PX3 noise generated on KX3-2M

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PX3 noise generated on KX3-2M

Chad Wasinger
Hi Group,
I wanted to post this question as it relates to noise generated by the PX3 that interferes on the KX3's 2 meter module. I seen the topic was brought up a while back but I could not find a resolution to the problem. The KX3's 2 meter module works great and is super sensitive. However, when you connect the PX3, there is a very obvious and limiting noise received on the KX3. I'm narrowed it down to just 2 meter band. I use the KX3 on 2 meters for primarily weak signal work, so this does create some major issues.
Just curious as to if there has been a solution identified to solve this problem?
Thanks,
ChadN0YK

     
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Re: PX3 noise generated on KX3-2M

GM4JJJ
This is something I had too using an external transverter for 144 MHz with my KX3 Chad.

I wrote about my experience and how better grounding of the DC socket of the PX3 to the chassis reduced the radiated noise.

Here are the details again:

Since I purchased my PX3 I have suffered from radiated noise at 144 MHz. It takes the form of various buzzy spurs evenly spaced across the band and quite easily seen on another SDR. Even with just a power connector and no other leads connected I got this QRM. I was told this was normal and had to be expected with the switched mode regulators inside the PX3.

Putting my hand near the screen of the PX3 made the noise stronger and louder, but sometimes putting pressure sideways on the DC power plug would almost eliminate it, unfortunately as soon as I released the pressure it came back again. I almost considered hiring someone to hold the plug for me while I operated the rig ;-)

Getting totally fed up with this annoying noise, especially as one of the spurs was on 144.300 the SSB calling channel, I decided today to see if I could improve the situation, and I have.

I had already checked that the DC Jack was grounded properly to the side panel. However what I hadn't appreciated is that the common of the PCB is connected to a switch in the Jack and is not directly connected to the chassis of the Jack. What was happening was the barrel of the plug was connecting to the pole of this switch and the PCB common, but only loosely to the chassis of the Jack. Movement of the plug sideways with enough pressure did connect the plug better to chassis and resulted in the noise going away. I opened up the back of the PX3 and connected the chassis part of the Jack to the PCB common side of the jack's switch by soldering a small piece of copper EMI tape across the gap. This ensures that the PCB common is stoutly connected directly to chassis at the DC Jack.

This has had the desired effect, no more intermittent  increases in spurs heard in the receiver as the leads are touched or moved, and no forest of spurs visible on the SDR when I turn on the PX3.

I can now listen to relaxing white noise on 144.300 now without having to put the notch filter on to remove the heterodyne  ;-)

The usual caveats apply, don't do this modification unless you need to, and only then if you know what you are doing, take anti static precautions, and accept that it may or will invalidate any warranty you may have with Elecraft.


73 from David GM4JJJ



73 from David GM4JJJ

> On 23 Feb 2016, at 18:06, Chad Wasinger <[hidden email]> wrote:
>
> Hi Group,
> I wanted to post this question as it relates to noise generated by the PX3 that interferes on the KX3's 2 meter module. I seen the topic was brought up a while back but I could not find a resolution to the problem. The KX3's 2 meter module works great and is super sensitive. However, when you connect the PX3, there is a very obvious and limiting noise received on the KX3. I'm narrowed it down to just 2 meter band. I use the KX3 on 2 meters for primarily weak signal work, so this does create some major issues.
> Just curious as to if there has been a solution identified to solve this problem?
> Thanks,
> ChadN0YK
>
>                        
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Re: PX3 noise generated on KX3-2M

Jim Brown-10
On Tue,2/23/2016 10:26 AM, David Anderson wrote:
> I wrote about my experience and how better grounding of the DC socket of the PX3 to the chassis reduced the radiated noise.

David,

Thanks for posting this. I've been bugging Wayne about these issues for
more than ten years, and he still hasn't gotten the message. This is a
great example of ignoring what EMC guru Henry Ott calls "the hidden
schematic lurking behind the ground symbol," and which is a primary
cause of EMC failures (RFI, hum, buzz). In the pro audio world, we call
it "the Pin One Problem," whereby cable shields fail to contact the
shielding enclosure at the point of entry, but instead go to the circuit
board, finally reaching the chassis via a path established by the whim
of the PC board layout artist.

