# Clock synchronization B210 **URL:** \ **Category:** GNU Radio\ **Created:** [August 29, 2014, 12:03am UTC](https://www.ruby-forum.com/t/clock-synchronization-b210/231763 "2014-08-29T00:03:55Z")\ **Posts on this page:** 2\ **Page:** 1
**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:** [August 29, 2014, 12:03am UTC](https://www.ruby-forum.com/t/clock-synchronization-b210/231763/1 "2014-08-29T00:03:55Z")
Hello all, I am using the B210 without an external 10MHz clock and without a GPSDO mounted. As expected I see a frequency and sampling time error on the captured samples. Once this sampling time error is estimated, I would like to remove this in hardware by changing the sampling clock by a small amount. Similarly once the frequency error is estimated, I would like to remove this in hardware by changing the LO frequency by a small amount. How can this be achieved in GRC? Is this by calling UHD\_tune\_req() in one of my custom blocks with the correct offset? Will this call modify the setting in the UHD source block already present in GRC Thank you Sharath ---
**Author:** ![Sharath\_A](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/58f4c7/32.png) [@Sharath\_A](https://www.ruby-forum.com/u/Sharath_A)\ **Post date:** [August 29, 2014, 2:14pm UTC](https://www.ruby-forum.com/t/clock-synchronization-b210/231763/2 "2014-08-29T14:14:37Z")
On 08/29/2014 12:02 AM, Sharath A. wrote: > How can this be achieved in GRC? Is this by calling UHD\_tune\_req() in > one of my custom blocks with the correct offset? Will this call modify > the setting in the UHD source block already present in GRC You can change the offsets in software, if that’s what you’re looking for. A tune request does not know about these offsets, if you set an LO offset, it will tune such that the LO is not on DC. So, the easiest way is to imply subtract the offset from your actual target frequency. Same goes for the master\_clock\_rate