# Two Tx channels, one motherboard (N200+LFTX)

**URL:** <https://www.ruby-forum.com/t/two-tx-channels-one-motherboard-n200-lftx/233848>\
**Category:** GNU Radio\
**Created:** [January 16, 2015, 3:27pm UTC](https://www.ruby-forum.com/t/two-tx-channels-one-motherboard-n200-lftx/233848 "2015-01-16T15:27:22Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![addis\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c4cdca/32.png) [@addis\_a](https://www.ruby-forum.com/u/addis_a)\
**Post date:** [January 16, 2015, 3:27pm UTC](https://www.ruby-forum.com/t/two-tx-channels-one-motherboard-n200-lftx/233848/1 "2015-01-16T15:27:22Z")

</div>

Hi,

Is it possible to use two separate Tx channels (A:A A:B with two  
different  
center frequencies) for the N200 with the LFTX daughterboard?

I tried to do this on the Rx side and it seems to work just fine.  
However,  
on the Tx side, I am getting the following error message:

line 97, in **init**  
self.uhd\_usrp\_sink\_0.set\_subdev\_spec(“A:A A:B”, 0)  
File  
“/usr/local/lib/python2.7/dist-packages/gnuradio/uhd/uhd\_swig.py”,  
line 3447, in set\_subdev\_spec  
return \_uhd\_swig.usrp\_sink\_sptr\_set\_subdev\_spec(self, \*args,  
\*\*kwargs)  
RuntimeError: ValueError: The subdevice specification “A:A A:B” is too  
long.  
The user specified 2 channels, but there are only 1 tx dsps on mboard 0.

Thanks.

Best regards,  
Khalid