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Measurements >> RF Measurements >> Confusion about Resolution BW of Tx spectrum mask
https://designers-guide.org/forum/YaBB.pl?num=1247583778

Message started by AnalogAroma on Jul 14^th, 2009, 8:02am

Title: Confusion about Resolution BW of Tx spectrum mask
Post by AnalogAroma on Jul 14^th, 2009, 8:02am

Hi Everybody,

In the spec of Transmission spectrum mask ofZigbee, the power at 300K offset from fo = 868MHz should be -36 dBm/100 KHz or -86 dBm/Hz.

However, when we do PSD or FFT in Cadence Spectre or MATLAB, we get a PSD output per Hz. So, for comparison with FFT results, I should use the figure -86 dBm/Hz.

Am I right ?

Title: Re: Confusion about Resolution BW of Tx spectrum mask
Post by RFICDUDE on Jul 18^th, 2009, 11:35am

The DFT or PSD techniques also have an equivalent RBW. In principal the RBW of a DFT is equal to delta_F or 1/(Tstop-Tstart).

You would need 1 sec worth of data to yield a DFT with 1 Hz resolution per frequency bin.

1msec = 1kHz resolution

AC and PNOISE yield noise power per Hz or V I per sqrt(Hz), but the DFT and PSD functions have there own RBW.

Title: Re: Confusion about Resolution BW of Tx spectrum mask
Post by AnalogAroma on Jul 21^st, 2009, 11:40am

Hi RFICDude,

Thanks a lot for the feedback. You have helped me to avoid a huge embarassment !!!!!!!!

After applying your idea , I have found a huge discrepancy between Simulink PSD result and Cadence PSD result !!.

Tx power attenuaton in Simulink is more than -40 dBc while in Cadence using psdbb function and using RBW = 100 KHz , attenuation is -19.3dBc !

I need to contact the baseband guys to midify the RBW settings in Simulink.