# Connect two WBX daugterboards

**URL:** <https://www.ruby-forum.com/t/connect-two-wbx-daugterboards/205803>\
**Category:** GNU Radio\
**Created:** [April 15, 2011, 8:45pm UTC](https://www.ruby-forum.com/t/connect-two-wbx-daugterboards/205803 "2011-04-15T20:45:53Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![dubstep](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/cdc98d/32.png) [@dubstep](https://www.ruby-forum.com/u/dubstep)\
**Post date:** [April 15, 2011, 8:45pm UTC](https://www.ruby-forum.com/t/connect-two-wbx-daugterboards/205803/1 "2011-04-15T20:45:53Z")

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Hi All,

I am using two USRP N210 with WBX. Can I connect two WBX with cable  
directly? Or I need an attenuator between them. If so, what kind of  
attenuator I need.

## Thanks in advance, Brook

View this message in context:  
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Sent from the GnuRadio mailing list archive at [Nabble.com](http://Nabble.com).

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**Author:** ![Brook\_L](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/d2c977/32.png) [@Brook\_L](https://www.ruby-forum.com/u/Brook_L)\
**Post date:** [April 15, 2011, 8:57pm UTC](https://www.ruby-forum.com/t/connect-two-wbx-daugterboards/205803/2 "2011-04-15T20:57:37Z")

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On 15/04/2011 2:45 PM, Brook L. wrote:

> Hi All,
> 
> I am using two USRP N210 with WBX. Can I connect two WBX with cable  
> directly? Or I need an attenuator between them. If so, what kind of  
> attenuator I need.
> 
> Thanks in advance,  
> Brook  
> This subject comes up a _lot_.

Generally, the RX portions of all the USRP-family daughter-cards (except  
the BASIC\_RX and LF\_RX) are designed to receive  
_off-air_ signals directly from an antenna. Driving them directly  
from the TX side risks destroying the sensitive  
low-noise-amplifier (and possibly other) portions of the RX chains.  
This is true of _any_ reasonably-sensitive receiver  
that is designed for off-air signals–not just a quirk of USRP-family  
daughter-cards.

In a “from the antenna” receive chain, signals of as low as -100dBm are  
usually easily discernible, and at -40dBm are usually  
of excellent quality, depending on the signal bandwidth, modulation  
involved, receiver-side sophistication, etc, etc.

What you want to do is to make sure that the RX chain receives a signal  
of no more than about -20dBm (10 microwatts–plenty!!). So  
I’d go with a 20 to 30dB attenuator if you’re going to cable them  
together.

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<div class="post-metadata">

**Author:** ![Brook\_L](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/d2c977/32.png) [@Brook\_L](https://www.ruby-forum.com/u/Brook_L)\
**Post date:** [April 15, 2011, 9:24pm UTC](https://www.ruby-forum.com/t/connect-two-wbx-daugterboards/205803/3 "2011-04-15T21:24:11Z")

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On 04/15/2011 11:56 AM, Marcus D. Leech wrote:

> > I am using two USRP N210 with WBX. Can I connect two WBX with cable  
> > directly? Or I need an attenuator between them. If so, what kind of  
> > attenuator I need.
> 
> This subject comes up a _lot_.

Considering how often this one gets asked, might it be worthwhile to  
include a little slip of paper in the transceiver boards’ packaging that  
specifically addresses it? It wouldn’t make its way to every user, but  
it seems like a good start.