Re: [Elecraft] KX3 12kHz audio spike

[Nicklas Johnson]

Haha glad it helped you, but it  wasn't originally my idea. Credit goes to 
whomever had suggested it to me here on the list. Turning IQ on will draw 
around 10ma more power by my reading, but it's worth it not to hear that 
godawful squeal, IMHO. 

   Nick (I am still using my 3-pole LC filter when I use headphones) 

Jessie Oberreuter  wrote:

>
>On Thu, 8 Aug 2013, Nicklas Johnson wrote:
>
>> I did find that turning I/Q on reduced the spike significantly, but 
>> didn't eliminate it entirely.
>
>  Holy Cow!  That did it!  Rich!  I wonder if your dev unit had the rx 
>I/Q turned on!  Nicklas, THANK YOU!  That takes it down to the point
>where 
>I can no longer hear it!  There's still general high-freq fatigue with
>the 
>ear-buds, but that's hardly unique to the KX3, and I don't generally
>use 
>ear-buds with radios anyway.
>
>  Nicklas, you just made my day!
__
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:Elecraft@mailman.qth.net

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

Re: [Elecraft] KX3 12kHz audio spike

[Nicklas Johnson]

I decided to build a thing to work around the problem when using
headphones. I did find that turning I/Q on reduced the spike significantly,
but didn't eliminate it entirely.  I found that a pair of .47uF capacitors
and a 3mH choke did a nice job of reducing the noise over 6kHz though:

http://i.imgur.com/bAiquCc.png

I'd never built a pi-network before, so this was a decent learning exercise
too.  The reality matched up with the math quite well, I'm pleased to say.
 The spur at 12kHz went from about -59dB to -78dB, almost exactly 18dB (as
before, I'm also adding a lot of gain in the capture device to emphasize
the problem; in practice, the spur isn't anywhere near that loud).

It takes the spur at 12kHz down about 18dB, which is enough to get it well
under the noise threshold for normal listening conditions for my ears.  Of
course it would be much better if the 12kHz spur weren't there in the first
place so it wasn't necessary to try to filter it out after the fact.

One thing that's kind of interesting in the spectrum analysis is that
filtering above 6kHz looks like it emphasized the spectrum below 6kHz.  I
suspect that this is not actually what happened (given that the filter is
all passive components), but rather the filtering either slightly changed
the results of the FFT calculations, or possibly the responsiveness of the
audio capture device.  I'd be interested to hear others' theories on this
unexpected result, too.

   Nick



On 7 August 2013 10:25, David Gilbert  wrote:

>
> I didn't say that RF current in a ground plane wasn't "well-behaved",
> whatever that means.  I said that it wasn't uniform, as in uniform density.
>  It's not.
>
> 73,
> Dave   AB7E
>
>
>
> On 8/7/2013 2:10 AM, Jim Brown wrote:
>
>> On 8/6/2013 8:49 PM, David Gilbert wrote:
>>
>>> Currents most certainly do not flow uniformly in ground planes, and
>>> coupling effects can be real whenever significant gain is involved.
>>>
>>
>> Actually, what happens is that a trace above an ideal "ground plane" (the
>> ground layer)  forms a transmission line, with the return current flowing
>> in the ground plane directly below he trace -- UNLESS the ground plane
>> below the trace is broken, for example, by the circuit board layout guy
>> realizing he left something off the main layer, and putting on the ground
>> layer instead. In which case there is no longer a transmission line, the
>> return current flows wherever it can. inductance is added to the path,
>> which causes magnetic coupling to other circuits, and it forms an antenna,
>> so it can radiate, into other circuitry, or outside the box, or both.
>>
>> So the RF current in a ground plane is VERY well behaved and predictable.
>> The problems arise when the PC layout guy doesn't understand the function
>> of the ground plane, and that it CANNOT be interrupted without
>> consequences. Like zipper noise on tuning in the K3.
>>
>> 73, Jim K9YC
>> __**__**__
>> Elecraft mailing list
>> Home: 
>> http://mailman.qth.net/**mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.**htm
>> Post: mailto:elecr...@mailman.qth.**net 
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>>
>>
> __**__**__
> Elecraft mailing list
> Home: 
> http://mailman.qth.net/**mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.**htm
> Post: mailto:elecr...@mailman.qth.**net 
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>



-- 
*N6OL*
Saying something doesn't make it true.  Belief in something doesn't make it
real. And if you have to lie to support a position, that position is not
worth supporting.
__
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:Elecraft@mailman.qth.net

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

Re: [Elecraft] KX3 12kHz audio spike

[David Gilbert]

I didn't say that RF current in a ground plane wasn't "well-behaved", 
whatever that means.  I said that it wasn't uniform, as in uniform 
density.  It's not.


