[Elecraft] PX3 noise generated on KX3-2M

[David Anderson]

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 <chadwasinger at outlook.com> 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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