the center of the filter
>> and the pitch to be equal,or you'd have /_terrible _/opposite
>> sideband suppression.
>>

Arie Kleingeld PA3A-2

Re: Crystal Filter Offset in 4.81, What does it mean?

Don,

I understand this.

Let me explain my thoughts.
Let's suppose we have the different IF's. One analog, the 8Mhz stuff,
and then a "DSP IF" which is fed by the second 15kHz IF.

I am not a DSP expert. But I would expect that the DSP filter would
filter out whatever bandwidth I would want it to, just like it were
analog and better. I expect this function of any IF filter, digital and
analog.
What we are tallking about is that the opposite sideband can pass
through the analog part of the K3 (because of the wide roofing filter)
and yes it does if the skirt of the filter allows it. If this is not
solved in the DSP, the /function/ of the DSP is not more than the old
type audio DSP filter we had in the old days (apart from partly being
inside the AGC-loop)

As Ralph DL5OAP already stated: Even the old FT1000MP with DSP
demodulation killed the opposite sideband. I had an MP for a long time
(before I got the K3) and I can confirm this. I had it switched on all
the time.

As you said Don, the K3 really needs the analog roofing filter to be in
place to reach its best performance. Good thing that I have them for the
bandwidths I use. And overall it works pretty well. There are still some
things to improve though.

73
Arie
(not Arnie :-))

Don Wilhelm schreef op 6-2-2014 17:21:

Don Wilhelm-4

Re: Crystal Filter Offset in 4.81, What does it mean?

In reply to this post by Don Wilhelm-4

Sorry, Change the last "passband width" to "sidetone pitch"
My thoughts an fingers got mixed up, and I am old enough to claim a
"senior moment":-)

73,
Don W3FPR

On 2/6/2014 11:21 AM, Don Wilhelm wrote:

> Arnie,
>
> Think about it this way -- take a filter width of 1500 Hz and a
> sidetone pitch of 600 Hz.
> If you center the passband at 600 Hz, the upper passband limit will be
> at 1350 Hz, but the lower edge will be 150 Hz into the opposite
> sideband (single signal reception goes "bye-bye").
>
> The proper position if the passband is to place the lower edge at
> about 100 Hz, and the upper edge will extend to 1600 Hz.
>
> That is true for any passband that is greater than 2 times the
> passband width.
>
> 73,
> Don W3FPR
>
> On 2/6/2014 10:14 AM, Arie Kleingeld PA3A wrote:
>> Lyle,
>>
>> What are you saying here?
>> The DSP filtering as a second IF would do (and I quote you) a
>> /terrible/ job. :-)
>>
>> 73,
>> Arie PA3A
>>
>>
>> Lyle Johnson schreef op 5-2-2014 16:35:
>> <snip>
>>> The "center of the passband to the nominal pitch value" only occurs
>>> at higher pitches and/or narrower passbands.
>>>
>>> Think about the case where you have 1.5 kHz width selected and a
>>> pitch of 500 Hz. You defintely do NOT want the center of the filter
>>> and the pitch to be equal,or you'd have /_terrible _/opposite
>>> sideband suppression.
>>>
>
> ______________________________________________________________
> Elecraft mailing list
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wayne burdick

Re: Crystal Filter Offset in 4.81, What does it mean?

Administrator

In reply to this post by Arie Kleingeld PA3A-2

Arie Kleingeld PA3A <[hidden email]> wrote:

> Lyle,
>
> What are you saying here?

Arie,

The K3 has excellent opposite sideband suppression (the combined suppression of the crystal filters in the first I.F., and the DSP in the second I.F.).

The present change (allowing you to move the crystal filter edge) came about because exactly *one* customer in England claimed to be hearing an OSB image at extremely low pitch in CW mode in the presence of "monster" signals. This was the first such comment I had heard about the K3, which isn't bad considering we've shipped some 8000 of them.

We added the new menu entry to satisfy this demanding customer because, as I told him a the time, I didn't want anyone to ever hear an OSB image, no matter how small, on the K3. He's using the 0.3-kHz setting, though I couldn't tell any difference between 0.2 (the default) and 0.3.

