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K3 Receiver Noise Level -- Evaluation and Adjustment

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wayne burdick

K3 Receiver Noise Level -- Evaluation and Adjustment

Administrator

The K3 has a lot of overall gain. This is necessary to provide
sufficient speaker output in operating locations with high ambient
noise levels.

But you can adjust the amount of gain, and shape it, to meet your needs.

If you feel that the noise level of your K3's receiver is excessive,
please try the following:

1. Turn off the preamp. In many cases it is not needed (especially
below 20 m), because the receiver is still very sensitive working
directly into the mixer.

2. If overall AF gain is higher than needed for your headphones or
speaker, set CONFIG:AF GAIN to LOW. This makes the K3's audio output
level (and overall gain) very similar to a K2.

3. Use the factory defaults for AGC. These were carefully chosen to
adjust gain in the presence of significant band noise.

4. Use narrow filter bandwidths when listening to narrow-band modes
(CW or DATA). Noise output is proportional to bandwidth, and in narrow-
band modes, reducing WIDTH can dramatically reduce the signal-to-noise
ratio. I strongly recommend installing at least one narrow crystal
filter (500 Hz or lower) if you use CW or DATA modes. The K3's entire
receiver philosophy is built around the use of roofing filters that
are matched to the operating mode.

5. Use noise reduction. NR is specifically designed to reduce wideband
stochastic (white) noise. I suggest using the lowest setting (F1-1) to
obtain a modest noise-reduction benefit with minimum impact on signal
characteristics.

6. If you're sensitive to high-pitched noise, consider installing (or
having us install) the new DSP low-pass filter (LPF) module. (Contact
k3support for details.) This filter rolls off everything at about 4.5
kHz, including some low-level AF sampling artifacts from 10-14 kHz
that some operators with excellent ears can hear. The LPF module,
which is easy to install, can improve the overall listening
experience. It has already been phased into production.

7. If you still feel that noise level is too high, try doing an MDS
(minimum-discernable signal) test to see if the receiver is meeting
spec. You can use your own signal generator or an Elecraft XG1 or XG2,
in conjunction with the K3's built-in true-RMS AF voltmeter (see
alternate VFO B display modes in the owner's manual).

73,
Wayne
N6KR

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Mike Reublin

Re: K3 Receiver Noise Level -- Evaluation and Adjustment

Wayne -

Could you explain the MDS test in greater detail? My AFV (AGC-S, ATT
off, no sub reciever) value bounces all over between 18 and 62, with
most values in the mid 20's. Over a 5 minute period, it doesn't
stabilize. I don't know what that means.

73, Mike NF4L

Wayne Burdick wrote:
> 7. If you still feel that noise level is too high, try doing an MDS
> (minimum-discernable signal) test to see if the receiver is meeting
> spec. You can use your own signal generator or an Elecraft XG1 or XG2,
> in conjunction with the K3's built-in true-RMS AF voltmeter (see
> alternate VFO B display modes in the owner's manual).
>
> 73,
> Wayne
> N6KR

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Buck - k4ia

Re: K3 Receiver Noise Level -- Evaluation and Adjustment

In reply to this post by wayne burdick

Wayne

Is the low pass filter module available separate from the entire DSP Rev C
board replacement? If so, what does it cost and how complicated is it to
install?

Buck
k4ia
K3 #101

In a message dated 12/18/2009 10:12:29 A.M. Eastern Standard Time,
[hidden email] writes:

The K3 has a lot of overall gain. This is necessary to provide
sufficient speaker output in operating locations with high ambient
noise levels.

But you can adjust the amount of gain, and shape it, to meet your needs.

If you feel that the noise level of your K3's receiver is excessive,
please try the following:

1. Turn off the preamp. In many cases it is not needed (especially
below 20 m), because the receiver is still very sensitive working
directly into the mixer.

2. If overall AF gain is higher than needed for your headphones or
speaker, set CONFIG:AF GAIN to LOW. This makes the K3's audio output
level (and overall gain) very similar to a K2.

3. Use the factory defaults for AGC. These were carefully chosen to
adjust gain in the presence of significant band noise.

4. Use narrow filter bandwidths when listening to narrow-band modes
(CW or DATA). Noise output is proportional to bandwidth, and in narrow-
band modes, reducing WIDTH can dramatically reduce the signal-to-noise
ratio. I strongly recommend installing at least one narrow crystal
filter (500 Hz or lower) if you use CW or DATA modes. The K3's entire
receiver philosophy is built around the use of roofing filters that
are matched to the operating mode.

5. Use noise reduction. NR is specifically designed to reduce wideband
stochastic (white) noise. I suggest using the lowest setting (F1-1) to
obtain a modest noise-reduction benefit with minimum impact on signal
characteristics.

