On 05/13/2018 03:24 PM, David Bengtson via USRP-users wrote:
The Receiver Noise figure should include sampling noise and ADC ENOB.
Is that a free space path loss? You don't have any design margin for
fades/blockages etc, so an External LNA might be a good idea. 3.6 dB
NF isn't particularly low for a LNA, but it will help.
Technically, the equivalent noise figure of the ADC is "swamped" by the
gain stages ahead of the ADC.
System noise chain analysis usually (not always) gets increasingly
boring the further away from the antenna you get, because noise figures
of "deep" stages are diluted considerably by the aggregate gain of
the stages ahead of them...
On Sun, May 13, 2018 at 3:49 AM, Zhongyuan Zhao via USRP-users
<usrp-users@lists.ettus.com> wrote:
Hi,
I am trying to calculate the link budget for USRP N310.
Suppose I want a SNR of 20dB,
the signal bandwidth is 10MHz,
the thermal noise floor is -103.9dm.
Receiver noise figure is 5.8dB (N310 datasheet 5.8dB @1.8GHz)
Rx Antenna Gain 6dBi
Path loss: 120dB
Tx Antenna Gain 6dBi
RF cable Loss (RX+TX): 1dB
Then my TX power before TX antenna should be
-103.9dBm + 20dB + 5.8dB - 6dBi + 120dB -6dBi + 1dB = 30.9dBm
The receive signal strength at RX port of USRP = -78.1dBm
The noise strength at RX port of USRP = -103.9dBm
The SNR before receiver is 25.8dB, after receiver is 20dB.
However, due to the sampling noise and effective bits of ADC, I doubt that
the noise floor after the receiver would be much higher than -103.9dBm +
5.8dB = -98.1dBm, e.g. -90dBm?, in that case my receive SNR would be lower
than 20dB.
Does anyone know the output noise floor (or sensitivity) of USRP N310
receiver (e.g. RX2 port) in 500-1000MHz band? e.g. in the unit of dBm/Hz?
That would help me to decide if an external LNA is necessary. If so does
some typical wideband LNA with a gain of 20dB and noise figure of 3.6dB
would be enough.
Thank you!
Regards,
Zhongyuan Zhao
PhD Candidate,
Department of Computer Science & Engineering,
University of Nebraska-Lincoln
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