At one point in the K3's history, 0.1 was the setting used. Even then there were no complaints about OSB images, so if you want lower pitch, go for it.

73,
Wayne
N6KR

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Don Wilhelm-4

Re: Crystal Filter Offset in 4.81, What does it mean?

In reply to this post by Arie Kleingeld PA3A-2

Arie,

Sorry about the added "n".

Yes, the DSP algorithms will not allow the passband to extend into the
opposite sideband.
What I was responding to was the initial statement about "centering" the
passband (on the CW sidetone pitch), and I was pointing out the fallacy
of that when the filter is wide.

The analog filters at the 8 MHz have only the task of keeping strong
nearby signals out of the ADC and not overloading it - they also reduce
the exposure of 'pumping' for the hardware AGC by those strong signals
near in frequency (such as may be encountered in a DX pileup or contest
conditions).
The DSP does the final filtering, and the DSP filters do not actually
need the roofing filters at all other than for the reasons stated above.

73,
Don W3FPR

On 2/6/2014 12:17 PM, Arie Kleingeld PA3A wrote:

> Don,
>
> I understand this.
>
> Let me explain my thoughts.
> Let's suppose we have the different IF's. One analog, the 8Mhz stuff,
> and then a "DSP IF" which is fed by the second 15kHz IF.
>
> I am not a DSP expert. But I would expect that the DSP filter would
> filter out whatever bandwidth I would want it to, just like it were
> analog and better. I expect this function of any IF filter, digital
> and analog.
> What we are tallking about is that the opposite sideband can pass
> through the analog part of the K3 (because of the wide roofing filter)
> and yes it does if the skirt of the filter allows it. If this is not
> solved in the DSP, the /function/ of the DSP is not more than the old
> type audio DSP filter we had in the old days (apart from partly being
> inside the AGC-loop)
>
> As Ralph DL5OAP already stated: Even the old FT1000MP with DSP
> demodulation killed the opposite sideband. I had an MP for a long time
> (before I got the K3) and I can confirm this. I had it switched on all
> the time.
>
> As you said Don, the K3 really needs the analog roofing filter to be
> in place to reach its best performance. Good thing that I have them
> for the bandwidths I use. And overall it works pretty well. There are
> still some things to improve though.
>
> 73
> Arie
> (not Arnie :-))
>
>
> Don Wilhelm schreef op 6-2-2014 17:21:
>> Arnie,
>>
>> Think about it this way -- take a filter width of 1500 Hz and a
>> sidetone pitch of 600 Hz.
>> If you center the passband at 600 Hz, the upper passband limit will
>> be at 1350 Hz, but the lower edge will be 150 Hz into the opposite
>> sideband (single signal reception goes "bye-bye").
>>
>> The proper position if the passband is to place the lower edge at
>> about 100 Hz, and the upper edge will extend to 1600 Hz.
>>

Wes (N7WS)

Re: Crystal Filter Offset in 4.81, What does it mean?

Actually, the crystal filters have two purposes:

1) Eliminate the 15 KHz image that would otherwise be a problem

2) As Don said; however, it's the 2nd mixer that needs more protection than the DSP.

Wes N7WS

On 2/6/2014 11:38 AM, Don Wilhelm wrote:

> Arie,
>
> Sorry about the added "n".
>
> Yes, the DSP algorithms will not allow the passband to extend into the
> opposite sideband.
> What I was responding to was the initial statement about "centering" the
> passband (on the CW sidetone pitch), and I was pointing out the fallacy of
> that when the filter is wide.
>
> The analog filters at the 8 MHz have only the task of keeping strong nearby
> signals out of the ADC and not overloading it - they also reduce the exposure
> of 'pumping' for the hardware AGC by those strong signals near in frequency
> (such as may be encountered in a DX pileup or contest conditions).
> The DSP does the final filtering, and the DSP filters do not actually need the
> roofing filters at all other than for the reasons stated above.
>
> 73,
> Don W3FPR
>