73,
Dave   AB7E


On 8/7/2013 2:10 AM, Jim Brown wrote:

On 8/6/2013 8:49 PM, David Gilbert wrote:
Currents most certainly do not flow uniformly in ground planes, and 
coupling effects can be real whenever significant gain is involved. 


Actually, what happens is that a trace above an ideal "ground plane" 
(the ground layer)  forms a transmission line, with the return current 
flowing in the ground plane directly below he trace -- UNLESS the 
ground plane below the trace is broken, for example, by the circuit 
board layout guy realizing he left something off the main layer, and 
putting on the ground layer instead. In which case there is no longer 
a transmission line, the return current flows wherever it can. 
inductance is added to the path, which causes magnetic coupling to 
other circuits, and it forms an antenna, so it can radiate, into other 
circuitry, or outside the box, or both.


So the RF current in a ground plane is VERY well behaved and 
predictable. The problems arise when the PC layout guy doesn't 
understand the function of the ground plane, and that it CANNOT be 
interrupted without consequences. Like zipper noise on tuning in the K3.


73, Jim K9YC
__
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:Elecraft@mailman.qth.net

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html



__
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:Elecraft@mailman.qth.net

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

Re: [Elecraft] KX3 12kHz audio spike

[Jim Brown]

On 8/6/2013 8:49 PM, David Gilbert wrote:
Currents most certainly do not flow uniformly in ground planes, and 
coupling effects can be real whenever significant gain is involved. 


Actually, what happens is that a trace above an ideal "ground plane" 
(the ground layer)  forms a transmission line, with the return current 
flowing in the ground plane directly below he trace -- UNLESS the ground 
plane below the trace is broken, for  example, by the circuit board 
layout guy realizing he left something off the main layer, and putting 
on the ground layer instead. In which case there is no longer a 
transmission line, the return current flows wherever it can. inductance 
is added to the path, which causes magnetic coupling to other circuits, 
and it forms an antenna, so it can radiate, into other circuitry, or 
outside the box, or both.


So the RF current in a ground plane is VERY well behaved and 
predictable. The problems arise when the PC layout guy doesn't 
understand the function of the ground plane, and that it CANNOT be 
interrupted without consequences. Like zipper noise on tuning in the K3.


73, Jim K9YC
__
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:Elecraft@mailman.qth.net

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

Re: [Elecraft] KX3 12kHz audio spike

[David Gilbert]

That is absolutely a real effect.  Back in the mid-70's I was a product 
engineer responsible trying to sell tuning diodes to the TV tuner 
industry.  UHF tuners in the U.S. back then were still almost all 
mechanical, and even though the rest of the world had pretty much 
already converted to electronic tuning it was a tough sell. Those RF 
engineers back then were VERY conservative but they really, really knew 
their stuff.  I remember a couple of them giving me a mini-primer on how 
they designed a mechanical tuner, and it was fascinating.  Coupling from 
the oscillator to the mixer was partially affected by current flow in 
the very heavy stamped chassis (i.e., ground) partition, and they 
described how if they needed more coupling they just punched a hole here 
and there to direct the current where it would have more effect.


It might be easy to dismiss such effects as being at VHF frequencies, 
but that would be a mistake.  Currents most certainly do not flow 
uniformly in ground planes, and coupling effects can be real whenever 
significant gain is involved.


73,
Dave   AB7E





On 8/6/2013 1:46 PM, Jim Brown wrote:


Or perhaps even a circuit layout issue. On several occasions, I've 
urged the Elecraft engineering team to attend one of Henry Ott's 
excellent EMC workshops. Henry talks about keeping track of where the 
current is flowing -- ALL of the current, not just the "intended" 
current, and he talks about the invisible schematic hidden behind the 
"ground" symbol, which is one of the most common ways we lose track of 
the return current. If, for example, the current associated with that 
12 kHz clock happens to share a return current path with an audio gain 
stage, it gets added to the audio. It's the same sort of mechanism 
that if it's at the junction of the box and the outside world we call 
a "Pin One Problem."


