One other thing I should mention: the term cell site can be a little
ambiguous. Cell carriers share tower space with other services that
might be a little less careful with their systems. If a carrier finds
themselves impacted by pollution from a fellow tower tenant or a nearby
neighbor, they will take action. But noise that stays below 700 MHZ
won't get their attention.
When you point a 20 meter yagi at a cell tower, you're most likely
pointed at many nearby homes as well, with who knows what going on.
-Steve K8LX
On 2/12/2017 12:28 PM, Barry Merrill wrote:
I hadn't really looked close to the spectrum in a while, and hadn't really
kept notes, since it's not really a major problem; the 125KV line is ALWAYS
quiet except in rare cases of dense fog; it's the 12KV Distribution line
adjacent to and at the same elevation as my second story shack that it
the noise contributor.
On 20 with the OB16-3 at 50 feet, my IC756PROIII shows a smooth noise
floor of 10 db until I approach the 320 heading of the AT&T array.
There, I see two time periods.
There is a one to several second period with no noticeable noise increase,
and then, after a 1/2 second ramp up, there is a train of spikes that
are pretty consistent, peaking to 22db, sometimes spaced 10KHz apart,
sometimes a little closer, sliding left, for one to several seconds,
and then a 1/2 second decay back to no visible spikes for one to several
seconds, repeat.
Since it is Sunday, and I'm in a residential area away from the
interstates, seems like an occasional cell phone user passes
by and the system wakes up?
And, I can't really seem to hear those spikes, with CW 500 Hz,
my normal mode.
73
Barry, W5GN
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of Steve
Maki
Sent: Sunday, February 12, 2017 10:42 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.
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