[TowerTalk] Is a cellular phone tower in the nearby vacinity a problem for a ham?

[Barry Merrill]

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 at contesting.com] On Behalf Of Steve
Maki
Sent: Sunday, February 12, 2017 10:42 AM
To: towertalk <towertalk at 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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