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

Ralph A. Schmid, dk5ras ralph at schmid.xxx
Sat Oct 18 01:01:08 EDT 2014


Not the ground is the problem, but the proximity of both PCBs, and the lack of shielding. Guess it will be a bigger task to shield and isolate them, using separated devices is better.

 

Ralph.

 

From: USRP-users [mailto:usrp-users-bounces at lists.ettus.com] On Behalf Of khalid.el-darymli via USRP-users
Sent: Friday, October 17, 2014 7:45 PM
To: usrp-users at lists.ettus.com
Subject: [USRP-users] Isolating the grounds of LFTX and LFRX in N200

 

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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