73, Jim K9YC


__
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:Elecraft@mailman.qth.net

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

Re: [Elecraft] KX3 12kHz audio spike

[Jim Wiley]

Ahh, that's why I love this reflector.  One always has a chance to learn 
new technical terms



On 8/6/2013 12:46 PM, Jim Brown wrote:


Horsepucky. . . . . .


__
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:Elecraft@mailman.qth.net

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

Re: [Elecraft] KX3 12kHz audio spike

[Jim Brown]

On 8/6/2013 5:51 AM, Lyle Johnson wrote:
It is always best to use headphones or external speakers that have 
limited response above 5 kHz with the KX3.  The radio will not pass 
audio information above this frequency, so the only thing wide 
response headphones or speakers will provide is additional noise. 


Horsepucky.  This is nothing more than an excuse for poor design. There 
are several possible solutions, perhaps in combination, but using lousy 
headphones or speakers is not one of them -- headphones and speakers 
with poor HF response are also likely to have very bumpy amplitude and 
phase response in midrange.


First, the audio bandwidth ought to be limited in the radio -- a few 
poles of low pass around 6 kHz would make a nice dent at 12 kHz. Second, 
if there's that much ripple, it sure sounds to me like the power supply 
is either inadequately filtered or poorly regulated, or there's 
insufficient decoupling somewhere in the audio chain.


Or perhaps even a circuit layout issue. On several occasions, I've urged 
the Elecraft engineering team to attend one of Henry Ott's excellent EMC 
workshops. Henry talks about keeping track of where the current is 
flowing -- ALL of the current, not just the "intended" current, and he 
talks about the invisible schematic hidden behind the "ground" symbol, 
which is one of the most common ways we lose track of the return 
current. If, for example, the current associated with that 12 kHz clock 
happens to share a return current path with an audio gain stage, it gets 
added to the audio. It's the same sort of mechanism that if it's at the 
junction of the box and the outside world we call a "Pin One Problem."


73, Jim K9YC
__
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:Elecraft@mailman.qth.net

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

Re: [Elecraft] KX3 12kHz audio spike

[Rich Heineck]

Nick,

I think Lyle meant to type RX I/Q, not RX ISO.  Turning on the RX I/Q 
outputs (which is accompanied by the DSP load leveling) will reduce the 
12 kHz spur by 15 to 20 dB typically.  Doing this also increases overall 
supply current by about 10 mA.


When looking at these spurs on an audio spectrum analyzer that uses a 
very narrow resolution bandwidth, they're quite prominent.  But they are 
at or below the noise in a 12 kHz (or greater) bandwidth. For quite a 
few of us we would never know they were there without the 
instrumentation.  I guess good hearing can be a blessing or a curse, 
depending on what you're listening to... :-)


73,
Rich  AC7MA


On 08/06/2013 07:41 AM, Nicklas Johnson wrote:

Lyle: I gave setting RX ISO to ON a try, and though I can see some small
changes in the spectrum analyzer, it doesn't seem to change the 12 kHz
spike or its harmonics.

Granted, my hearing is abnormally good for my age.  I can still hear up to
about 18 kHz, which is pretty unusual for an almost-38-year-old I'm told.
  Flyback transformers in old TVs and monitors are the worst thing in the
world.

I wonder if connecting a 100uF capacitor across the headphone output would
be about right to attenuate noise above 5kHz.

Johnny: I did this test by routing the headphone output of the KX3 into the
input of a Roland Quad Capture, which is effectively just a really
high-quality sound card, turned the gain on the Quad Capture up about
halfway, and sampled the audio at 192kHz, 32-bit mono into Sound Forge.
  Then I ran Sound Forge's spectrum analysis tool on the captured audio.
  You could probably perform a similar test using an ordinary sound card to
see whether you have the spike at 12kHz, but you might not see the ones at
24, 36, and 48kHz if your sound card won't sample above 48000 Hz or won't
provide enough gain.  Free tools like Audacity also provide spectrum
analysis if you don't already have something like Sound Forge.

Thanks for the input; it's nice to know at least that I'm not crazy ;-)

73,

Nick



On 6 August 2013 05:51, Lyle Johnson  wrote:


This is most likely power supply ripple from the variable loading of the
DSP, which occurs at a 12 kHz rate.