6. If you're sensitive to high-pitched noise, consider installing (or
having us install) the new DSP low-pass filter (LPF) module. (Contact
k3support for details.) This filter rolls off everything at about 4.5
kHz, including some low-level AF sampling artifacts from 10-14 kHz
that some operators with excellent ears can hear. The LPF module,
which is easy to install, can improve the overall listening
experience. It has already been phased into production.

7. If you still feel that noise level is too high, try doing an MDS
(minimum-discernable signal) test to see if the receiver is meeting
spec. You can use your own signal generator or an Elecraft XG1 or XG2,
in conjunction with the K3's built-in true-RMS AF voltmeter (see
alternate VFO B display modes in the owner's manual).

73,
Wayne
N6KR

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Joe Subich, W4TV-4

Re: K3 Receiver Noise Level -- Evaluation and Adjustment

I had this same exchange with Eric earlier today ...

1) the LPF board will be available "shortly." It is in stock
and will added (along with instructions) to the web page
soon (I read that as the next day or two).

2) The DSP upgrade now being shipped is "Rev D" which is "Rev C"
(the low frequency enhancement) plus the LPF board (the ADC
spurious elimination filter).

I did not get price information on the LPF board but was assured
it will be up with the rest of the information.

73,

... Joe, W4TV

> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]] On Behalf Of [hidden email]
> Sent: Friday, December 18, 2009 5:11 PM
> To: [hidden email]; [hidden email]
> Subject: Re: [Elecraft] K3 Receiver Noise Level -- Evaluation
> and Adjustment
>
>
> Wayne
>
> Is the low pass filter module available separate from the
> entire DSP Rev C
> board replacement? If so, what does it cost and how
> complicated is it to
> install?
>
> Buck
> k4ia
> K3 #101
>
>
> In a message dated 12/18/2009 10:12:29 A.M. Eastern Standard Time,
> [hidden email] writes:
>
> The K3 has a lot of overall gain. This is necessary to provide
> sufficient speaker output in operating locations with high ambient
> noise levels.
>
> But you can adjust the amount of gain, and shape it, to meet
> your needs.
>
> If you feel that the noise level of your K3's receiver is
> excessive,
> please try the following:
>
> 1. Turn off the preamp. In many cases it is not needed (especially
> below 20 m), because the receiver is still very sensitive working
> directly into the mixer.
>
> 2. If overall AF gain is higher than needed for your headphones or
> speaker, set CONFIG:AF GAIN to LOW. This makes the K3's audio
> output
> level (and overall gain) very similar to a K2.
>
> 3. Use the factory defaults for AGC. These were carefully chosen to
> adjust gain in the presence of significant band noise.
>
> 4. Use narrow filter bandwidths when listening to narrow-band modes
> (CW or DATA). Noise output is proportional to bandwidth, and
> in narrow-
> band modes, reducing WIDTH can dramatically reduce the
> signal-to-noise
> ratio. I strongly recommend installing at least one narrow crystal
> filter (500 Hz or lower) if you use CW or DATA modes. The
> K3's entire
> receiver philosophy is built around the use of roofing filters that
> are matched to the operating mode.
>
> 5. Use noise reduction. NR is specifically designed to
> reduce wideband
> stochastic (white) noise. I suggest using the lowest setting
> (F1-1) to
> obtain a modest noise-reduction benefit with minimum impact
> on signal
> characteristics.
>
> 6. If you're sensitive to high-pitched noise, consider
> installing (or
> having us install) the new DSP low-pass filter (LPF) module.
> (Contact
> k3support for details.) This filter rolls off everything at
> about 4.5
> kHz, including some low-level AF sampling artifacts from 10-14 kHz
> that some operators with excellent ears can hear. The LPF module,
> which is easy to install, can improve the overall listening
> experience. It has already been phased into production.
>
> 7. If you still feel that noise level is too high, try doing an MDS
> (minimum-discernable signal) test to see if the receiver is meeting
> spec. You can use your own signal generator or an Elecraft
> XG1 or XG2,
> in conjunction with the K3's built-in true-RMS AF voltmeter (see
> alternate VFO B display modes in the owner's manual).
>
> 73,
> Wayne
> N6KR
>

Mike Harris

Re: K3 Receiver Noise Level -- Evaluation and Adjustment

Splendid news, why obtaining it had to be like pulling teeth I
cannot fathom. The noisy RX thread would have dried up before it
reached the present head of steam.