One VERY important correction to your post.  This connection is NOT a
"ground" or "earth," it is a BOND between the cable shield and the
shielding enclosure. Or in the case of the power connector, between DC-
and the shielding enclosure. The significance of this is that without
that bond, RF can be coupled to that cable and radiated by simple
antenna action. In addition, RF can be coupled from one cable shield to
another, and from there to an input circuit.

A connection to actual EARTH is NOT part of a solution to these
problems, proper bonding IS critical to the solution. Neil Muncy,
ex-W3WJE (SK) put this quite poetically in the tutorial workshops he did
for audio professionals. Neil said, "Buy a six pack of your favorite
beer, grab a chair and a set of good binoculars, and sit at the end of
the runway of O'Hare (substitute your local airport) and CALL ME COLLECT
when you see an aircraft take off trailing a ground wire."

73, Jim K9YC
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Re: PX3 noise generated on KX3-2M

GM4JJJ
Jim,

Thanks for the correction, of course for "ground" I meant "bond", I didn't refer to "earth" because I don't have one, apart from the mandatory mains safety earth in my shack as it is upstairs and I operate VHF and above only.

I didn't use the term "pin 1 problem"  because it isn't a very descriptive teem unless you know the history of how that term came about which you have been very vocal about popularising, but it is indeed the same problem here, "common " ( have I used the correct term) of PCB not directly BONDED to the outer Metal Case.

I was rather pleased that the solution turned out to be so simple and so effective for me.

Maybe Elecraft could look into making a factory mod, it isn't difficult or costly.

73 from David GM4JJJ

> On 23 Feb 2016, at 19:37, Jim Brown <[hidden email]> wrote:
>
>> On Tue,2/23/2016 10:26 AM, David Anderson wrote:
>> I wrote about my experience and how better grounding of the DC socket of the PX3 to the chassis reduced the radiated noise.
>
> David,
>
> Thanks for posting this. I've been bugging Wayne about these issues for more than ten years, and he still hasn't gotten the message. This is a great example of ignoring what EMC guru Henry Ott calls "the hidden schematic lurking behind the ground symbol," and which is a primary cause of EMC failures (RFI, hum, buzz). In the pro audio world, we call it "the Pin One Problem," whereby cable shields fail to contact the shielding enclosure at the point of entry, but instead go to the circuit board, finally reaching the chassis via a path established by the whim of the PC board layout artist.
>
> One VERY important correction to your post.  This connection is NOT a "ground" or "earth," it is a BOND between the cable shield and the shielding enclosure. Or in the case of the power connector, between DC- and the shielding enclosure. The significance of this is that without that bond, RF can be coupled to that cable and radiated by simple antenna action. In addition, RF can be coupled from one cable shield to another, and from there to an input circuit.
>
> A connection to actual EARTH is NOT part of a solution to these problems, proper bonding IS critical to the solution. Neil Muncy, ex-W3WJE (SK) put this quite poetically in the tutorial workshops he did for audio professionals. Neil said, "Buy a six pack of your favorite beer, grab a chair and a set of good binoculars, and sit at the end of the runway of O'Hare (substitute your local airport) and CALL ME COLLECT when you see an aircraft take off trailing a ground wire."
>
> 73, Jim K9YC
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Re: PX3 noise generated on KX3-2M

Alan Bloom
In reply to this post by Jim Brown-10
I finally got around to checking this.

On 02/23/2016 11:37 AM, Jim Brown wrote:

> I've been bugging Wayne about these issues for
> more than ten years, and he still hasn't gotten the message. This is a
> great example of ignoring what EMC guru Henry Ott calls "the hidden
> schematic lurking behind the ground symbol," and which is a primary
> cause of EMC failures (RFI, hum, buzz). In the pro audio world, we call
> it "the Pin One Problem," whereby cable shields fail to contact the
> shielding enclosure at the point of entry, but instead go to the circuit
> board, finally reaching the chassis via a path established by the whim
> of the PC board layout artist.

