[USRP-users] interpretation of received signal

Nirmala Soundararajan nsound1 at students.towson.edu
Wed Oct 18 12:29:16 EDT 2017


Hi Marcus,

I made a simple model using Matlab Simulink and used spectrum analyser
block to observe  the transmitted and received waveform. Since 0 dbm was
the maximum input power, I just calculated (input volatge)^2 / 2. It comes
to 0.045V.  I specified block parameters and gave different values.
Actually with 0 gain of transmitter and receiver I was getting -97  to
-105 dbm for the same input voltage 45mV.

regards

Nirmala

On Wed, Oct 18, 2017 at 3:03 AM, Neel Pandeya via USRP-users <
usrp-users at lists.ettus.com> wrote:

> Also note that at 0 dBm, you're at the maximum safe input power, so your
> received signal might be saturated.
>
> --Neel Pandeya
>
>
> On Oct 17, 2017 22:30, "Marcus D. Leech via USRP-users" <
> usrp-users at lists.ettus.com> wrote:
>
> 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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