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Today's Topics:
1. NI2901 receive power (emre g?ng?r)
2. Re: NI2901 receive power (Marcus M?ller)
3. Re: NI2901 receive power (Marcus D. Leech)
----------------------------------------------------------------------
Message: 1
Date: Sun, 16 Apr 2017 22:26:33 +0300
From: emre g?ng?r <[email protected]>
To: Ettus Research Support <[email protected]>,
[email protected]
Subject: [USRP-users] NI2901 receive power
Message-ID:
<cajd1uetkei46cyeu-sad8fgemf+000banhx_injrfq81von...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Hello,
I use usrp NI2901. I connect 2 horn antennas to usrp for transmit and
receive and I put a corner reflector 3m away from antenna and I measure the
results everything is okay. I also made measurements without corner
reflector, I see difference between them with network analyzer.
But when I try to analyse the received signal on gnu radio and Matlab, I
can not see difference between measurements (with corner reflector and
without corner reflector)
I mean the recived signal does not have amplitude, received power
information.
Received signal amplitude is always between -1 and 1 regardless of my gain,
high scattering obstacle usage...
What is the problem here, or how can I have received power information with
gnu radio?
Best regards.
Emre.
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Message: 2
Date: Sun, 16 Apr 2017 21:37:45 +0200
From: Marcus M?ller <[email protected]>
To: emre g?ng?r <[email protected]>, [email protected]
Subject: Re: [USRP-users] NI2901 receive power
Message-ID: <[email protected]>
Content-Type: text/plain; charset=utf-8
Dear Emre,
there's no problem here.
The complex numbers that UHD gives you are normalized between -1 and 1.
Best regards,
Marcus
On 16.04.2017 21:26, emre g?ng?r wrote:
> Hello,
>
> I use usrp NI2901. I connect 2 horn antennas to usrp for transmit and
> receive and I put a corner reflector 3m away from antenna and I
> measure the results everything is okay. I also made measurements
> without corner reflector, I see difference between them with network
> analyzer.
>
> But when I try to analyse the received signal on gnu radio and Matlab,
> I can not see difference between measurements (with corner reflector
> and without corner reflector)
> I mean the recived signal does not have amplitude, received power
> information.
> Received signal amplitude is always between -1 and 1 regardless of my
> gain, high scattering obstacle usage...
>
> What is the problem here, or how can I have received power information
> with gnu radio?
>
> Best regards.
> Emre.
>
------------------------------
Message: 3
Date: Sun, 16 Apr 2017 15:38:00 -0400
From: "Marcus D. Leech" <[email protected]>
To: [email protected]
Subject: Re: [USRP-users] NI2901 receive power
Message-ID: <[email protected]>
Content-Type: text/plain; charset=windows-1252; format=flowed
On 04/16/2017 03:26 PM, emre g?ng?r via USRP-users wrote:
> Hello,
>
> I use usrp NI2901. I connect 2 horn antennas to usrp for transmit and
> receive and I put a corner reflector 3m away from antenna and I
> measure the results everything is okay. I also made measurements
> without corner reflector, I see difference between them with network
> analyzer.
>
> But when I try to analyse the received signal on gnu radio and Matlab,
> I can not see difference between measurements (with corner reflector
> and without corner reflector)
> I mean the recived signal does not have amplitude, received power
> information.
> Received signal amplitude is always between -1 and 1 regardless of my
> gain, high scattering obstacle usage...
>
> What is the problem here, or how can I have received power information
> with gnu radio?
>
> Best regards.
> Emre.
>
>
The samples within Gnu Radio are complex-floats, and usually scaled into
{-1,+1.0}, which is what you're seeing in terms of individual samples.
Those samples are linearly-proportional to the instantaneous voltage as
seen at the antenna terminals. If you want to turn that into something that
is linearly-proportional to *power* as seen at the antenna terminals,
you should compute complex-to-mag**2 on the samples, and then low-pass
filter the result.
Now, this won't be an absolute power level, just something that is
linearly proportional to the power as seen at your antenna terminals.
If you want
*absolute* power, then you'll have to calibrate your receive setup
with calibrated signals sources, and you'll have to do so for all the
sample-rate,
gain, and frequency settings you plan to use. USRPs are not
calibrated laboratory instruments, like spectrum or network analysers.
They are
very general-purpose radios. If you want to use them for calibrated
power measurement, then you'll have to undertake your own calibration
process--that's just part of your own application of a very
general-purpose component like USRPs.
------------------------------
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