[aprssig] 8 hour Backup Power Rule

Steve Noskowicz noskosteve at yahoo.com
Mon Mar 17 22:32:47 EDT 2008

--- Robert Bruninga <bruninga at usna.edu> wrote:

> APRSdom...
> While doing emergency ham radio planning, conider the magic "8
> hour" rule being pushed by the FCC onto the cell phone
> companies.  ...snip...
> Bob, WB4APR
    This is interesting.  I retired from Motorola Sept 06 and managed two Base
site Development Engineering Validation departments -- Cellular (analog & CDMA)
& public safety / iDEN.  This is independent testing the Design to authorive
production of new base site RF equipment. 
    When in Cellular I worked with several land-line telephone companies
running cellular systems and their standard was to have 8 hours off grid.  As I
was told, this is standard in the land-line system for ceneral office
equipment.  The sites I visited had batteries, but I never thought to ask about
the A/C - or if I did, I have forgotten the answer.  
    Transmitter power is quite low in many cell sites - many under 10 watts
into 17 db gain antennas.    That 300+ amps at 24 (or 48) volts (7kW++) doesn't
all go out the antenna and, therefore, heats the site.  100 channels at 10 W
ea. is only 1kW.   Then there is the dissipation of the site control equipment
and back-haul (channel banks, microwave, T1, or fiber).  There is also
frequently other equipment and systems.
   Rich Garcia's comments are correct about the A/C problem.

   NOTE:, these systems will be useless well before the 8 hours is up - pretty
much immediately, because they will be overloaded.  The user-to-channel ratio
is somewhere around 50 in the systems I was familiar with [it's called
trunking], so only 1/50 or only 2&% of the users can get service in an
emergency.  At Northern Illinois University during the Feb shootings, many
students couldn't get service for quite a while to let their parents know they
were ok.

73, Steve

73, Steve, K9DCI

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