Regards,

Mike VP8NO

----- Original Message -----
From: "Joe Subich, W4TV" <[hidden email]>
To: <[hidden email]>; <[hidden email]>
Sent: Friday, December 18, 2009 8:12 PM
Subject: Re: [Elecraft] K3 Receiver Noise Level -- Evaluation and
Adjustment

>
> I had this same exchange with Eric earlier today ...
>
> 1) the LPF board will be available "shortly." It is in stock
> and will added (along with instructions) to the web page
> soon (I read that as the next day or two).
>
> 2) The DSP upgrade now being shipped is "Rev D" which is "Rev C"
> (the low frequency enhancement) plus the LPF board (the ADC
> spurious elimination filter).
>
> I did not get price information on the LPF board but was assured
> it will be up with the rest of the information.
>
> 73,
>
> ... Joe, W4TV

Bill K9YEQ

Re: K3 Receiver Noise Level -- Evaluation and Adjustment

I think the staff at Elecraft is overwhelmed with orders and business as
usual. I can understand the workload during this time of year, and I am
sure the engineering process skills will improve next year. I would bet
their growth is somewhat beyond what they had anticipated.

73,

Bill
K9YEQ
K2 #35; KX1 #35; K3 #1744; mini mods
ATS-3B

-----Original Message-----

Splendid news, why obtaining it had to be like pulling teeth I
cannot fathom. The noisy RX thread would have dried up before it
reached the present head of steam.

Regards,

Mike VP8NO

----- Original Message -----

Bill K9YEQ

Re: K3 Receiver Noise Level -- Evaluation and Adjustment

In reply to this post by Mike Harris

I just reread my message and I don't like the meaning of the content. I
meant to say that Elecraft is having such a successful year that they may be
a bit overwhelmed. The offerings of excellent equipment and attention to
detail is excellent. I don't know how they can keep up. But keep it
coming. I am an early customer of theirs and can't tell you enough how much
I appreciate my enjoyment of the hobby since I came on board, back in '99
was it?? The entire staff is very dedicated. I am sure they will come up
with new ways to meet our increasing demands. They always have. So will
keep on putting the feedback on the reflector to help them adjust. I love
the Elecraft brand.

Bill
K9YEQ
......................................................................
I think the staff at Elecraft is overwhelmed with orders and business as
usual. I can understand the workload during this time of year, and I am
sure the engineering process skills will improve next year. I would bet
their growth is somewhat beyond what they had anticipated.

73,

Bill
K9YEQ
K2 #35; KX1 #35; K3 #1744; mini mods
ATS-3B

-----Original Message-----

Splendid news, why obtaining it had to be like pulling teeth I
cannot fathom. The noisy RX thread would have dried up before it
reached the present head of steam.

Regards,

Mike VP8NO

----- Original Message -----

______________________________________________________________
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______________________________________________________________
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Bill K9YEQ

Re: K3 Receiver Noise Level -- Evaluation and Adjustment

In reply to this post by Mike Harris

I just reread my message and I don't like the meaning of the content. I
meant to say that Elecraft is having such a successful year that they may be
a bit overwhelmed. The offerings of excellent equipment and attention to
detail is excellent. I don't know how they can keep up. But keep it
coming. I am an early customer of their's and can't tell you how much I
appreciate my enjoyment of the hobby since I came on board back in '99I
think the staff at Elecraft is overwhelmed with orders and business as
usual. I can understand the workload during this time of year, and I am
sure the engineering process skills will improve next year. I would bet
their growth is somewhat beyond what they had anticipated.

73,

Bill
K9YEQ
K2 #35; KX1 #35; K3 #1744; mini mods
ATS-3B

-----Original Message-----

Splendid news, why obtaining it had to be like pulling teeth I
cannot fathom. The noisy RX thread would have dried up before it
reached the present head of steam.

Regards,

Mike VP8NO

----- Original Message -----

Guy, K2AV

Re: K3 Receiver Noise Level -- Evaluation and Adjustment

In reply to this post by wayne burdick

Short version: put a way to reset to default AGC in the K3 itself. Do this ASAP.

Long version:

On Fri, Dec 18, 2009 at 10:11 AM, Wayne Burdick <[hidden email]> wrote:

> If you feel that the noise level of your K3's receiver is excessive,
> please try the following:

....snip....

> 3. Use the factory defaults for AGC. These were carefully chosen to
> adjust gain in the presence of significant band noise.

....snip....

While the advice is official, there is not much point in posting "set
to factory defaults" unless you include what those numbers are in your
text.

Otherwise the reader has to do the research (Google, site search,
thumb manual looking for numbers...) to determine what the factory
defaults are.

Digging around on the web site, etc, will defeat a lot of readers. Not
because your site is trashy (it's not), or the manual is bad (it's
not), or K3 users are stupid (they're not), but because in human
evolution web-searching was never the reason why one did or didn't
live long enough to pass on one's genes to one's children. That and
such things as RTFM were not Darwinian criteria. More than that...

