On 05/13/2018 04:25 PM, Zhongyuan Zhao wrote:
Thank you for the response. 3.6dB NF is not impressive however I was
considering a wideband LNA as an once-for-all solution for the entire
frequency range 50-6000MHz of N310.
Let me re-phrase the question in two different ways:
1) What is the minimal discernible signal (MDS) at the input of the
N310 receiver if no external LNA is used?
I don't think there are measured specs out there yet, but my experience
in the past with most of these radios is that the narrowband MDS is
usually better than -120dBm at max gain over most of the operating
envelope.
2) If only thermal noise is fed into the N310 receiver, (-103.9dBm for
10MHz bandwidth) what is the output power or power spectrum density
(dBm/Hz) at the output of receiver? Suppose the calibration between
dBFS and dBm is done correctly. In theory, a receiver with Noise
Figure of 5.8dB adds 5.8dB to input noise, therefore output power of
the receiver would be -98.1dBm. However I am not quite sure about if
this is applicable to near thermal noise floor. A spectrum analyzer
has a NF of 3dB but the noise floor displayed might be 20dB above the
thermal noise floor.
There is usually some non-linearity measuring very close to the noise floor.
If you have an N310 and a decent lab (I assume that the UNL electronics
lab has things like calibrated noise sources, etc), then you can answer
these
questions yourself.
I am especially interested in the band of 500-1000MHz, but answers for
other bands are helpful as well.
Many thanks!
Zhongyuan Zhao
PhD Candidate,
Department of Computer Science & Engineering,
University of Nebraska-Lincoln
Office Hour: WF 9:30-10:00am, Avery Hall 12,
Suite 117, Schorr Center,
Lincoln, Nebraska 68588-0115
On Sun, May 13, 2018 at 2:36 PM, Marcus D. Leech via USRP-users
<usrp-users@lists.ettus.com <mailto:usrp-users@lists.ettus.com>> wrote:
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
<mailto: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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