Re: [Discuss-gnuradio] ADC calibration

[Brian Padalino]

On Fri, Aug 13, 2010 at 3:17 PM, Daniel Halperin
<address@hidden> wrote:
> On Tue, 10 Aug 2010, Matt Ettus wrote:
>>
>> When using a BasicRX or LFRX with the PGA set at 0dB gain (USRP1 only),
>> +10dBm is full scale on the ADC.  On the USRP2 full scale on the ADC is full
>> scale when it gets back into gnu radio.  On the USRP1 full scale on the ADC
>> is (1.67/2) times full scale due to the gain of the CORDIC.
>>
>> +10dBm = 2Vpp = 1 Vpeak = 0.7 Vrms
>>
>> With other daughterboards you will need to calibrate at the frequency of
>> interest.
>
> Thanks, that's helpful.  However, I can't quite make the math work:
>
> P = V^2/R ; 0.01 W = (1 V)^2/R ; R = 100 Ohms.
>
> But we're using SMA connectors which are 50 Ohms right?  Or should I be
> putting 1 Vpeak I *and* 1 Vpeak Q and getting the 100 Ohms from the
> combination of the two 50 Ohm connectors?

This may be helpful:

    http://en.wikipedia.org/wiki/Alternating_current#Mathematics_of_AC_voltages

Note the usage of Vrms for power calculations and not Vpeak.

> Thanks,
> Dan
>
> (forgot to reply all first, sorry for the double-msg Matt)

Good luck.

Brian