You may be able to reduce it by setting MENU:RX ISO to ON.  This increases
average current in part by preventing the DSP from "sleeping" between
tasks, thus smoothing out some of the power supply load.

It is always best to use headphones or external speakers that have limited
response above 5 kHz with the KX3.  The radio will not pass audio
information above this frequency, so the only thing wide response
headphones or speakers will provide is additional noise.  This is
particularly true if your ears haven't "aged" to provide some low-pass
function for you :-)

73,

Lyle KK7P

  While doing some tests tonight to compare the white noise of my Icom

IC-7000 to the white noise of the KX3, both having the AF gain turned all
the way down, I noticed...


__**__**__
Elecraft mailing list
Home: 
http://mailman.qth.net/**mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.**htm
Post: mailto:elecr...@mailman.qth.**net 

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html






__
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:Elecraft@mailman.qth.net

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

Re: [Elecraft] KX3 12kHz audio spike

[Nicklas Johnson]

Lyle: I gave setting RX ISO to ON a try, and though I can see some small
changes in the spectrum analyzer, it doesn't seem to change the 12 kHz
spike or its harmonics.

Granted, my hearing is abnormally good for my age.  I can still hear up to
about 18 kHz, which is pretty unusual for an almost-38-year-old I'm told.
 Flyback transformers in old TVs and monitors are the worst thing in the
world.

I wonder if connecting a 100uF capacitor across the headphone output would
be about right to attenuate noise above 5kHz.

Johnny: I did this test by routing the headphone output of the KX3 into the
input of a Roland Quad Capture, which is effectively just a really
high-quality sound card, turned the gain on the Quad Capture up about
halfway, and sampled the audio at 192kHz, 32-bit mono into Sound Forge.
 Then I ran Sound Forge's spectrum analysis tool on the captured audio.
 You could probably perform a similar test using an ordinary sound card to
see whether you have the spike at 12kHz, but you might not see the ones at
24, 36, and 48kHz if your sound card won't sample above 48000 Hz or won't
provide enough gain.  Free tools like Audacity also provide spectrum
analysis if you don't already have something like Sound Forge.

Thanks for the input; it's nice to know at least that I'm not crazy ;-)

73,

   Nick



On 6 August 2013 05:51, Lyle Johnson  wrote:

> This is most likely power supply ripple from the variable loading of the
> DSP, which occurs at a 12 kHz rate.
>
> You may be able to reduce it by setting MENU:RX ISO to ON.  This increases
> average current in part by preventing the DSP from "sleeping" between
> tasks, thus smoothing out some of the power supply load.
>
> It is always best to use headphones or external speakers that have limited
> response above 5 kHz with the KX3.  The radio will not pass audio
> information above this frequency, so the only thing wide response
> headphones or speakers will provide is additional noise.  This is
> particularly true if your ears haven't "aged" to provide some low-pass
> function for you :-)
>
> 73,
>
> Lyle KK7P
>
>  While doing some tests tonight to compare the white noise of my Icom
>> IC-7000 to the white noise of the KX3, both having the AF gain turned all
>> the way down, I noticed...
>>
> __**__**__
> Elecraft mailing list
> Home: 
> http://mailman.qth.net/**mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.**htm
> Post: mailto:elecr...@mailman.qth.**net 
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>



-- 
*N6OL*
Saying something doesn't make it true.  Belief in something doesn't make it
real. And if you have to lie to support a position, that position is not
worth supporting.
__
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:Elecraft@mailman.qth.net

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

Re: [Elecraft] KX3 12kHz audio spike

[Lyle Johnson]

This is most likely power supply ripple from the variable loading of the 
DSP, which occurs at a 12 kHz rate.


You may be able to reduce it by setting MENU:RX ISO to ON.  This 
increases average current in part by preventing the DSP from "sleeping" 
between tasks, thus smoothing out some of the power supply load.


It is always best to use headphones or external speakers that have 
limited response above 5 kHz with the KX3.  The radio will not pass 
audio information above this frequency, so the only thing wide response 
headphones or speakers will provide is additional noise.  This is 
particularly true if your ears haven't "aged" to provide some low-pass 
function for you :-)


73,

Lyle KK7P


While doing some tests tonight to compare the white noise of my Icom
IC-7000 to the white noise of the KX3, both having the AF gain turned all
the way down, I noticed...

__
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:Elecraft@mailman.qth.net

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html