On 12/09/2014 07:32 PM, Nemanja Savic wrote:
is there any way to synchronize those two clocks sources?
Not on a USRP1.
On N200, there's support for "timed commands", which allows both
synthesizers to be locked to the same phase when they're re-tuned, but
that'll
leave you with a 0/180deg ambiguity, because the *mixer* used on the
WBX uses a 2XLO scheme, and the LO phase splitter can't be forced into
a specific state on tuning.
Synthesized LOs have this inherent property. Even when two synthesizers
share a common reference, it's unpredictable what their phase will be
when they lock to the LO. More so for so-called fractional-N
synthesizers, which are what's used in nearly everything these days. In
the case of
the WBX and SBX, they use a synthesizer from ADI (ADF4351) that has a
fairly-rare "phase resynch" feature which allows the chip to bring the
resulting LO into a particular phase relative to the reference clock,
using a hardware synchronization signal. That signal, and the FPGA code to
make it work, is only available in the N2xx and X3xx family. The
USRP1 FPGA codebase has been utterly-frozen for many years, and there's
*zero* room to do anything fancy, without leaving stuff out.
The usual way around this is to use a calibration signal that is common
to both receivers, and use that to calibrate-out the "per run" phase
difference.
On Tue, Dec 9, 2014 at 4:51 PM, Marcus D. Leech <mle...@ripnet.com
<mailto:mle...@ripnet.com>> wrote:
On 12/09/2014 04:42 AM, Nemanja Savic wrote:
Shouldn't relative phase be constant and 90 degrees for example
if transmitted wave had circular polarization?
The samples will be time-aligned, but those samples will have been
derived from two independent analog downconversion
chains, which means that the synthesized LO will have a
different relative phase (between the two sides) every time.
On Tue, Dec 9, 2014 at 10:38 AM, Nemanja Savic
<vlasi...@gmail.com <mailto:vlasi...@gmail.com>> wrote:
Yes, the platform is USRP1. What is relative phase in this
case if they are alligned in time?
On Mon, Dec 8, 2014 at 4:19 PM, <mle...@ripnet.com
<mailto:mle...@ripnet.com>> wrote:
You haven't stated which USRP motherboard platform, but I
assume you're talking about the USRP1, given the 4RX
image. Yes, the samples
will be aligned in time, but the relative phase will be
random every time you re-tune or start a new session.
On 2014-12-08 06:03, Nemanja Savic wrote:
Hi all guys,
I am about to make a receiver with two WBX
daughterboards. I want to receive simultaneusly with
horizontal and vertical antenna. For this purpose I want
to use 4RX FPGA image. My question signals obtained in
this way, from two daughterboards, alligned in time?
Many thanks,
--
Nemanja Savić
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--
Nemanja Savić
--
Nemanja Savić
--
Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org
--
Nemanja Savić
--
Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org
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