Topband: 160m Noise Floor

[Paul Christensen]

> "My QTH is in a suburban neighborhood surrounded by other houses. Manmade 
> noise sources in the area are producing a receive noise floor of S-9 
> across the entire 160m band. Does anyone have any suggestions on how to 
> reduce the noise?"

One device at a time.   I'm presently in the middle of an exercise to 
minimize my own noise floor.  In the last couple months, I've identified 
nearly a dozen internal sources.   Here's a partial list from memory of what 
I found:

1) Toshiba DVD Player;
2) Sony PlayStation 2;
3) Switch-mode wall-wart on my Netgear router;
4) Switch mode wall-wart on my Netgear WAP;
5) Switch-mode wall-wart on my Neatgear Ethernet gigabit switch;
6) Switch-mode supply on my Dell home office workstation;
7) Switch-mode supply on my Dell shack PC;
8) Fluorescent lamp fixture;
9) SEVERE RFI when my GE Harmony clothes washer runs (in our house, that's 
the entire weekend).

With the exception of the washer, each of the devices produces low-level 
noise and each noise source appears on different segments of the HF bands. 
But each device will raise the noise floor by a few dB at different parts of 
the HF spectrum, including 160m.  The noise not only couples to the antenna 
and open-feeder transmission line of my dipole, but it also finds its way 
directly into the transceiver (example, the shack Ethernet switch).   I use 
a homebrew motorized ATU, and the open line-to-coaxial transition occurs in 
the back yard.  The problem would be even worse if the open feeder was 
routed inside the house.

It's takes a lot of patience to pull power sources as well as throw panel 
breakers while scanning the bands, looking for noise floor signature 
differences.  Start by throwing individual panel breakers and also ensure 
that battery-baked systems (e.g., security alarms) are disengaged during 
testing.  What has made my job easier is the SDR-IQ pan adapter connected to 
my Elecraft K3.  Frankly, this whole noise tracking exercise has become an 
obsession.  My ultimate goal is to see a flat baseline on SpectraVue 
software with the SDR-IQ.  To date, I've conquered 90% of the noise.

Mitigating techniques used include replacement of all Netgear switch-mode 
wall-warts with linear packs, replaced the Fluorescent lamp ballast, and 
added #31 cores to the DVD and PlayStation line cords, using K9YC's methods.

The GE Harmony washer is a hopeless cause.  One solution found by another 
owner was to deploy something like 150+ #31 cores through the washer, and he 
even had to isolate water lines since the conductive nature of water through 
the hoses was coupling RFI onto the plumbing system.  My next washer will 
absolutely be a Samsung or LG.  Seemingly, the Koreans are the only 
manufacturers who truly "get" the RFI issue.  I have several Samsung 
wall-wart cell phone charges and not one of them exhibits switch-mode noise.

Some folks will say that their homes are RFI-free from these devices.  I'd 
be willing to bet that in many cases these devices are raising the noise 
floor and the op doesn't know it.  For example, two years ago, a neighbor 
purchased a BY-manufactured "beer fridge" to keep a six-pack nearby the TV. 
That mini fridge elevated the entire 20m noise floor by 10 dB.  The noise 
floor rise was uniform.  Many folks would ignore it, thinking there's no 
problem since the noise sounds and looks the same as the VFO is spun.

I have some noise sources that come and go from neighboring homes, but by 
far, the largest source of the noise floor rise is coming from my own QTH.

In the future, I will make every attempt to get the antennas even further 
away from the homes.  For dipoles/vees, keeping open feeders outside the 
house and bringing in coax also helps.  This may mean either installing a 
balun outside, or better still, install a motorized and balanced ATU for 
160m Dipole/Vee antennas.

Paul, W9AC


----- Original Message ----- 
From: <kd6nrp at earthlink.net>
To: <topband at contesting.com>
Sent: Wednesday, September 01, 2010 1:29 PM
Subject: Topband: 160m Noise Floor


> Good Morning:
>
>
> Regards,
>
> Brian, KD6NRP
>
>
> _______________________________________________
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>