It is not a "pin 1" problem. The metal shell of the chassis-mount power
supply connector is mounted directly to the metal side panel of the PX3
and the paint is masked around the hole to make sure it makes a good
connection.

On 02/23/2016 10:26 AM, David Anderson wrote:

 > Since I purchased my PX3 I have suffered from radiated noise at 144
 > MHz.
...
 > I had already checked that the DC Jack was grounded properly to the
 > side panel. However what I hadn't appreciated is that the common of
 > the PCB is connected to a switch in the Jack and is not directly
 > connected to the chassis of the Jack. What was happening was the
 > barrel of the plug was connecting to the pole of this switch and the
 > PCB common, but only loosely to the chassis of the Jack. Movement of
 > the plug sideways with enough pressure did connect the plug better to
 > chassis and resulted in the noise going away.

I'm trying to understand that.  The power jack has three pins, the
connector shell (tied to the printed circuit board ground plane in the
PX3), the center pin (connected to the +12V input) and a switch.  The
switch shorts to the connector shell when nothing is plugged in and
opens when a power plug is inserted.

But the thing is, the switch is not used and that pin is not connected
to anything inside the PX3.  (The only reason I used a jack with a
switch was that it was the only suitable chassis-mount type I could
find.)  Besides, that pin is internally disconnected whenever the plug
is inserted anyway.

I just confirmed all that by double-checking the PCB artwork and by
measuring an actual PX3 with an ohmmeter.  If you'd like to check it
yourself, the three connector contacts are arranged like this:  The
switch pin is the one on the side of the connector.  The +12V pin is the
one farthest from the panel.  The shield/ground pin is the one that is
almost hidden underneath the connector.

 > I opened up the back of
 > the PX3 and connected the chassis part of the Jack to the PCB common
 > side of the jack's switch by soldering a small piece of copper EMI
 > tape across the gap. This ensures that the PCB common is stoutly
 > connected directly to chassis at the DC Jack.
 >
 > This has had the desired effect, no more intermittent  increases in
 > spurs heard in the receiver as the leads are touched or moved,

I'm not sure from that description exactly what was connected to what so
it's hard to figure out how that could have affected the noise.  It
sounds like you probably connected the switch contact to the connector
shell, but I don't see how that could have affected anything since that
contact is disconnected whenever a plug is inserted and it's a
no-connect on the PC board.

You might check to make sure the mounting nut on the power connector is
good and tight and the connector body is making a solid contact to the
inside of the side panel.  I'm guessing that's the most likely cause of
the noise radiation.

Alan N1AL
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Re: PX3 noise generated on KX3-2M

GM4JJJ
Alan,

Thanks for taking the time to investigate this.


> On 27 Feb 2016, at 05:35, Alan <[hidden email]> wrote:
>
> I finally got around to checking this.
>
>>
>
> It is not a "pin 1" problem. The metal shell of the chassis-mount power supply connector is mounted directly to the metal side panel of the PX3 and the paint is masked around the hole to make sure it makes a good connection.

Agree that is the case on mine also.

>
> On 02/23/2016 10:26 AM, David Anderson wrote:
>
> > Since I purchased my PX3 I have suffered from radiated noise at 144
> > MHz.
> ...
> > I had already checked that the DC Jack was grounded properly to the
> > side panel.

First thing I checked.



> However what I hadn't appreciated is that the common of
> > the PCB is connected to a switch in the Jack and is not directly
> > connected to the chassis of the Jack.

We agree


> What was happening was the
> > barrel of the plug was connecting to the pole of this switch and the
> > PCB common, but only loosely to the chassis of the Jack.

The switch doesn’t connect to anything, BUT the contact connection to the barrel of the plug makes much better contact to switch contact spring than the regular connection.



> Movement of
> > the plug sideways with enough pressure did connect the plug better to
> > chassis and resulted in the noise going away.