Human behavior studies in information assimilation on all kinds of us
regular folks show over and over that on average humans don't do well
at drilling down in information, become quickly bored, tired,
irritated, frustrated, confused just to name a few. And while they may
doggedly stay with such tasks to keep a job to feed and house the
family, teeth-grinding information drilling to find the default
numbers does not cut it in our pastime activities. Moreover, even
relating to work, studies with competent well-thought-of clerical
personnel showed that errors, misreads, no-finds, and nasty remarks
increased dramatically with the number of steps to fetch, or with any
uncertainty as to the source, appearance or presentation of the needed
information.

Given the amount of attention, confusion and complaints related to
noise and AGC, wouldn't it make sense to identify your default
CONFIG:AGCxxx setting numbers with a "dEF" to the left of the number
when VFO A rolls over it, so that when the folks from Mount Aptos say
to use the default AGC, that can be easily set and/or confirmed and/or
returned to without needing to dig up the numbers somewhere?

73, Guy.
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Ken Wagner K3IU

Re: K3 Receiver Noise Level -- Evaluation and Adjustment

All one has to do is go to the CONFIG menus, select the parameter, and
tap Display and be told what the Default value is for that parameter.
It's easy. It takes less than a minute to do all of the AGC parameters.
That's pretty short.
73, Ken K3IU

On 12/19/2009 12:02 PM, Guy Olinger K2AV wrote:

> Short version: put a way to reset to default AGC in the K3 itself. Do this ASAP.
>
> Long version:
>
> On Fri, Dec 18, 2009 at 10:11 AM, Wayne Burdick<[hidden email]> wrote:
>
>
>> If you feel that the noise level of your K3's receiver is excessive,
>> please try the following:
>>
> ....snip....
>
>
>> 3. Use the factory defaults for AGC. These were carefully chosen to
>> adjust gain in the presence of significant band noise.
>>
> ....snip....
>
> While the advice is official, there is not much point in posting "set
> to factory defaults" unless you include what those numbers are in your
> text.
>
> Otherwise the reader has to do the research (Google, site search,
> thumb manual looking for numbers...) to determine what the factory
> defaults are.
>
> Digging around on the web site, etc, will defeat a lot of readers. Not
> because your site is trashy (it's not), or the manual is bad (it's
> not), or K3 users are stupid (they're not), but because in human
> evolution web-searching was never the reason why one did or didn't
> live long enough to pass on one's genes to one's children. That and
> such things as RTFM were not Darwinian criteria. More than that...
>
> Human behavior studies in information assimilation on all kinds of us
> regular folks show over and over that on average humans don't do well
> at drilling down in information, become quickly bored, tired,
> irritated, frustrated, confused just to name a few. And while they may
> doggedly stay with such tasks to keep a job to feed and house the
> family, teeth-grinding information drilling to find the default
> numbers does not cut it in our pastime activities. Moreover, even
> relating to work, studies with competent well-thought-of clerical
> personnel showed that errors, misreads, no-finds, and nasty remarks
> increased dramatically with the number of steps to fetch, or with any
> uncertainty as to the source, appearance or presentation of the needed
> information.
>
> Given the amount of attention, confusion and complaints related to
> noise and AGC, wouldn't it make sense to identify your default
> CONFIG:AGCxxx setting numbers with a "dEF" to the left of the number
> when VFO A rolls over it, so that when the folks from Mount Aptos say
> to use the default AGC, that can be easily set and/or confirmed and/or
> returned to without needing to dig up the numbers somewhere?
>
> 73, Guy.
> ______________________________________________________________
> 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
>
>

Guy, K2AV

Re: K3 Receiver Noise Level -- Evaluation and Adjustment

Sigh....

Well, I must apologize, and take the flak for letting that neat piece
of information get past me. I still have to go find where that is laid
out and see what else I'm missing. I *did* go looking around for
something that told me what the defaults were before I wrote the post,
but whatever it took to find it I didn't have at the moment.

The help sentence would be:

"3. Set AGC parms to default values in CONFIG: AGC xxxx. Tap DISP in
each AGC xxxx to display <nnn> default."

The human factors guys at work would have said that a stand-alone
instruction should not require anything other than the instruction
itself to be successful.

73, Guy.
______________________________________________________________
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Sverre Holm (LA3ZA)

Re: K3 Receiver Noise Level -- Evaluation and Adjustment

In reply to this post by wayne burdick

Concerning the last few days' discussion of noise and artifacts, here is a spectral analysis plot of my K3's output: http://www.qslnet.de/member/la3za/bilder/K3-CW-spectran.jpg

First it shows the signal related artifacts in the 10-13 kHz range as mentioned by Wayne N6KR below. It also shows line noise at approximately every kHz (harmonics of 1.025-1.030 kHz). The highest of these is at approx 2050 kHz and is at about -40 dB relative to the main signal, i.e. at a level of about 10^(-40/20) = 0.01 or 1%. Thus these lines could be audible and be part of the explanation for the complaints about the K3's sound. Apart from the lines, the background is down to -60 dB above 2-3 kHz.

