[USRP-users] interpretation of received signal

Marcus D. Leech mleech at ripnet.com
Wed Oct 18 01:29:43 EDT 2017


On 10/18/2017 12:08 AM, Nirmala Soundararajan via USRP-users wrote:
> Hi all,
>
> I am trying to transmit and receive a simple 10 kHz tone using a 
> single USRP B205mini-i. The input power is 0 dbm ( The amplitude of 
> 10kHz tone being 45mV). The transmitting and receiver antenna are same 
> omnidirectional type each having 3 dbi gain. I set the transmitter 
> gain as 8 and receiver gain as 70. The carrier frequency is around 800 
> MHz. The path loss comes to around 20 db considering the fact that 
> transmitting and receiving antenna are just a foot apart. ( I took far 
> field and did not consider near field)
>
> The received spectrum shows -26 dbm. How should I interpret these results?
>
> regards
>
> Nirmala
>
How did you get -26dBm?

Unless you have painstakingly *calibrated* your USRP B205mini, and wrote 
code that converts the received data into dBm, given your carefully-derived
   calibration tables, an FFT will simply show received power relative 
to the mathematical maximum in the system.

Further, given that modulating signals in the SDR world are purely 
digital number, how did you derive a figure of 45mV of modulation?






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