Re: [Discuss-gnuradio] CSI in gr-ieee80211

[Surligas Manos]

I use a card from Per Vices. I do not have the option to change the 
cuttoff frequency of the
filter without flashing the firmware. As a workaround, I tuned my device 
to a different frequency (+10 MHz) and using an NCO I managed to bypass 
the power loss at the center sub-carriers.

On 03/29/2014 03:11 PM, Paul Fuxjaeger wrote:
> On 28.03.14 19:40, Surligas Manos wrote:
> > Which device did you used for receiving samples? I have noticed a same
> > phenomenon with my device, caused by a coarse implementation of a high
> > pass filter.
> The filter in the Maxim2829 in the XCVR2450 that we used can be
> configured to 0, 100Hz and 30kHz and the default is 100Hz I believe? If
> you didn't change anything there this cannot explain your problem. Any
> filter than goes above 150kHz would be a problem for the centerish
> carriers in 802.11 OFDM (~300kHz carrier spacing).
>
> what happens if you TX a sinusoid and stepwise tune the RX to slightly
> off frequencies (take note of the *actual* RX LO frequency when doing
> the sweep - the difference to that one and the TX sinusoid matters).
> Does the RX power also start to decrease as soon as you set the TX-RX
> offset smaller than 150kHz?
>
> -paul
>
> PS: as Sebastian said, the outer subcarriers being lower can be
> explained by odd decimation factors like 5 - which causes the
> digital-downconversion filter chain to change to a single CIC stage I
> believe.

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