On 05/22/2018 08:42 AM, Teemu Veijalainen via USRP-users wrote:
Hi,
And thx for the reply.
The manual (http://files.ettus.com/manual/page_gpsdo_b2x0.html) states
that the GPSDO is detected automatically so I think I don’t have to
configure it:
* /“By default, if a GPSDO is detected at startup, the USRP will be
configured to use it as a frequency and time reference/
Also, when probing the USRP it returns:
* “Detecting internal GPSDO.... Found an internal GPSDO: GPSTCXO ,
Firmware Rev 0.929a”.
So looks like it is detected.
The manual also states that the GPSDO is initialized to GPS time :
* /“The internal VITA timestamp will be initialized to the GPS time,
and the internal oscillator will be phase-locked to the 10MHz
GPSDO reference. If the GPSDO is not locked to satellites, the
VITA time will not be initialized.”///
I’m not using GPS antenna, and I assumed that since the GPSDO provides
GPS unlocked refence of 75ppb and GPS locked reference of <1ppb then I
don’t need GPS to initialize. However, the above sentence from the
manual doesn’t state clearly that the GPSDO can be used without
initialed by GPS, could it be e.g. that GPS is needed to initialize
the GPSDO and then GPS signal can be lost to get the unlocked
accuracy? Or could there be still some other reason?
Br, Teemu
My suspicion is that a GPSDO that has "never seen the sky" will not be
as good as one that has, and is operating in holdover mode.
The stated 1.7kHz in 3.75GHz, is about 400PPB, which is what I would
expect from an undisciplined TCXO.
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