Power of a 'microcell' base station in an overhead drop ceiling?

Power of a 'microcell' base station in an overhead drop ceiling?
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Subject Author Date
Power of a 'microcell' base station in an overhead drop ceiling? John Bartley 03-21-2006
Posted by John Bartley on March 21, 2006, 8:54 pm
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I'm starting to suspect RFI from a micro-cell in the overhead next to a
PA system. Randomly (sometimes 2x/day, sometimes none), a digital sound
reinforcement system overmodulates and gives "sewerpipe" sound for
around 12 seconds, then returns to normal.

Changes amps, changed mikes, still occurs.

Know there's an ATT Wireless (now Cingular) base station ('micro-cell')
within 20' of the sound rack.. in the drop-ceiling of the floor below.
I'm beginning to have dark thoughts about RF hitting a cold solder
joint in a wiring run and the demodulated result overdriving the
digital sound system.

What's peak power of a micro-cell? What would cause it to transmit at
significant power for 10 to 12 seconds, and then not, for at least a
couple of hours?

Thank you for your kind and on-topic replies.


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Posted by Henry Cabot Henhouse III on March 21, 2006, 10:43 pm
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We have a rack of TV modulators and ATSC receivers for our SMATV system,
that started to act up after Cingular upgraded the power and antenna arrays
on our roof above the rack. We had to relocate the rack and recable, which
they paid for.

It's a lot of power at 2.4 ghz!





> I'm starting to suspect RFI from a micro-cell in the overhead next to a
> PA system. Randomly (sometimes 2x/day, sometimes none), a digital sound
> reinforcement system overmodulates and gives "sewerpipe" sound for
> around 12 seconds, then returns to normal.
>
> Changes amps, changed mikes, still occurs.
>
> Know there's an ATT Wireless (now Cingular) base station ('micro-cell')
> within 20' of the sound rack.. in the drop-ceiling of the floor below.
> I'm beginning to have dark thoughts about RF hitting a cold solder
> joint in a wiring run and the demodulated result overdriving the
> digital sound system.
>
> What's peak power of a micro-cell? What would cause it to transmit at
> significant power for 10 to 12 seconds, and then not, for at least a
> couple of hours?
>
> Thank you for your kind and on-topic replies.
>



Posted by John McHarry on March 22, 2006, 11:04 pm
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On Tue, 21 Mar 2006 19:43:04 -0800, Henry Cabot Henhouse III wrote:

> We have a rack of TV modulators and ATSC receivers for our SMATV system,
> that started to act up after Cingular upgraded the power and antenna arrays
> on our roof above the rack. We had to relocate the rack and recable, which
> they paid for.
>
> It's a lot of power at 2.4 ghz!
>
I don't know the rules at 2.4GHz, but, unless you are in what is called
the "blanketing zone", they paid for that out of good will. It sounds like
you are probably within the zone.

In most cases, where out of band rf gets into unlicensed equipment it is
considered the fault of the unlicensed equipment. This is usually true,
since such equipment is very seldom shielded to withstand anything near
the allowable rf field.

Posted by DecaturTxCowboy on March 22, 2006, 9:38 am
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John Bartley wrote:
> I'm starting to suspect RFI from a micro-cell in the overhead next to a
> PA system. Randomly (sometimes 2x/day, sometimes none), a digital sound
> reinforcement system overmodulates and gives "sewerpipe" sound for
> around 12 seconds, then returns to normal.
>
> I'm beginning to have dark thoughts about RF hitting a cold solder
> joint in a wiring run and the demodulated result overdriving the
> digital sound system.

GSM cellular systems are notorious for spitting out RF that is easily
picked up by audio components. Usually its a short 2 or 3 second burst
of what might sound to a laymen as high speed Morse code (as opposed to
to white noise or the screech of a telephone modem you hear when while
making a dial up connection) perhaps once every few hours.

It comes over my laptop's speakers if my phone is within an inch of the
laptop, within a foot of my radio alarm clock on the night table, within
two feet of my desktop computer's external speakers' amplifier.

The micro-cell may be putting out higher power and longer duration and
more often data bursts.

Not likely a cold solder joint per se that functions as a demodulator
for a nearby AM broadcast band transmitter, but could be along the lines
of "miscellaneous metallic junction intermodulation" (a common phrase
used in the two-way communications industry) which *does* affect FM
two-way radio communication systems.

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other useful resources:
The Federal Communications Commission (FCC)
Telecommunications Industry Association
Electronic and Software Security Products and Services
International Telecommunication Union

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