[time-nuts] Why/when did cell towers switch to 15 MHz?

Lux, James P james.p.lux at jpl.nasa.gov
Tue Nov 18 14:30:36 UTC 2008




On 11/17/08 7:55 PM, "N3IZN at aol.com" <N3IZN at aol.com> wrote:

>
>
> Who said 10Mhz was a standard? If it was all ham radios would have a 10 Mhz
> input to replace the internal reference.

Ham radios (or "radio boxes" in general) aren't test equipment, and don't
have external reference inputs in the first place.  Most test equipment
these days uses 10 MHz as the reference input, although, historically, 1 and
5 MHz have also been used.
>
>
> Every manufacture will have there own reference frequency. With GPSDO 10  Mhz
> is the most common, but I've seen 100 Mhz and things like 7.998 Mhz.

Interestingly, the GPS receiver itself probably does NOT use 10 MHz
internally (some frequency related to the chip rate/carrier frequency is
more common).  The 10 MHz is just because the aforementioned test equipment
uses 10MHz as an input.

>
> Lucent didn't use the 10 Mhz output on their series II products but it was
> there for a test output.
>
>> and  the usual 15 MHz Cell output.
>
> My Z3801A has a 10 MHz output.  I  thought that was normal.  It seems like a
> nice round convenient  number.
>
> So why did cell phone towers switch to 15 MHz?  Or is it  just Lucent that
> switched?
>

Probably because it was convenient for their system.  When you're ordering
hundreds of something, it doesn't add much to the cost to make the frequency
what you need, and if some other equipment has a base frequency that's
different than 10, you might save overall.

Jim




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