[USRP-users] Isolating the grounds of LFTX and LFRX in N200

khalid.el-darymli khalid.el-darymli at mun.ca
Fri Oct 17 13:45:13 EDT 2014


Hi,

I have *two N200 *devices. One of which is used as a Tx and Rx
simultaneously and the other is only used as Rx. The LFRX and LFTX
daughterboards are used for Rx and Tx, respectively. In my present test, I
am using FMCW chirp with a BW of 50 KHz.


I noticed that if the grounds of the two N200 units are connected with each
other (e.g., through using external LNAs with a common ground) I can see
the FMCW sweeps with a power around 10 dB above the noise floor in the Rx
only N200 unit; without having nothing connected to its Rx input. I managed
to absolutely cancel out this effect through simply isolating the common
grounds between the two N200 units.

The issue I am having now is with the N200 unit that has both the LFTX and
LFRX daughterboards inside it. In this unit, I am seeing the FMCW sweeps at
the Rx (without having nothing connected to Rx) with a power of around 20
dB above the noise floor.

It seems that since the LFTX and LFRX daughterboards are plugged-in to the
same motherboard, they both share the same ground!


My question is, *how do I isolate the grounds of the LFTX and LFRX
daughterboards connected to the same N200 unit to minimize the coupling
between two of them?*

I will appreciate any help on this.

Thanks.

Best regards,
Khalid
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