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Re: [Discuss-gnuradio] GSM spectrum: Invisible 200kHz carriers?

From: TheOperator
Subject: Re: [Discuss-gnuradio] GSM spectrum: Invisible 200kHz carriers?
Date: Fri, 3 Jun 2011 01:14:26 -0700 (PDT)

Ben Wojtowicz wrote:
> Are you saying that you are seeing 4MHz wide signals?  Or are you seeing
> ~200KHz wide signals seperated by 4MHz?I see about 200kHz wide signals
> spaced 4MHz.

Ben Wojtowicz wrote:
> If you are seeing ~200KHz wide signals spaced by 4MHz, these most likely
> are
> GSM signals.  The spec states that the spacing between adjacent channels
> is
> 200KHz, but that does not mean that an operator will place all of their
> channels next to each other.  In fact, it would be bad if they did this.
> Keep in mind that the spacing between channels is 200KHz, but the occupied
> bandwidth of a GSM signal is ~270KHz.  This means that if GSM channels are
> placed next to each other, ICI will increase significantly.  Typically
> what
> is seen is a very sparse scattering of channels across the band.Thanks for
> the explanation, this makes sense. The channels are not exactly 200kHz
> wide however (see screenshots), but according to the frequencies, they
> have to be GSM.

I used this little system along with some GUI elements:

The resulting spectrum looks like this:

Such a peak has the following shape. Most of the power is distributed within
~50kHz. Do these smaller peaks have a special meaning?
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