It is interesting to note that my spectran plot has discrete line noise as opposed to that of G4ILO in his blog from today (http://www.g4ilo.com/blog.html), plot here: http://www.g4ilo.com/uploaded_images/k3freqresponse-736797.gif . His background noise level is similar to mine.

Could this be due to differences in individual K3's as has been hinted to on this list?

My setup is:
K3 with PRE on at 14.102 MHz, RF gain at max,
CW with 400 Hz roofing filter and bandwidth set to 400 Hz,
AGC-F on and with AGC parameters SLP=9, THR=3,
I use a lot of averaging in Spectran to make the lines more visible as seen from the setup info in my plot

wayne burdick wrote

This filter rolls off everything at about 4.5
kHz, including some low-level AF sampling artifacts from 10-14 kHz
that some operators with excellent ears can hear.

Sverre, LA3ZA

K2 #2198, K3 #3391,
LA3ZA Blog: http://la3za.blogspot.com,
LA3ZA Unofficial Guide to K2 modifications: http://la3za.blogspot.com/p/la3za-unofficial-guide-to-elecraft-k2.html

John Lemay

Re: K3 Receiver Noise Level -- Evaluation and Adjustment

Hello Sverre

Thanks for putting your spectral analysis on the web page. It's very
interesting and I decided to do my own test. I used Spectrum Laboratory, but
it displays similar information to Spectran.

I have deviated from white or pink noise, because most of the time we are
listening to real signals (or qrm!). I decided to inject a signal: I used my
K3 and XG1 to perform the test. The line out from the K3 was connected to
line in on my PC.

With reference to a fundamental audio signal at 0db, a third harmonic of
this was observed at about -40, and a fifth harmonic at around -50dB. The
even order harmonics are well down in comparison.

I don't know if this is a good result or bad. But it's clear to me that if I
am listening to a 700Hz CW note, no amount of audio roll-off at 4kHz or so
is going to change the relative levels of those first few harmonics.

Just for fun, I ran the same test using an FT-847. The results were very
different. Firstly, harmonics were down at -55 or better. Secondly, the even
order products (2nd and 4th) were louder than the odd ones. And lastly, the
FT-847 graph showed several close-in spurious alongside each harmonic, which
had been completely absent with the K3.

I hope this all makes sense. And apologies if my use of technical terms is
not spot-on. I'm just an amateur, with no training in electronics or radio !

Regards

John G4ZTR

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Sverre Holm (LA3ZA)
Sent: 20 December 2009 13:13
To: [hidden email]
Subject: Re: [Elecraft] [K3] K3 Receiver Noise Level -- Evaluation and
Adjustment

Concerning the last few days' discussion of noise and artifacts, here is a
spectral analysis plot of my K3's output:
http://www.qslnet.de/member/la3za/bilder/K3-CW-spectran.jpg

First it shows the signal related artifacts in the 10-13 kHz range as
mentioned by Wayne N6KR below. It also shows line noise at approximately
every kHz (harmonics of 1.025-1.030 kHz). The highest of these is at approx
2050 kHz and is at about -40 dB relative to the main signal, i.e. at a level
of about 10^(-40/20) = 0.01 or 1%. Thus these lines could be audible and be
part of the explanation for the complaints about the K3's sound. Apart from
the lines, the background is down to -60 dB above 2-3 kHz.

It is interesting to note that my spectran plot has discrete line noise as
opposed to that of G4ILO in his blog from today
(http://www.g4ilo.com/blog.html), plot here:
http://www.g4ilo.com/uploaded_images/k3freqresponse-736797.gif . His
background noise level is similar to mine.

Could this be due to differences in individual K3's as has been hinted to on
this list?

My setup is:
K3 with PRE on at 14.102 MHz, RF gain at max,
CW with 400 Hz roofing filter and bandwidth set to 400 Hz,
AGC-F on and with AGC parameters SLP=9, THR=3,
I use a lot of averaging in Spectran to make the lines more visible as seen
from the setup info in my plot

wayne burdick wrote:
>
> This filter rolls off everything at about 4.5
> kHz, including some low-level AF sampling artifacts from 10-14 kHz
> that some operators with excellent ears can hear.
>

-----
Sverre, LA3ZA

http://www.qslnet.de/member/la3za/K2/mod.html LA3ZA Unofficial Guide to K2
modifications
--
View this message in context:
http://n2.nabble.com/K3-Receiver-Noise-Level-Evaluation-and-Adjustment-tp418
7070p4194554.html
Sent from the [K3] mailing list archive at Nabble.com.
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Julian, G4ILO

Re: K3 Receiver Noise Level -- Evaluation and Adjustment

In reply to this post by Sverre Holm (LA3ZA)

Sverre Holm (LA3ZA) wrote

Concerning the last few days' discussion of noise and artifacts, here is a spectral analysis plot of my K3's output: http://www.qslnet.de/member/la3za/bilder/K3-CW-spectran.jpg

[snip]

It is interesting to note that my spectran plot has discrete line noise as opposed to that of G4ILO in his blog from today (http://www.g4ilo.com/blog.html), plot here: http://www.g4ilo.com/uploaded_images/k3freqresponse-736797.gif . His background noise level is similar to mine.

