How to syncronize 2 XCVR2450 daughterbords


#1

Hey all,

I have a setup that transmits using one USRP+XCVR2450 set and receives
using another USRP+XCVR2450 set.The two are separated just 1meter away
in my experiment. I am looking at small doppler signals around the
carrier. But there is a lot of phase noise in the data that i receive,
which masks these doppler signals.

I want to make the two XCVR2450 daughterboards use the same oscillator
in an attempt to decrease the phase noise.
So, could you explain me how to syncronize these boards to use same
oscillator and where can i get detailed information about the steps to
make it.
Also, is there some other way to decrease phase noise between
daughterboards?

thanks!

Bruhtesfa


#2

So, could you explain me how to syncronize these boards to use same
oscillator and where can i get detailed information about the steps to
make it.
Also, is there some other way to decrease phase noise between
daughterboards?

thanks!

Bruhtesfa

The instructions for linking the clocks are here:
http://www.gnuradio.org/trac/wiki/USRPClockingNotes

Jason


#3

Jason U. wrote:

So, could you explain me how to syncronize these boards to use same
oscillator and where can i get detailed information about the steps to
make it.
Also, is there some other way to decrease phase noise between
daughterboards?

thanks!

Bruhtesfa

The instructions for linking the clocks are here:
http://www.gnuradio.org/trac/wiki/USRPClockingNotes

Jason

Thanks!

But I am confused with one thing.

I have read that the VCO on daugherbords uses PLL frequency synthesizer
by using the USRP clock as a reference. If I syncronize the two USRPs(to
work as a master and slave), will the Daughterboards,XCVR2450 operating
on them become frequency and phase synchronized?

Also on the USRP clocking notes, a step is desribed to “disable the
daughterboard clock and enable the motherboard clock”. So, which is the
reference for the PLL frequency synthesizer by default, the
daughterboard clock or the motherboard clock?

Thanks!


#4

Matt E. wrote:

Bruhtesfa E. wrote:


I have read that the VCO on daugherbords uses PLL frequency synthesizer
by using the USRP clock as a reference. If I syncronize the two USRPs(to
work as a master and slave), will the Daughterboards,XCVR2450 operating
on them become frequency and phase synchronized?

YES. That is the whole point.

Each XCVR2450 has its own local oscillator which is locked to the master
clock on the USRP motherboard. You can make both USRPs share the same
master clock by following the directions above. You CANNOT make both
XCVRs use the same local oscillator, you can only make them lock their
own LOs to the master clock. However, both will then produce
phase-locked, frequency-locked output.

Also on the USRP clocking notes, a step is desribed to “disable the
daughterboard clock and enable the motherboard clock”. So, which is the
reference for the PLL frequency synthesizer by default, the
daughterboard clock or the motherboard clock?

That does not apply to you. That is for old RFX boards, not XCVR2450
boards.

Matt

Thanks Matt!
But,could I ask you 2 more questions please!

1.Where can i get the specification,block diagrams or schematics(PCB)
for this XCVR2450?
2.Currently I am using Gnuradio 3.0, but i want to update to the upto
date version. So, does this board has compatibility(works without
problem) with the newest versions of gnu radio?

Bruhtesfa


#5

Bruhtesfa E. wrote:


I have read that the VCO on daugherbords uses PLL frequency synthesizer
by using the USRP clock as a reference. If I syncronize the two USRPs(to
work as a master and slave), will the Daughterboards,XCVR2450 operating
on them become frequency and phase synchronized?

YES. That is the whole point.

Each XCVR2450 has its own local oscillator which is locked to the master
clock on the USRP motherboard. You can make both USRPs share the same
master clock by following the directions above. You CANNOT make both
XCVRs use the same local oscillator, you can only make them lock their
own LOs to the master clock. However, both will then produce
phase-locked, frequency-locked output.

Also on the USRP clocking notes, a step is desribed to “disable the
daughterboard clock and enable the motherboard clock”. So, which is the
reference for the PLL frequency synthesizer by default, the
daughterboard clock or the motherboard clock?

That does not apply to you. That is for old RFX boards, not XCVR2450
boards.

Matt