# Reference Clock power level for Ettus N210 **URL:** \ **Category:** GNU Radio\ **Created:** [April 23, 2014, 3:09pm UTC](https://www.ruby-forum.com/t/reference-clock-power-level-for-ettus-n210/240617 "2014-04-23T15:09:04Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![Detlef\_R](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/58f4c7/32.png) [@Detlef\_R](https://www.ruby-forum.com/u/Detlef_R)\ **Post date:** [April 23, 2014, 3:09pm UTC](https://www.ruby-forum.com/t/reference-clock-power-level-for-ettus-n210/240617/1 "2014-04-23T15:09:04Z")
Hi, I’m using a USRP N210 and I need a 10 MHz reference clock. From [ettus.com](http://ettus.com) I got: " Ref Clock - 10 MHz Using an external 10 MHz reference clock, a square wave will offer the best phase noise performance, but a sinusoid is acceptable. The reference clock requires the following power level: USRP2 5 to 15 dBm N2XX 0 to 15 dBm " So in my case (N210) I should have a minimum 0 dBm signal. Can someone confirm this information (N2XX 0 to 15 dBm) for N210? The bad news for me is I have a -15dBm 10 MHz available… Thank you, Antonio ---
**Author:** ![panto](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/f9ae1b/32.png) [@panto](https://www.ruby-forum.com/u/panto)\ **Post date:** [April 23, 2014, 3:32pm UTC](https://www.ruby-forum.com/t/reference-clock-power-level-for-ettus-n210/240617/2 "2014-04-23T15:32:42Z")
Hi, looking at the N200 schematics from [files.ettus.com](http://files.ettus.com), I’d say: stick to the 0dBm, your clock signal has to pass a transformer and some safety/matching circuitry and still ought to be more accurate than the on-board VCTCXO; the clock multiplexer ([http://www.micrel.com/index.php/en/products/clock-timing/clock-data-distribution/multiplexers/article/29-sy89545l.html](http://www.micrel.com/index.php/en/products/clock-timing/clock-data-distribution/multiplexers/article/29-sy89545l.html)) datasheet says it needs at least a voltage swing of 0.1V after that. I’m not very much of a circuits person, but I think you won’t deteriorate much of your clock accuracy by using a clock buffer, which are quite inexpensive (if you need but one and are not afraid to solder… TI gives away samples for free). Then again, you’re trying to achieve a better clock performance than the on-board 10MHz ref clock, so I guess you shouldn’t start introducing cheap hardware in the clock signal path… Greetings, Marcus PS: maybe the removed\_email\_address@domain.invalid mailing list is better suited for this… I’ve added that to CC: ---
**Author:** ![panto](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/f9ae1b/32.png) [@panto](https://www.ruby-forum.com/u/panto)\ **Post date:** [April 23, 2014, 3:45pm UTC](https://www.ruby-forum.com/t/reference-clock-power-level-for-ettus-n210/240617/3 "2014-04-23T15:45:06Z")
Thank you Marcus, I will wait for some answers from removed\_email\_address@domain.invalid before proceeding. Best regards, Antonio ---
**Author:** ![panto](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/f9ae1b/32.png) [@panto](https://www.ruby-forum.com/u/panto)\ **Post date:** [April 23, 2014, 3:55pm UTC](https://www.ruby-forum.com/t/reference-clock-power-level-for-ettus-n210/240617/4 "2014-04-23T15:55:44Z")
We posted those numbers because they are the numbers we know will work reliably. -15dBm is unlikely to work well, but you won’t damage anything by trying. Matt On Wed, Apr 23, 2014 at 3:43 PM, Antonio P. ---
**Author:** ![panto](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/f9ae1b/32.png) [@panto](https://www.ruby-forum.com/u/panto)\ **Post date:** [April 23, 2014, 4:39pm UTC](https://www.ruby-forum.com/t/reference-clock-power-level-for-ettus-n210/240617/5 "2014-04-23T16:39:24Z")
On 04/23/2014 09:07 AM, Antonio P. wrote: > reference clock requires the following power level: > Antonio > > * * * > > Discuss-gnuradio mailing list > [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) > [Discuss-gnuradio Info Page](https://lists.gnu.org/mailman/listinfo/discuss-gnuradio) Yup, the minimum is 0dBm. – Marcus L. Principal Investigator Shirleys Bay Radio Astronomy Consortium > **[Live Draw HK Tercepat | Result HK | HK Pools | Live HK | HK Prize Hari Ini](https://www.sbrac.org)** > > Temukan live draw hk tercepat melalui halaman hk pools yang resmi dan dapatkan result hk prize melalui live hk secara langsung di situs kami. ---