Could this be due to differences in individual K3's as has been hinted to on this list?

You can see here http://www.g4ilo.com/images/k3-cw-400hz.jpg my attempt to replicate your plot. Note that I could only get half the resolution due to some unexplained jumping of the display when using the 44KHz or higher sample rates - I think my 5 year old shack PC can't keep up.

My original plot was made using SSB. I did note some fixed frequency spikes originally but they disappeared (lost in the noise) when I increased the LIN OUT from the usual value of 4 to 20, so I suspected that they were not being generated by the K3. I think you should try varying LIN OUT too to be sure that you aren't seeing noise from some external source.

On my CW plot there are some small fixed frequency (do not change when moving dial frequency) spikes at 2.3KHz, 3.5KHz and 4.7KHz. These presumably are generated by the K3 because they maintain their presence regardless of the LIN OUT setting.

I changed my AGC settings to the same as yours to take the plot. Changing AGC SLP has no apparent effect but increasing AGC THR increases the signal level while the spikes do not increase, so they are less prominent (particularly the 2.3KHz one) with AGC THR = 8 which is what I used when taking the plot posted on my blog. You can experiment to see this for yourself.

I have no idea what this proves, but hope eventually to learn something. What would be really interesting would be to see plots taken before and after installing a REV D DSP board.

Julian, G4ILO. K2 #392 K3 #222 KX3 #110
* G4ILO's Shack - http://www.g4ilo.com
* KComm - http://www.g4ilo.com/kcomm.html
* KTune - http://www.g4ilo.com/ktune.html

Julian, G4ILO

Re: K3 Receiver Noise Level -- Evaluation and Adjustment

In reply to this post by John Lemay

John Lemay wrote

I have deviated from white or pink noise, because most of the time we are
listening to real signals (or qrm!). I decided to inject a signal: I used my
K3 and XG1 to perform the test. The line out from the K3 was connected to
line in on my PC.

With reference to a fundamental audio signal at 0db, a third harmonic of
this was observed at about -40, and a fifth harmonic at around -50dB. The
even order harmonics are well down in comparison.

Hi John.

Thanks for posting this. It reminded me while I had Spectran set up to take a look at something that has often bugged me - the appearance of harmonically related ghost signals when using narrow filters in CW or PSK31. I used the XG1 as you did. With a wide bandwidth selected, the harmonics were lost in the noise. When using a narrow filter they can be seen quite clearly.

However - and this is the interesting bit - the level of the harmonics relative to the fundamental can be varied by changing the LIN OUT level. On my K3 reducing LIN OUT to 003 and they just about disappear. (Obviously that also depends on the strength of the input signal.)

It seems to me that there is some non-linearity in the audio stages that sets in at a fairly low level. I'm not an expert either, but might the isolating transformers in the line output be the cause of this?

Julian, G4ILO. K2 #392 K3 #222 KX3 #110
* G4ILO's Shack - http://www.g4ilo.com
* KComm - http://www.g4ilo.com/kcomm.html
* KTune - http://www.g4ilo.com/ktune.html

P.B. Christensen

Re: K3 Receiver Noise Level -- Evaluation and Adjustment

> It seems to me that there is some non-linearity in the audio stages that
> sets in at a fairly low level. I'm not an expert either, but might the
> isolating transformers in the line output be the cause of this?

Yes, see Jack Smith's work on the topic

http://www.cliftonlaboratories.com/non-linear_transformer_behavior.htm

...and the link to a fix that offers better performance:

http://www.elecraft.com/K3/mods/K3_AF_Stage_Upgrade_Instructions_Rev_B.pdf

It appears your K3 has not yet been modified although don't expect a
complete elimination of distortion products through the K3's transformers.
The problem is not lmited to the K3: distortion produced in small, datacom
transformers is dependent on the source impedance preceding the input to the
transformer.

Some folks, like K9YC, advocate the elimination of the transformers as long
as you're reasonably careful with your audio interconnection practices.

Paul, W9AC

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Julian, G4ILO

Re: K3 Receiver Noise Level -- Evaluation and Adjustment

P.B. Christensen wrote

It appears your K3 has not yet been modified although don't expect a
complete elimination of distortion products through the K3's transformers.
The problem is not lmited to the K3: distortion produced in small, datacom
transformers is dependent on the source impedance preceding the input to the
transformer.

