# A Clarification

**URL:** <https://www.ruby-forum.com/t/a-clarification/235058>\
**Category:** GNU Radio\
**Created:** [May 29, 2013, 12:24am UTC](https://www.ruby-forum.com/t/a-clarification/235058 "2013-05-29T00:24:35Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![alcina](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/a587f6/32.png) [@alcina](https://www.ruby-forum.com/u/alcina)\
**Post date:** [May 29, 2013, 12:24am UTC](https://www.ruby-forum.com/t/a-clarification/235058/1 "2013-05-29T00:24:35Z")

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Hi,

I would appreciate if the following are clarified regarding USRP,

1.Is it necessary to have two daughter boards in USRP1 to receive data  
at  
two different frequencies?  
2.If one daughterboard is used,can it receive the data individually and  
separately at different frequencies?

Thanks!!

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**Author:** ![manjusha](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/a183cd/32.png) [@manjusha](https://www.ruby-forum.com/u/manjusha)\
**Post date:** [May 29, 2013, 12:31am UTC](https://www.ruby-forum.com/t/a-clarification/235058/2 "2013-05-29T00:31:36Z")

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> 

It depends.

If those frequencies are separated by less than the analog bandwidth of  
a single daughtercard, then you can use the dual-DDC feature to  
pick both of those frequencies out of the larger bandwidth.  
Otherwise, you must use another card. Each daughtercard has only a  
single  
analog downconverter, and there’s only a single dual-channel ADC to  
sample the output of the card.

–  
Marcus L.  
Principal Investigator  
Shirleys Bay Radio Astronomy Consortium

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<div class="post-metadata">

**Author:** ![manjusha](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/a183cd/32.png) [@manjusha](https://www.ruby-forum.com/u/manjusha)\
**Post date:** [May 29, 2013, 12:44am UTC](https://www.ruby-forum.com/t/a-clarification/235058/3 "2013-05-29T00:44:28Z")

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Hope i am not asking a silly question…

Where can i find the "Dual -DDC"feature.Is it confined to a particular  
version.Since i don’t find it .

Thanks!

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<div class="post-metadata">

**Author:** ![manjusha](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/a183cd/32.png) [@manjusha](https://www.ruby-forum.com/u/manjusha)\
**Post date:** [May 29, 2013, 12:52am UTC](https://www.ruby-forum.com/t/a-clarification/235058/4 "2013-05-29T00:52:04Z")

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> Hope i am not asking a silly question..
> 
> Where can i find the "Dual -DDC"feature.Is it confined to a particular  
> version.Since i don’t find it .
> 
> Thanks!

For USRP1 and N2XX, you get it by default, and UHD figures out what to  
do (for the most part) based on your configuration.

For B100, you need the \_2rx FPGA image.

See the attached dual\_channel\_wbx.grc example attached.

Note that the subdev spec shows the same subdev for both channels: A:0  
A:0 in this case

And you have to use some of the magic in uhd.tune\_request() to enable  
manual setting of the RF frequency, which we simply calculate as the  
midpoint between the two desired frequencies, and then we let the  
DDCs sort things out from there.