Dear Emre,
I just found your email. I'm sorry I missed it in the first place. Do you
still need all the answers, or have new problems arisen?
Best regards,
Marcus
On Mon, Apr 17, 2017 at 3:54 PM, emre güngör <emregungor1...@gmail.com>
wrote:
> Hi again,
>
> How the signal amplitudes which varies around -1 and 1 can be related with
> voltage at the antenna terminal. What represents high voltage or low
> voltage. I used corner reflector which has rcs close to 1000, that means
> received power must be x1000 when there is an corner reflextor in front of
> the antenna when compared with without corner reflector case.
>
> That means the voltage at the antenna terminal is sqrt(1000).
> But I measured this difference like x2 x3.
> I used complex to mag square as you said and I also used low pass filter.
> I could not understand logic of the low pass filter but it works as I said
> at least I can see x2 x3 times difference at power.
>
> But they can not answer my questions.
> I can list them again for better reading.
>
> 1. How can I interpret signal which varied around -1 and 1, how can it be
> related to voltage?
>
> 2. How should I choose cutoff frequency of the filter and transition width
> of the filter, how it effects?
>
> 3. Measurement not even close to theory. Why I can not take x1000 power
> with corner reflector when compared to without corner reflector case.
>
> Best wishes.
> Emre.
>
>
> 16 Nis 2017 ÖS 10:39 tarihinde "Marcus D. Leech via USRP-users" <
> usrp-users@lists.ettus.com> yazdı:
>
>> On 04/16/2017 03:26 PM, emre güngör 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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>> USRP-users@lists.ettus.com
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>>
>
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