Subject: [NEXTEL-1] Correction: CELLULAR A-BAND INTERFERENCE by the Orange County, CA. Sheriff's Department

From: [email-masked]
Date: Sat, 02 Aug 2003 04:10:29 -0400

Correction: CELLULAR A-BAND INTERFERENCE by the Orange County, CA. Sheriff's
Department

CELLULAR A-BAND INTERFERENCE
Submitted by the
Communications Division
of the Orange County Sheriff's Department
June 2003

Overview
The  Communications  Division  of  the  Orange  County  Sheriff?s  Department
(OCSD/Communications) operates and maintains a Motorola SmartZone 800 MHz radio
system using Astro digital and analog modulation.  The system provides
communications to  one  hundred  twenty-five  law  enforcement,  fire,  lifeguard
and  public works  agencies for  the  County  and  its  thirty-four  incorporated
Cities.    The  system  is divided  into  six simulcasting cells using sixty-five
800 MHz frequencies, both 806 and 821 MHz.  The frequencies are distributed across
twenty-four remote radio facilities intended to provide in-building radio coverage
over approximately 800 square miles.

Cellular Presence

There are approximately 450 cellular facilities operating at 800 MHz in Orange
County. These sites are almost evenly divided between NEXTEL, AT&T Wireless
(A-Band) and
Verizon  Wireless  (B-Band).  AT&T  and NEXTEL use TDMA while Verizon uses
CDMA.   There  are  at  least  two  other  non-800  MHz  providers  operating
within  the County.

Cellular A-Band Interference

Handheld and mobile radio communications on the Orange County system suffer A-band

degradation every day.  Based on sample tests, OCSD/Communications believes that
at least one sector of all one hundred and fifty A-band facilities cause
interference out to a radial distance of 100 feet.  At least twenty-five
facilities cause interference beyond 100 feet  and  several  facilities  have
been  observed  to  cause  problems  beyond a  quarter  of  a mile.

The interference causes partial or complete loss of reception to the handheld or
mobile users  near  the  cellular  facility.    This  occurs  mostly  to  units
operating  in  the  821  MHz band  but  has  been  frequently  observed  in the
806 MHz band.  The interference  affects both  handheld  (Motorola  XTS  3000)
and  mobile  (Motorola  Astro  Spectra)
radios  with the greatest impact to the handhelds.

OCSD/Communications  believes  that  the  primary  interference  mechanism  is
intermodulation products generated in the front-end of the receiver.  Cellular
signal levels greater  than  20  dBm  (over  20,000  uV)  have  been  recorded
at  vehicle roof  heights  at distance  of  100  feet  from  the  tower.
Non-laboratory  grade  bench testing  indicates receiver  front-end  overload
problems  to  the  XTS  3000  when  signals levels  exceed approximately 35 dBm.
Relative to other providers, OCSD/Communications receives minimal cooperation from

AT&T Wireless, the local A-Band service.

Non-A-Band Interference

OCSD/Communications  suffers  from  similar  problems  caused  by  NEXTEL  radio
facilities.  These problems impact mostly the 806 MHz frequencies.  NEXTEL has
been extremely cooperative in resolving interference.
Interference  from  Verizon  Wireless  facilities  is  extremely  rare.  Isolated
Verizon  sites have been observed to cause problems when receivers are placed on
the same horizontal plane with the transmitting  antennas,  such  as  on  a
parking  structure.  Verizon  facilities are also known to compound problems when
co-located with other 800 MHz providers.  OCSD/Communications  has  a  working
relationship  with  Verizon,  but  has never  had  to test its interference
mitigation responsiveness.

http://gullfoss2.fcc.gov/prod/ecfs/retrieve.cgi?native_or_pdf=pdf&id_document=6514287925

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