Re: [Discuss-gnuradio] Adjacent interference problem with the USRP

[Tom Rondeau]

Mathias Coinchon wrote:
> Hello,
>
> I live near a powerful GSM/UMTS base station operating in the 900MHz, 
> 1.8GHz, 2.2 GHz bands and I have noticed that I have got problems 
> receiving signals in these bands with my USRP (using DBSRX daughterboard).
> I guess the problem comes from the fact that the interfering signal 
> from this base station comes in the A/D converter in all cases as no 
> (selectable) pre-filtering is performed depending on the decimation. 
> This is a well known problem from software radio platforms.
>
> Do anybody have any advice how I could easily solve this problem ?
>
> I am thinking to use the IF output from a scanner but the problem is 
> the bandwidth is generally limited.
>
> Are there solution for doing selectable pre-filtering (with 
> possibility to switch frequency and bandwidth) ?
>
> Thank you for your help
>
> Mathias

Mathias,

The only way around this problem is to filter out the strong signals in 
the band before you hit the LNA and ADC, at least enough so that the 
total power is within the dynamic range of the front-end.

I'd suggest trying to find or build a filter to reject the GSM bands 
you're having issues with.

This might be a good place to start although I'm sure some of the Hams 
here can suggest places with better prices:
http://www.mini-circuits.com/products/filters_coax_bandpass.html

Tom