Yes, I have performed that modification. Perhaps elimination of the transformers would be the answer.

However what this would also suggest is that the harmonic distortion products are only present on the line output, and not when someone is listening to CW on speakers or headphones. I will have to try connecting the rear speaker or headphone output to the sound card to see if the harmonics can still be observed.

Julian, G4ILO. K2 #392 K3 #222 KX3 #110
* G4ILO's Shack - http://www.g4ilo.com
* KComm - http://www.g4ilo.com/kcomm.html
* KTune - http://www.g4ilo.com/ktune.html

Joe Subich, W4TV-4

Re: K3 Receiver Noise Level -- Evaluation and Adjustment

In reply to this post by Julian, G4ILO

> However - and this is the interesting bit - the level of the
> harmonics relative to the fundamental can be varied by
> changing the LIN OUT level. On my K3 reducing LIN OUT to 003
> and they just about disappear. (Obviously that also depends
> on the strength of the input signal.)

Using Line Out is not a good representation of the audio response
to either the speaker or headphones. The Line output originates
in a different DAC (U29) than the headphone and speaker output
(U7). In addition, the differences in amplifiers, LM4950 for
the speakers and LM4811 for the headphones really means that one
must measure the specific output with the appropriate loading
(speaker or headphones) in place.

I see that Paul has already answered the low level linearity issue
with the Line output. Note as well, the transformer issue also
results in significant LF roll off starting at 1 KHz if R19 and R20
have not been changed on the KIO3 board.

73,

... Joe, W4TV

> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]] On Behalf Of Julian, G4ILO
> Sent: Sunday, December 20, 2009 11:59 AM
> To: [hidden email]
> Subject: Re: [Elecraft] [K3] K3 Receiver Noise Level --
> Evaluation and Adjustment
>
>
>
>
>
> John Lemay wrote:
> >
> > I have deviated from white or pink noise, because most of
> the time we
> > are listening to real signals (or qrm!). I decided to
> inject a signal:
> > I used my K3 and XG1 to perform the test. The line out from
> the K3 was
> > connected to line in on my PC.
> >
> > With reference to a fundamental audio signal at 0db, a
> third harmonic
> > of this was observed at about -40, and a fifth harmonic at around
> > -50dB. The even order harmonics are well down in comparison.
> >
>
> Hi John.
>
> Thanks for posting this. It reminded me while I had Spectran
> set up to take a look at something that has often bugged me -
> the appearance of harmonically related ghost signals when
> using narrow filters in CW or PSK31. I used the XG1 as you
> did. With a wide bandwidth selected, the harmonics were lost
> in the noise. When using a narrow filter they can be seen
> quite clearly.
>
> However - and this is the interesting bit - the level of the
> harmonics relative to the fundamental can be varied by
> changing the LIN OUT level. On my K3 reducing LIN OUT to 003
> and they just about disappear. (Obviously that also depends
> on the strength of the input signal.)
>
> It seems to me that there is some non-linearity in the audio
> stages that sets in at a fairly low level. I'm not an expert
> either, but might the isolating transformers in the line
> output be the cause of this?
>
> -----
> Julian, G4ILO. K2 #392 K3 #222.
> * G4ILO's Shack - http://www.g4ilo.com
> * KComm - http://www.g4ilo.com/kcomm.html
> * KTune - http://www.g4ilo.com/ktune.html
>
> --
> View this message in context:
> http://n2.nabble.com/K3-Receiver-Noise-Level-Evaluation-and-Ad

justment-tp4187070p4195177.html
Sent from the [K3] mailing list archive at Nabble.com.
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Joe Subich, W4TV-4

Re: K3 Receiver Noise Level -- Evaluation andAdjustment

In reply to this post by John Lemay

John,

Where did you make your measurements? There are significant
differences among the line, speaker and headphone outputs as
well as the IMD/harmonic performance depending on the level
of modification.

