Re: [Discuss-gnuradio] Dynamic range of USRP2-XCVR2450

[Jorge Miguel]

Hi Marcus,

-10dBm corresponds to 100µW. With an input impedance of 100Ohms, since Pmax rms= (Vmax rms)^2 / R,   --> Vmax rms= 0.1 volt

So, if I am right the maximum theoretical voltage at the input of the ADC, if 0 dB gain is set in the transceiver (XCVR2450 in my case) and noise figure of all components were 0 dB, is 0.1 volt

However the gain of the transceiver is set to increase this [0 - 0.1] volt range to [0 - 1] volt range at the input of the ADC.

Is it right ? 

Regarding the value of the ADC SNR (72.4dB), why is it important if it doesn´t depend on the input range? (SNR= 6.02*N + 1.76)

There is something I miss......grr !

Many thanks.
Jorge.

On 24 October 2010 19:57, Marcus D. Leech <address@hidden> wrote:

On 10/24/2010 01:07 PM, Jorge Miguel wrote:
> Hello,
>
> I am trying to find out the minimum/maximun input power of the ADC
> LTC2284.
> I know that the maximum input voltage is 1 Volt, 0.707Vrms, but what
> is the input impedance? so that I can calculate the maximum input
> power as:
>
> minimum input power   (SNR ADC) = Maximun input power
> ( [(0.707)/(2^14))^2]/Rin) + 72.4 dB = Maximun input power
>
> Am I right?
>
> Many thanks,
> Jorge
>
>

I believe that it's a 100ohm balanced input.

But the daughtercards all take a 50-ohm input, and convert to a balanced
output just before the
 A/D.

With the exception of the Basic_RX and LFRX, the maximum input power for
any of the other
 daughtercards is below -10dBm.

The BASIC_RX and LFRX have a maximum input power of about +10dBm.




--

Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org