Re: [Discuss-gnuradio] Received power measurement

[Marcus Müller]

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Hi Vanush,

good question, actually.
The point here (that I try to highlight whenever a question about
received signal strength / RSSI / RX power requirement comes up) is
that received signal strength is so much depending on what you are
trying to measure, and how you go about to do that.

Although I agree that something like a table saying "tuned to
1.284GHz, for the daughterboard YMCA in revision 42 in combination
with the onboard ADC of the ettus b430 USRP, sampling a expensively
generated noise that looks white for the complete ADC bandwidth, for
which the perfectly matched signal generator proclaims that the
accumulated power is -15dBm, should yield, given the following
combination of filter and sampling rate settings, an average magnitude
of 0.2-0.3, assuming that you have self-calibrated the USRP well
enough" can be useful - but only if your application looks similar
enough to the benchmark; which it usually won't.

These tables will be big. And of limited helpfulness - in the end, the
user has to calibrate things himself; if there is no high-end
equipment at the user's site, then there's no way to measure e.g.
matching of antennas, quality of cabling...

However: Medhat, you just said the results were "inaccurate"; maybe if
he elaborated on that, we'd know what you were trying to measure.
In fact, the results of avg_mag_sqrd are accurate to the point of
numerical accuracy if you're measuring the average numerical power of
the digital domain sample -- but I do get the feeling that is not what
you're trying to do.

Greetings,
Marcus

On 26.03.2014 13:29, Vanush Vaswani wrote:
> Is there any reason that this isn't done at a few frequencies
> during manufacturing and provided in the datasheet? I've noticed
> this with a few SDR's. Surely, it would provide a ballpark figure
> for those who could not afford expensive test equipment.
> 
> 
> On Wed, Mar 26, 2014 at 11:21 PM, Marcus D. Leech
> <address@hidden> wrote:
> 
>> On 03/26/2014 07:04 AM, Medhat Hamdy wrote:
>> 
>> Hi all,
>> 
>> I need to know if there is any method to measure the received
>> signal power using USRP N210. I am using
>> gr_probe_avg_mag_sqrd_x_0 to measure the signal strength,
>> however, the results are not accurate.
>> 
>> Thanks
>> 
>> 
>> 
>> 
>> _______________________________________________ Discuss-gnuradio
>> mailing
>> address@hidden://lists.gnu.org/mailman/listinfo/discuss-gnuradio
>>
>>
>> 
To get accurate readings, you have to calibrate with an external, known,
>> source.
>> 
>> 
>> 
>> _______________________________________________ Discuss-gnuradio
>> mailing list address@hidden 
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>> 
>> 
> 
> 
> 
> _______________________________________________ Discuss-gnuradio
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