# How to resolve the uhd warning of sample rate

**URL:** <https://www.ruby-forum.com/t/how-to-resolve-the-uhd-warning-of-sample-rate/233257>\
**Category:** GNU Radio\
**Created:** [November 28, 2014, 8:59am UTC](https://www.ruby-forum.com/t/how-to-resolve-the-uhd-warning-of-sample-rate/233257 "2014-11-28T08:59:36Z")\
**Posts on this page:** 4\
**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:** [November 28, 2014, 8:59am UTC](https://www.ruby-forum.com/t/how-to-resolve-the-uhd-warning-of-sample-rate/233257/1 "2014-11-28T08:59:36Z")

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Dear All,

I am using USRP1 having RF daughterboards WBX (50Mhz -2.2Ghz). I have  
gone through some basic details of the USRP1 product features but dont  
know how to resolve the errors oh UHD warning saying the hardware  
doesnot support the target tx sample rate and same for the rx also.

Below is the USRP1 supported features :

ADC sample rate: 64MS/s  
DAC sample rate:128MS/s  
Host sample rate: 8 for usb2  
FPGA clock rate: 64Mhz

Please help me to understand that what value of -r i should pass for the  
both tx and for rx.

I  
have tried with -r 250e3 and 125e3 but it could not work and popping  
the warning that target tx and rx rate is not supported by hardware.

Thank you.

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**Author:** ![alok\_ranjan](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/94ad74/32.png) [@alok\_ranjan](https://www.ruby-forum.com/u/alok_ranjan)\
**Post date:** [November 28, 2014, 10:30am UTC](https://www.ruby-forum.com/t/how-to-resolve-the-uhd-warning-of-sample-rate/233257/2 "2014-11-28T10:30:34Z")

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Hi Alok,

usually, it should say something like “actual sampling rate: XXX”. What  
does it say? (actually, can you just copy&paste the whole warning?)

What program are you passing “-r” to?

Greetings,  
Marcus

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**Author:** ![alok\_ranjan](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/94ad74/32.png) [@alok\_ranjan](https://www.ruby-forum.com/u/alok_ranjan)\
**Post date:** [November 29, 2014, 4:42am UTC](https://www.ruby-forum.com/t/how-to-resolve-the-uhd-warning-of-sample-rate/233257/3 "2014-11-29T04:42:22Z")

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Hello Alok,

the problem here is that you implicitly request a lower sampling rate  
than your USRP is able to provide:  
“-r 250e3” specifies the bit rate. For “-m qam” (with a default number  
of constellation points (-p) of 16=2^4) this means that the symbol rate  
is 1/4 of that,  
(250e3 b/s) / (4 b/sym) = 62500 sym/s. Now, the default setting for  
samples per symbols (-S) is 2, so that you get 125e3 S/s, which is half  
of what you can minimally do with your USRP.  
You can either use a constellation with less points, increase your bit  
rate, or increase your samples per symbol.

Greetings,  
Marcus

PS: can you please generally reply to the mailing list and not to people  
individually? It’s a bit hard for me to keep track of this, and it might  
be really frustrating for the others that follow these lists 😉

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**Author:** ![alok\_ranjan](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/94ad74/32.png) [@alok\_ranjan](https://www.ruby-forum.com/u/alok_ranjan)\
**Post date:** [November 30, 2014, 7:47am UTC](https://www.ruby-forum.com/t/how-to-resolve-the-uhd-warning-of-sample-rate/233257/4 "2014-11-30T07:47:18Z")

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Dear Marcus,

Thank you so much for your help :). It worked fine.

Regards!  
Alok