[USRP-users] Output range of LFRX and input range of LFTX

Marcus D. Leech mleech at ripnet.com
Tue Jul 7 09:19:00 EDT 2015


On 07/07/2015 02:33 AM, Jeon via USRP-users wrote:
> First, I'd like to transmit bipolar signal through LFTX on USRP N210.
> An additional analog circuit will be connected to the output port.
>
> Is it possible for me to guess how large peak-to-peak voltage will be 
> driven from LFTX?
> I've found that some says, '7 dBm'
> That means, does the voltage depend on bandwidth and impedance of 
> analog circuit and so on?
You might find this chart helpful:

http://ifmaxp1.ifm.uni-hamburg.de/DBM.shtml

Indeed, that +7dBm rating is at the notional circuit impedance of 50ohms.

>
> And for the second, at the receiver side, I have two options.
>
> 1. To feed a unipolar signal directly into LFRX on USRP N210.
> 2. To convert a unipoalr signal into a bipolar signal using op-amp and 
> feed it into LFRX.
>
> What value of peak-to-peak voltage is safe to the LFRX in order not to 
> burn the daughterboards?
> I need to determine the output range of analog circuit if I choose (1) 
> and I need to determine the value of op-amp gain if I choose (2).
+10dBm should be safe, but for signal-quality purposes, back that off by 
about 3dB to +7dBm.

In a 50-ohm system, that's about 1.4V P-P


>
> Regards,
> Jeon.
>
>
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