[Elecraft] KX3: nearby noise post-mortem

[Don Wilhelm]

Nick,

I suspect your antenna ground stakes were not connected to the utility 
entry ground rod with a #6 or larger copper wire.  The earth creates 
resistance between the antenna ground stake(s) and the AC ground in your 
home.

Now, that USB phone charger power supply connects to at least the AC 
neutral, which is in turn connected to the grounding point at the entry 
panel.  There is a lot of wire there to carry noise.  That noise can be 
induced as a voltage between your antenna ground and the electrical 
system ground due to the resistance between the different ground 
points.  That "circuit" includes your coax shield, and is then carried 
onto the board  ground and enclosure of the KX3.

I strongly suspect that is the reason the noise was not heard when you 
removed the coax shield from the KX3 is because the KX3 board and 
enclosure grounds were then isolated from that  'sneak' circuit.

This is one minor reason that all ground rods should be connected to the 
utility ground - in this case it was a noise producing inconvenience, 
but in case of a fault in your home electrical system, a dangerous 
voltage could develop between the two ground points.  Bottom line - 
connect all grounds to the utility entry ground for safety purposes, and 
hopefully it can also reduce noise generated by devices in your home in 
your received signal.  Such ground rod connections are a requirement of 
the National Electrical Code because it can be a safety hazard.

If the two grounds are more than 100 feet apart, then they do not have 
to be connected for safety (according to NEC, but consider that if your 
coax shield is connected to that remote ground stake and runs into your 
home, the same safety consideration exists between your coax shield and 
any AC grounding point, so in the case of antenna ground rods, they 
should be connected no matter what the distance.  NEC requires they be 
connected using #6 or larger wire.

Certainly with the price of copper, it is expensive to connect the 
ground rods, but what is the safety of your family or anyone who may be 
in your home worth?

73,
Don W3FPR


On 2/9/2014 8:06 PM, Nicklas Johnson wrote:
> and I pulled all the other connectors from the computer to make sure I
> wasn't getting some kind of ground loop hum.  No dice.
>
> To make matters more interesting if I backed the antenna connector halfway
> off, such that the ground was no longer connected, the hum disappeared.  I
> started worrying that I was having some trouble with the local utility, but
> decided I'd better rule out something in the house first.
>
> Through the course of troubleshooting, I came to find the culprit was a USB
> phone charger on the other side of the wall from the antenna, with the USB
> cable stretched out across the floor.  Unplugging it or disconnecting the
> USB cable mostly made the noise go away (but not entirely, though there are
> so many different power supplies and things inside the house, there could
> be multiple sources of noise, too).
>
>