73,

... Joe, W4TV

> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]] On Behalf Of John Lemay
> Sent: Sunday, December 20, 2009 11:33 AM
> To: 'Sverre Holm (LA3ZA)'; [hidden email]
> Subject: Re: [Elecraft] [K3] K3 Receiver Noise Level --
> Evaluation andAdjustment
>
>
> Hello Sverre
>
> Thanks for putting your spectral analysis on the web page.
> It's very interesting and I decided to do my own test. I used
> Spectrum Laboratory, but it displays similar information to Spectran.
>
> I have deviated from white or pink noise, because most of the
> time we are listening to real signals (or qrm!). I decided to
> inject a signal: I used my K3 and XG1 to perform the test.
> The line out from the K3 was connected to line in on my PC.
>
> With reference to a fundamental audio signal at 0db, a third
> harmonic of this was observed at about -40, and a fifth
> harmonic at around -50dB. The even order harmonics are well
> down in comparison.
>
> I don't know if this is a good result or bad. But it's clear
> to me that if I am listening to a 700Hz CW note, no amount of
> audio roll-off at 4kHz or so is going to change the relative
> levels of those first few harmonics.
>
> Just for fun, I ran the same test using an FT-847. The
> results were very different. Firstly, harmonics were down at
> -55 or better. Secondly, the even order products (2nd and
> 4th) were louder than the odd ones. And lastly, the FT-847
> graph showed several close-in spurious alongside each
> harmonic, which had been completely absent with the K3.
>
> I hope this all makes sense. And apologies if my use of
> technical terms is not spot-on. I'm just an amateur, with no
> training in electronics or radio !
>
> Regards
>
> John G4ZTR
>
>
> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]] On Behalf Of Sverre
> Holm (LA3ZA)
> Sent: 20 December 2009 13:13
> To: [hidden email]
> Subject: Re: [Elecraft] [K3] K3 Receiver Noise Level --
> Evaluation and Adjustment
>
>
> Concerning the last few days' discussion of noise and
> artifacts, here is a spectral analysis plot of my K3's
> output: http://www.qslnet.de/member/la3za/bilder/K3-CW-spectran.jpg
>
> First it shows the signal related artifacts in the 10-13 kHz
> range as mentioned by Wayne N6KR below. It also shows line
> noise at approximately every kHz (harmonics of 1.025-1.030
> kHz). The highest of these is at approx 2050 kHz and is at
> about -40 dB relative to the main signal, i.e. at a level of
> about 10^(-40/20) = 0.01 or 1%. Thus these lines could be
> audible and be part of the explanation for the complaints
> about the K3's sound. Apart from the lines, the background is
> down to -60 dB above 2-3 kHz.
>
> It is interesting to note that my spectran plot has discrete
> line noise as opposed to that of G4ILO in his blog from today
> (http://www.g4ilo.com/blog.html), plot here:
> http://www.g4ilo.com/uploaded_images/k3freqresponse-736797.gif
> . His background noise level is similar to mine.
>
> Could this be due to differences in individual K3's as has
> been hinted to on this list?
>
> My setup is:
> K3 with PRE on at 14.102 MHz, RF gain at max,
> CW with 400 Hz roofing filter and bandwidth set to 400 Hz,
> AGC-F on and with AGC parameters SLP=9, THR=3, I use a lot of
> averaging in Spectran to make the lines more visible as seen
> from the setup info in my plot
>
>
> wayne burdick wrote:
> >
> > This filter rolls off everything at about 4.5
> > kHz, including some low-level AF sampling artifacts from 10-14 kHz
> > that some operators with excellent ears can hear.
> >
>
>
> -----
> Sverre, LA3ZA
>
> http://www.qslnet.de/member/la3za/K2/mod.html LA3ZA
> Unofficial Guide to K2 modifications
> --
> View this message in context:
> http://n2.nabble.com/K3-Receiver-Noise-Level-Evaluation-and-Ad

justment-tp418
7070p4194554.html
Sent from the [K3] mailing list archive at Nabble.com.
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Sverre Holm (LA3ZA)

Re: K3 Receiver Noise Level -- Evaluation andAdjustment

It appears that there are several sources for lines in the spectrum of the output on the LINE OUT jack.
What I measured earlier today was at a LINE level of 015, at some value above that one can see that indeed the harmonics of the signal spectrum starts to appear -maybe due to some transformer effects as mentioned on the list, but at my settings and at this line out level this is not the case. Besides, I can measure something similar from the headphone output jack.

My original measurement with signal + unrelated line noise is here:
http://www.qslnet.de/member/la3za/bilder/K3-CW-spectran.jpg

Then I measured with the RF gain set to minimum, i.e. not signal:
http://www.qslnet.de/member/la3za/bilder/K3-no-spectran.jpg

But, I cannot say for sure that the K3 is the source of the line noise (1,2,3, ... kHz) as it appears even if I unplug the minijack cable (even with the K3 turned off), however at about 15 dB lower level:
http://www.qslnet.de/member/la3za/bilder/K3-noConnect-spectran.jpg

The only way to get rid of the lines is to unplug the cable at the PC-end:
http://www.qslnet.de/member/la3za/bilder/K3-noCable-spectran.jpg

So, for sure I cannot blame these lines on the K3 now, I need to understand better their source before making any conclusions. Sorry if I have made confusion on the list with these measurements.

Sverre, LA3ZA

K2 #2198, K3 #3391,
LA3ZA Blog: http://la3za.blogspot.com,
LA3ZA Unofficial Guide to K2 modifications: http://la3za.blogspot.com/p/la3za-unofficial-guide-to-elecraft-k2.html