Nearly all lower frequency noise ingress and egress is from differential
mode of different cables entering and leaving a device.
Any individual cable or wiring by itself might be common mode or
differential mode, but the nasty stuff that isn't filtered almost always is
from two or more cables or wire groups that are excited in "push-pull" at
the device.
This makes external wiring look like a big loop or big antenna system, so
even small noises can go a long distance.
The very first thing I do is get one of those multiple port lightning
arrestors or surge protectors and make sure every cable and wire leaving a
system passes through that common point and everything that can be grounded
or bonded or bypassed is bypassed with that "protector" as a common point.
73 Tom
----- Original Message -----
From: "Dennis W0JX via Topband" <topband@contesting.com>
To: <topband@contesting.com>
Sent: Thursday, September 18, 2014 3:41 PM
Subject: Topband: ROKU 3 QRM
Topbanders:
Within the last 3 to 4 months, I have been plagued with very strong QRN. I
have a two way beverage that party runs over my garage and next to the
house but it had always been an excellent performer in the past. However,
in the reverse direction the QRN was intense, well over S-9 while about
S-5 in the forward direction.
Today, I decided to track the source down. I though it might be the new
neighbors who moved in to the south since the beverage points southwest at
their home. However, I decided to start inside my own home first. I set
the QRN for S-9 on my K3 and began unplugging devices. It only took three
attempts! When I pulled the power on the relatively new ROKU 3, the noise
level on the K3 dropped from S9 to S5, about 24 db!
I then plugged in the ROKU power supply thinking it might be a switcher
but the noise did not rise so it is coming from the ROKU 3 itself. Our
previous much older original ROKU did not do this.
Now I'm going to have to deal with the XYL who is addicted to watching TV
series on the darn thing! Any ideas on how I can shield, isolate, or
modify this thing without causing a major operational issue?
By the way, the noise output of the ROKU declines with an increase in
frequency. On 80 meters, there was a slight increase in noise but not
signficantly so and no effect on 40.
Lesson learned: ALWAYS start your search inside your home first.
73, Dennis W0JX
Milan, Ohio
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