**Author:** ![panto](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/f9ae1b/32.png) [@panto](https://www.ruby-forum.com/u/panto)\ **Post date:** [April 23, 2014, 5:39pm UTC](https://www.ruby-forum.com/t/reference-clock-power-level-for-ettus-n210/240617/6 "2014-04-23T17:39:00Z")
On Wed, 23 Apr 2014 15:07:52 +0200 Antonio P. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Using an external 10 MHz reference clock, a square wave will offer the > best phase noise performance, but a sinusoid is acceptable. The difference between the phase noise of a square wave and a sinus input is negligible in a radio application. Your system will be dominated by the noise of your input. Unless you are doing detection with very long integration time (in the order of seconds and longer). And even there i’m not sure whether it’s not still the input noise that’s dominating the performance instead of your reference clock noise. And in that case you care more about close in phase noise which is dominated by non-linear mixing of low frequency noise sources into your signal, than what we commonly refere to as jitter. To get that down you want to: 1. use sinusoidal input and not square wave Square wave has high frequency components, depending on the squaring buffer you will have considerable spectral components between 100MHz and 1GHz.. or even more. Cables have worse and worse characteristics the higher you go. Also small impedance mismatches will lead to more severe reflections the higer the frequency is. Also as the temperature changes, you will have changing phase shifts for different frequency components (cables are non-linear in that regard). 2. Change the clock multiplexer (SY89545) from a LVDS-\>LVDS type to a pure analog part. Or rather, remove it completely and go directly onto the AD9510 But that’s only the case if and only if you care about long integration times and the 10th decimal point of performance. For all else. Using a good quartz oscillator is more than good enough and you dont need to care about anything but having approximately the right signal levels. – The trouble with you, Shev, is you don’t say anything until you’ve saved up a whole truckload of damned heavy brick arguments and then you dump them all out and never look at the bleeding body mangled beneath the heap – Tirin, The Dispossessed, U. Le Guin ---
**Author:** ![panto](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/f9ae1b/32.png) [@panto](https://www.ruby-forum.com/u/panto)\ **Post date:** [April 23, 2014, 5:46pm UTC](https://www.ruby-forum.com/t/reference-clock-power-level-for-ettus-n210/240617/7 "2014-04-23T17:46:41Z")
On Wed, 23 Apr 2014 17:37:44 +0200 Attila K. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > For all else. Using a good quartz oscillator is more than good enough > and you dont need to care about anything but having approximately the > right signal levels. Let me give you a bit more information here. According to the N210 schematics, the clock’s PLL has a BW of 3kHz. This means that noise beyond 3kHz is dominated by the VCXO on board. Noise blow 3kHz is dominated by the reference clock. This means, that if you can keep the noise of the reference clock low at frequencies lower than 3kHz, then you will have good performance. Depending on what you use as refernce clock, you have to identify the noise sources and their properties and then work on those that have most impact on your performance. ``` Attila K. ``` – The trouble with you, Shev, is you don’t say anything until you’ve saved up a whole truckload of damned heavy brick arguments and then you dump them all out and never look at the bleeding body mangled beneath the heap – Tirin, The Dispossessed, U. Le Guin ---
**Author:** ![panto](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/f9ae1b/32.png) [@panto](https://www.ruby-forum.com/u/panto)\ **Post date:** [April 23, 2014, 4:42pm UTC](https://www.ruby-forum.com/t/reference-clock-power-level-for-ettus-n210/240617/8 "2014-04-23T16:42:22Z")
On 04/23/2014 09:31 AM, Marcus M. wrote: > solder… TI gives away samples for free). > Then again, you’re trying to achieve a better clock performance than > the on-board 10MHz ref clock, so I guess you shouldn’t start > introducing cheap hardware in the clock signal path… > > Greetings, > Marcus > > PS: maybe the [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) mailing list is better suited > for this… I’ve added that to CC: I think the main thing to watch out for with clock buffers is their linearity, since low-level non-linearity effects can increase phase-noise. Perhaps not a lot, but a little. I’d use a clock buffer, and see. – Marcus L. Principal Investigator Shirleys Bay Radio Astronomy Consortium > **[Live Draw HK Tercepat | Result HK | HK Pools | Live HK | HK Prize Hari Ini](https://www.sbrac.org)** > > Temukan live draw hk tercepat melalui halaman hk pools yang resmi dan dapatkan result hk prize melalui live hk secara langsung di situs kami. ---
**Author:** ![panto](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/f9ae1b/32.png) [@panto](https://www.ruby-forum.com/u/panto)\ **Post date:** [April 25, 2014, 4:04am UTC](https://www.ruby-forum.com/t/reference-clock-power-level-for-ettus-n210/240617/9 "2014-04-25T04:04:23Z")
Thank you all for the precious suggestions. Antonio