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

[Steve Maki]

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 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.