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

[Steve Maki]

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