I have 5 GHz commercial backhaul equipment on my property, with the 48 VDC
power feed as described by K8LX. The major noise pollution is from the
switching supplies in the backs of the antennas themselves. The 48 Volt
power must regulated and converted to lower voltages, and each of those
inverters is a small transmitter radiating their detritus all over the
place. A spectrum analyzer is probably not sensitive enough to see the
noise, but a ham's receiver sure is. Those inverters on my property are
particularly offending right in the 40 meter band, probably due to the fast
edges of the switching transistors in their inverters.
I have managed to suppress the noise substantially by placing ferrites on
the power leads as close to the electronics enclosures as possible. I doubt
a complaint about a -60 dBm noise source is going anywhere.
-Doug W6DSR
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of Steve
Maki
Sent: Sunday, February 12, 2017 08:42 AM
To: towertalk <towertalk@contesting.com>
Subject: Re: [TowerTalk] Is a cellular phone tower in the nearby vacinity a
problem for a ham?
Cell sites are generally pretty quiet. The whole site pretty much runs on
batteries. Tower top equipment is always connected via fiber data lines and
-48VDC power lines. RF amp outputs always go thru steep bandpass filters.
The battery banks in cell sites ARE charged by switching supplies, but I
often have a spectrum analyzer running while I'm working in the shelters,
and have occasionally hooked up a simple dipole to it to see what the levels
are like in there, and I haven't seen much noise pollution at all.
That said, there has been some recent equipment with design flaws. One such
case involved the surge arrestor units that are placed at the tower top that
serve as the interconnection point between the -48V trunklines and the
branch cables that go out to the radios. These units have alarm wiring that
run back down to the base equipment. The units have a multitude of indicator
LEDs, and the LEDs and/or associated circuit boards were generating wideband
noise that was being picked up in the
700 MHZ band by antennas that were only a few feet away.
It was causing noise floors in the -80 dBm range, instead of the -100 dBm
that the carriers need for LTE. The manufacturer provided retrofit boards to
cure the problem.
-Steve K8LX
On 2/11/2017 14:47 PM, Barry Merrill wrote:
> I have a major cell building with antennas on the 125 foot pylons that
> are located 420 feet to the Northwest, and as the antenna swings thru
> that azimuth there is switching noise that adds 5-10db for about 25
> degrees either side.
>
> Barry W5GN
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