UmTRX preselector

Sylvain Munaut 246tnt at gmail.com
Wed Aug 8 18:46:57 UTC 2012


Hi,

> Its about far-near problem (05.05 p.5.1), i.e. blocking by near mobile with
> high signal at only 600kHz offset.
> Therefore, calculated that LO noise at 600kHz offset should be around
> -140dBc/Hz to keep nominal Rx sencitivity for wanted far mobile.

Mmm, interesting, I had never thought about this.

Can you confirm my computation is the right one :

Minimum Ec/No of 8 dB, thernal noise of GSM ~ -120 dBm, so the weakest
mobile would be a -112 dBm.

The interference I see specified in 05.05 is a -26 dBm sine, so with
-140 dBc/Hz you'd get a -166 dBm 'leak' of the interference in the
signal of interest at any given position, which you need to integrate
over the entire useful bandwidth of the GSM signal ( 271 kHz -> 10 *
log10(271e3) = 54 dB ), which would give a -112 dBm noise.

Cheers,

    Sylvain




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