[USRP-users] Master Clock Supression

Andy Walls andy at silverblocksystems.net
Fri Jul 17 16:04:29 EDT 2015


On Fri, 2015-07-17 at 12:00 -0400, usrp-users-request at lists.ettus.com
wrote:

> Message: 26
> Date: Fri, 17 Jul 2015 17:19:14 +0200
> From: Marcus M?ller <marcus.mueller at ettus.com>
> To: usrp-users at lists.ettus.com
> Subject: Re: [USRP-users] Master Clock Supression
> Message-ID: <55A91CF2.10007 at ettus.com>
> Content-Type: text/plain; charset="windows-1252"; Format="flowed"
> 
> Shielding/separation-wise, the X310 should be pretty much superior in 
> every aspect -- not only is the ADC, DAC, mixer, amplifier and LO 
> synthesizers in one package on the B2x0 (the AD9361); the X310 is 
> modular in the sense that the MCR doesn't even appear to the 
> daugtherboards, necessarily; it's an FPGA-only clock, generated by
> the 
> clock distribution IC on the mainboard, and the UBX, especially to 
> suppress strong interferers, has a metal can (which is unique among
> our 
> RF hardware, so far). Under that metal can, there's a lot of
> partitions, 
> which align with the different jobs and frequency ranges on the
> board, 
> compare the schematic [1].
> 
> So since you're seeing 200MHz-harmonics, these might either
> spuriously 
> get into the antenna ports, or for some reason, at multiples of
> 200MHz 
> LO leakage is worse (I don't expect that). Have you tried using
> offset 
> tuning [2] to reduce these spurs?

I have an X310 with a WBX-120.  For my work between 156-162 MHz, I too
notice the 200 MHz clock being emitted during Tx bench tests with a
spectrum analyzer.

The spur is independent of Tx power level and offset tuning doesn't make
a difference.

(I suppose what I haven't done is move the spectrum analyzer across the
room to ensure I'm not getting some sort of near field coupling.)

Filters at VHF with sharp-ish cutoffs can get bulky or expensive.  I'd
love to know of a way to easily supress the 200 MHz X310 clock
fundamental.  Setting the master clock to something like 150 MHz just
makes my filtering constraints worse.

Regards,
Andy


> Best regards,
> Marcus
> 
> 
> [1] http://files.ettus.com/schematics/ubx/ubx.pdf
> [2]
> http://files.ettus.com/manual/page_general.html#general_tuning_process
> 






More information about the USRP-users mailing list