This is the problem, not the connection from the socket to the chassis which is perfectly fine. It is the relatively poor connection between the plug and socket. Exerting sideways pressure decrease the contact resistance from DC return to the chassis. Note nothing to do with the tightness of the nut on the socket, that wasn’t moving and was not slack.



>
> I'm trying to understand that.  The power jack has three pins, the connector shell (tied to the printed circuit board ground plane in the PX3), the center pin (connected to the +12V input) and a switch.  The switch shorts to the connector shell when nothing is plugged in and opens when a power plug is inserted.

OK
>
> But the thing is, the switch is not used and that pin is not connected to anything inside the PX3.  (The only reason I used a jack with a switch was that it was the only suitable chassis-mount type I could find.)  Besides, that pin is internally disconnected whenever the plug is inserted anyway.

However using the unused switch contact switch is a much better connection from plug DC return and connecting that to the chassis reduced the intermittent poor contact bonding between the DC plug and the chassis.

>
> I just confirmed all that by double-checking the PCB artwork and by measuring an actual PX3 with an ohmmeter.  If you'd like to check it yourself, the three connector contacts are arranged like this:  The switch pin is the one on the side of the connector.  The +12V pin is the one farthest from the panel.  The shield/ground pin is the one that is almost hidden underneath the connector.
>
> > I opened up the back of
> > the PX3 and connected the chassis part of the Jack to the PCB common
> > side of the jack's switch by soldering a small piece of copper EMI
> > tape across the gap. This ensures that the PCB common is stoutly
> > connected directly to chassis at the DC Jack.
> >
> > This has had the desired effect, no more intermittent  increases in
> > spurs heard in the receiver as the leads are touched or moved,
>
> I'm not sure from that description exactly what was connected to what so it's hard to figure out how that could have affected the noise.  It sounds like you probably connected the switch contact to the connector shell, but I don't see how that could have affected anything since that contact is disconnected whenever a plug is inserted and it's a no-connect on the PC board.

By connecting that very good connection between the switch contact and the barrel of the DC plug to the chassis of the PX3 with a very short wide piece of copper tape the resistance from barrel to chassis was consistently low and the radiated noise was eliminated.


>
> You might check to make sure the mounting nut on the power connector is good and tight and the connector body is making a solid contact to the inside of the side panel.  I'm guessing that's the most likely cause of the noise radiation.


No, that was not the case, it was the very first thing I checked. It is purely the contact resistance from plug  outer to the socket not being good enough, and the solution was to reduce that by using the unused contact going to the switch and bonding that contact to the chassis as well. It completely eliminated the problem I had.


73

David GM4JJJ

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Re: PX3 noise generated on KX3-2M

GM4JJJ
That is how I fixed my problem then, I have connected the real common on the top of the socket to the flange which is connected to the case. I used a piece of copper tape as shown in last email photo. This stops the connection between the flange (case) and the common on the board being reliant on the plug being a tight fit in the barrel.

It all makes sense now.

Sorry if I had confused the situation with my description written from memory, but I did send photos clearly showing what I had done.  ;-)

I was adamant that this fixed a problem for me with radiated crud on 2m, especially annoying as it could be intermittent depending on how much pressure was applied sideways to the plug.

This type of connector is used in other pieces of gear, like the KX3, is there a similar pin 1 type problem as a result of the same thing I wonder Alan?

I am sure you folks at Elecraft will come up with a more elegant solution than I did. :-)

73 from David GM4JJJ

> On 27 Feb 2016, at 18:19, Alan <[hidden email]> wrote:
>
> However I did find out something that was news to me. I had to remove the power supply board from the PX3 and do some more ohmmeter measurements to discover it.  It turns out that the metal body of the connector that screws to the panel is not connected to its ground pin! In other words, there is no electrical connection between the side panel and the ground pin (PCB ground plane) when the power plug is not inserted.
>
> When the plug is inserted, the mounting flange and the ground pin are connected only through the plug's outer sleeve.  That solves the mystery of why wiggling the plug caused the radiated noise to go up and down. If the plug's sleeve does not make good contact with the connector flange, then there is a "pin 1" problem because the sleeve is grounded only via the PC board, which has a long return path to chassis ground.
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