[K3] Noise from P3

[John Lemay]

Interesting !

I'll try some more ferrite tomorrow .........

John

-----Original Message-----
From: David Pratt [mailto:[hidden email]]
Sent: 23 March 2011 21:31
To: Ken Roberson; John Lemay
Cc: [hidden email]; [hidden email]
Subject: Re: [Elecraft] [K3] Noise from P3

*** Thank you to everyone for their kind help. ***

I am pleased to report that putting a ferrite 'clamp-on' core at each
end of the 12V power lead has completely cured the problem.  Because the
cable is quite thin, I managed to wind two turns round each core.

I wonder whether a screened power cable might have been an alternative
answer?  Maybe I shall try that tomorrow.

Incidentally, before fitting the cores I did notice that placing a
finger near the screen did increase the noise.

73 de David G4DMP
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[Jim Brown-10]

On 3/23/2011 1:30 PM, John Lemay wrote:
> Yes, I can "home in" on the noise with great certainty !

That indicates that the noise is being radiated by the P3 or something
attached to it, and picked up on your antenna (and not picked up on K3
wiring).

The comments by others that ferrites on the power cable killed the noise
suggest that that cable is doing the radiating. Now, I wouldn't rule out
the coax as a radiator if someone has choked the power cable and still
heard noise -- with RFI, always assume that there could be more than one
coupling mechanism.

Again, let me emphasize that a ferrite core is a low Q parallel resonant
circuit. Most single #31 or #43 cores are, by virtue of their size and
shape, cause a single turn to resonate close to 2M, while more turns
move the resonance down to lower frequencies. This a problem on 2M is
better solved with multiple cores rather than multiple turns, whereas
problems on 6M are better solved with two turns and on the HF bands with
more turns.

73, Jim K9YC
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[Alan Bloom]

On Wed, 2011-03-23 at 19:35 -0700, Jim Brown wrote:
> On 3/23/2011 1:30 PM, John Lemay wrote:
> > Yes, I can "home in" on the noise with great certainty !
>
> That indicates that the noise is being radiated by the P3 or something
> attached to it, and picked up on your antenna (and not picked up on K3
> wiring).

I can see the noise on mine if I hook a clip lead to the ANT3 (144 MHz)
connector and place it close to the display.  But I doubt you could hear
that on an external antenna.  The opening in the front panel is much
smaller than 1/2 wavelength on 2 meters, so the far field should be
greatly attenuated and the near field falls off rapidly with distance.

> The comments by others that ferrites on the power cable killed the noise
> suggest that that cable is doing the radiating. Now, I wouldn't rule out
> the coax as a radiator if someone has choked the power cable and still
> heard noise -- with RFI, always assume that there could be more than one
> coupling mechanism.

The shells of the coax and the RS-232 connectors are grounded directly
to the chassis.  Sounds like it must be the power cable.

Alan N1AL

> Again, let me emphasize that a ferrite core is a low Q parallel resonant
> circuit. Most single #31 or #43 cores are, by virtue of their size and
> shape, cause a single turn to resonate close to 2M, while more turns
> move the resonance down to lower frequencies. This a problem on 2M is
> better solved with multiple cores rather than multiple turns, whereas
> problems on 6M are better solved with two turns and on the HF bands with
> more turns.
>
> 73, Jim K9YC
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>

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[David Pratt]

In a recent message, Alan Bloom <[hidden email]> writes

>The shells of the coax and the RS-232 connectors are grounded directly
>to the chassis.  Sounds like it must be the power cable.

That being so, Alan, is there any value in supplying screened cable for
the power lead rather than the twin 'bell wire' used at present?

73 de David G4DMP
--
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 | David M Pratt, Kippax, Leeds.   |
 | Website: http://www.g4dmp.co.uk |
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[Alan Bloom]

On Thu, 2011-03-24 at 04:39 +0000, David Pratt wrote:
> In a recent message, Alan Bloom <[hidden email]> writes
>
> >The shells of the coax and the RS-232 connectors are grounded directly
> >to the chassis.  Sounds like it must be the power cable.
>
> That being so, Alan, is there any value in supplying screened cable for
> the power lead rather than the twin 'bell wire' used at present?

Maybe a little, but I suspect that wrapping a few turns through a
ferrite core would be much more effective.

Alan


> 73 de David G4DMP


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[Jim Brown-10]

On 3/23/2011 9:39 PM, David Pratt wrote:
> That being so, Alan, is there any value in supplying screened cable for
> the power lead rather than the twin 'bell wire' used at present?

Not if it is common mode current, coupled from signal common onto the V-
wire. Go to my website and study the material on "The Pin One Problem."  
While it is written about audio interconnects, it applies directly here
to the V- lead.

http://audiosystemsgroup.com/publish.htm

Shielding only matters with respect to DIFFERENTIAL circuit (that is,
RFI between V+ and V-).

73, Jim K9YC


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[John Lemay]

Well, I have undertaken a lot of work to address this problem:-

1. taken apart the P3 and doubly made certain that contact between the
various chassis parts is good.

2. taken apart the K3 and paid particular attention to the contact areas
around the rear panel and IF output area.

3. placed ferrites at both ends of the DC lead to the P3.

4. used the P3 on a separate power supply.

5. placed ferrites on the IF lead between the P3 and K3.

The problem remains. In fact if anything it is a little worse this morning,
but these are not lab measurements.

So, Dxing on 2m with the P3 running is a non-starter for me.

John G4ZTR


-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Jim Brown
Sent: 24 March 2011 06:03
To: [hidden email]
Subject: Re: [Elecraft] [K3] Noise from P3

On 3/23/2011 9:39 PM, David Pratt wrote:
> That being so, Alan, is there any value in supplying screened cable for
> the power lead rather than the twin 'bell wire' used at present?

Not if it is common mode current, coupled from signal common onto the V-
wire. Go to my website and study the material on "The Pin One Problem."  
While it is written about audio interconnects, it applies directly here
to the V- lead.

http://audiosystemsgroup.com/publish.htm

Shielding only matters with respect to DIFFERENTIAL circuit (that is,
RFI between V+ and V-).

73, Jim K9YC


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[Jim Brown-10]

On 3/24/2011 1:04 AM, John Lemay wrote:
> In fact if anything it is a little worse this morning,
> but these are not lab measurements.

FWIW -- the P3 display is a VERY good indicator of voltage at the IF,
and you can easily set it to read out in dB, and with very high resolution.

I'd say take it up with Elecraft. It should not be thus. :)  I'll bet
this thread has already gotten their attention. N1AL is on the P3 design
team, and has been following it.  Wayne and Eric both pay attention to
this list.

73, Jim K9YC
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[G3TCT]

On 19:59, John Lemay wrote:
> Well, I have undertaken a lot of work to address this problem:-
>
>    
John have you tried disconnecting the RS232 connection between K3 and P3?

Graham
G3TCT
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[K5SM]

No apparent noise from the P3 on 144.225 here, either.  The P3 is
resting against the "feet" on the right side of the K3. My antenna is
100' away at 65' and was pointing at the shack.

Bob K5SM
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[John Lemay]

Hi Graham

Yes. With or without that cable seems to make no difference.

Regards

John G4ZTR

-----Original Message-----
From: Graham Kimbell G3TCT [mailto:[hidden email]]
Sent: 24 March 2011 20:49
To: John Lemay
Cc: [hidden email]
Subject: Re: Re: [Elecraft] [K3] Noise from P3

On 19:59, John Lemay wrote:
> Well, I have undertaken a lot of work to address this problem:-
>
>    
John have you tried disconnecting the RS232 connection between K3 and P3?

Graham
G3TCT

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