[Elecraft] K3 & flatscreen monitor noise - solved

[Paul Christensen]

> This monitor is absolutely without broadband noise emission at any 
> frequency...

Be careful when assessing noise from shack and household appliances.  I have 
had devices that raised the noise floor by several dB across the spectrum of 
the band.  The noise was so evenly broad that movement in frequency resulted 
in no change of the noise floor.  My own noise mitigation plan includes 
establishing a reference baseline on all bands using an SDR-IQ as a 
panadapter with the K3.

I first cut power to the entire house, including removal of power to 
battery-backed devices like the home security system.  With the SDR-IQ, 
screen captures can be saved and archived for later reference.  After the 
initial baseline is recorded, I then apply power to all home devices, again 
taking screen captures of the bands.   Then, one-by-one, I kill power to the 
breaker panel circuits, identifying noisy circuits.  Next, devices on the 
circuit are found.  Finally, noisy devices are worked through the addition 
of ferrite and CORCOM type CM chokes, replacement of switch-mode supplies 
with linear supplies, and in some tough cases, complete appliance 
replacement has been necessary.

In the past year, I've either modified or replaced over a dozen devices, 
most of which are small switch-mode wall warts that power my Netgear LAN 
equipment.  A few days ago I autopsied one of the Netgear wall-wart 
supplies.  There's absolutely no EMI/RFI abatement anywhere in the circuit.

The noise floor will be affected by shielding integrity of the rig and shack 
cabling as well as the type of transmission line used.  Folks bringing in 
balanced feeders to a tuner in the shack are probably most susceptible to 
home-generated noise sources.  I am using homebrewed 600-ohm line to a 
motorized balanced ATU outside the house.  CM chokes are used on the coaxial 
line portion, but a good bit of interference is being coupled onto the 
600-ohm line.  As line spacing increases, losses are minimized but noise 
ingress is inversely proportional to the benefit attained with lower line 
loss.

With the proliferation of SDR receivers, the LP-PAN unit and now the P3, 
it's easier than ever to identify and resolve noise problems within your own 
home.  Outside the boundaries of your property, more complex DF measurement 
methods must be used, but its all manageable with good technique and 
patience.

Paul, W9AC