Re: [Discuss-gnuradio] method to improve the detection sensitivity of USRP1 with LFRX

[Marcus D. Leech]

On 03/28/2011 06:41 PM, Yan Nie wrote:
> Dear all,
>
> I'm using LFRX to detect a -120dBm signal. According to my measurement, the 
> lowest power of signal that LFRX is able to detect is -90dBm. I tried deploy 
> a preamplifier to amplify the received signal by certain dB in order to reach 
> the -90dBm, but this turned out that noise is amplified as well and the 
> signal still merges in noise, undetectable. I also tried to set proper 
> bandwidth for the lowpass filter in order to eliminate noise and avoid the 
> signal distortion to the largest extend, but this still cannot allow this 
> weak signal be detected.
>
>
> The flow-graph of my receiver is:
>
>
> usrp_source_c --> Blackman lowpass filter --> file_sink(gr.sizeof_gr_complex)
>
>
> The signal that I wish to detect is a 13-bit Barker code with 40 us chip 
> rate. The samples frequency at receiver side is 250kHz which gives the 
> decimation rate 256. Regarding with the Blackman lowpass filter, the sampling 
> frequency for this filter is 35kHz, and the cutoff frequency is 17kHz, 
> transition_width is 0.1kHz.
>
>
> Really appreciate any of your help!
>
>
>
>   
What's the carrier frequency? 

At -120dBm, you do need a low-noise amplifier with sufficient gain to
overcome the noise of the ADC.
  Higher-noise amplifiers might indeed have the effect you're seeing. 
I've used the ERA-3 series from
  Mini-Circuits sucessfully for low-noise HF reception at around 38MHz
on a BASIC_RX.






-- 
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org