TELECOM Digest OnLine - Sorted: Re: GSM-900

Re: GSM-900

Robert Bonomi (bonomi@host122.r-bonomi.com)
Thu, 24 Mar 2005 11:19:52 -0000

In article <telecom24.128.8@telecom-digest.org>,
jason <cheanglong@gmail.com> wrote:

> Hello All,

> May I know why do we need the number 900 to make GSM900 meaningful?

Because GSM is used on other frequency bands as well. <grin>

> Is it because the rf signal is in 900 MHz? or the local oscillator
> used for GSM900 system is at 900 MHz? Kindly enlighthen.

'900' is a nominal figure. neither the carrier or the LO are on
exactly 900MHz.

_Where_ the _receive_ LO is, depends on the particular set design. it
may be 'above' the desired carrier frequency, or 'below' it. it will
be offset from that desired frequency by "whatever" the IF (or 1st IF,
if multiple-state superhet) frequency is. an offset of 10.7 MHz is
common,

Of course, the _transmit_ LO will generally be on the carrier
frequency, (in _rare_ cases, the xmit LO may run on a sub-multiple,
and then be 'frequency doubled', or 'frequency tripled', before
transmission. This complicates the design, and for that reason is
"unusual", at best.)

Essentially, the number was picked because it is a "convenient"
round-number _name_, that is "approximately" accurate.

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