My fellow topbanders,
I have a new noise source this season. I don't seem to be making
much progress, nor do I fully understand the issue, so I thought I
would try asking for advice.
I have a very unstable carrier wandering around between 1.820 -
1.830, plus broadband noise across all of 160m and 80m. Through
process of elimination I found the source to be a wireless access
device (Ubiquiti Bullet, see http://www.ubnt.com/bullet). Here is
what has been tried so far and the results:
There are two ethernet cables associated with this device. One runs
from a switch to the POE injector (power supply); the other from the
injector to the Bullet. I added two chokes to each cable. Each choke
consists of 13 turns on a 2.4" OD #31 toroid core. Total of 4 of
these chokes, two per cable. That reduced the noise approximately 10 dB.
I wound 12 turns of the POE injector's AC power cord on another
toroid, which reduced noise another 3 dB or so. Subsequently I added
an Array Solutions AC-7B line filter, which provided no further
noise reduction.
I wound 10 turns (best I can do with "at hand" materials) of small
diameter coax on another toroid and put that in the Bullet coax
line. This reduced noise another 2 to 3 dB. Subsequently a good
quality high pass filter has been added, which did not help at all.
The coax (20 feet of LMR-600UF and 170 feet of LDF5-50A) feeds an
enclosed 2.4 GHz yagi atop one of my towers.
Some other interesting? relevant? facts:
Disconnecting the coax from the offending device completely
eliminates the noise. Reconnecting ONLY the coax shield (no center
conductor connection) the noise comes back.
Adding a 3 dB attenuator to the coax had no affect. 6 dB attenuator,
no affect. 10 dB, still no affect.
IF and ONLY IF my toroid common-mode choke is installed in the coax
line, touching a finger to the N connector on the device silences
the noise! Touching the N connector on the outboard (antenna) side
of my choke does NOT have any affect. I have no idea what this
means! Grounding the connector/device has no affect.
The 2.4G yagi is directly off the end of one Beverage at a distance
of some 150 feet, however that Beverage does not pick up the noise.
Other Beverages which are further away and not pointing toward the
antenna or the device itself are affected by this noise. I still
need at least another 15 dB of noise reduction to get rid of it. I
cannot figure out the method of noise coupling to only certain
Beverages.
The device is located at my home, but it is not mine. I have
physical access and can add filtering, etc. but I do not have access
to device configuration.
Does anyone have any ideas? Has anyone experienced anything similar?
I guess I can work DX standing up, so I can reach to keep a finger
on that connector! :-)
73,
Paul N1BUG
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