Moin, On Sun, 27 Jun 2010 02:24:31 -0700 Said Jackson <saidj...@aol.com> wrote:
> The 4002 expects a tight phase lock on the two inputs to properly stay > locked, Why does the ADF4002 need that? Or do you mean by "locked" that the locked output of the ADF4002 does reflect the actual locked state? If you mean that, i dont think i will use that at oput. Maybe as a debugging help, but not for the control loop itself. As for the design, i wanted to rely on the ADF4002 haveing a linear phase difference response within [-2Pi,2Pi] and integrate over the phase error to average out the jitter introduced by GPS. > and your adc/dac will likely introduce too much phase lag and > cause oscillation. In fact when using the Analog Devices PLL simulator > one has to closely follow the component values of the loop filter that > the software suggests otherwise the system won't be stable, unless you do > a lot of manual math. The 4002 works well with loop bandwidths of 30 Hz > or more. The exact control of the loop parameters are exactly the reason why i want to use a uC implementing the control loop. Implementing such low frequency control loops is a lot easier in software (or rather digitally) than it is doing with analog electronics. And yes, i'm quite aware that i'd have to tweak the loop parameter for stability. But i dont expect this to be difficult as long as the analog part is operated in its linear range. Unless of course, there is something in the electronics i have not taken into account. Which is why i'm asking here for advice :-) > For a GPSDO you are looking for loop bandwidths of 0.001Hz or less, a > totally different world. Even if you use the 10 Mhz output rather than > the 1 pps. This is because your Isotemp Ocxo will be much more stable > than the gps for short time intervals, say 0.1s to 500 s Yes, i'm thinking about a 1/f in the range of 100s to several 1000s. > What would be easier to try is to replace the gps internal Tcxo with > an external ocxo, but you have to generate the frequency the gps is > using, such as 26 MHZ and do some soldering on the gps itself. Yes, that would be an idea. But it's not that easy. I dont know how the control loop in the LEA-6 works and whether they are actively changing the TCXO frequency. If they are, i would need to provide a VCO that is stabilized, either in form of an seperate OCXO or by locking/syncinc the VCO to my 10MHz OCXO. I have one open LEA4-S infront of me. That has crystal mounted marked with R4130 and that looks from the configuration (two of the 4 pads on GND, two connected to other components) that it is a simple quartz without any voltage control. The Atmel uC (probably a SAM7 OEM variant) has only one small crystal connected to it that looks like a 32kHz quartz. No other frequency source is on the uC side of the module. Although the LEA4 is two generations older than the LEA6, i expect it to be at least similar by design. > It would be very interesting to see just how good the uBlox lea-6t can > work with an ultra stable frequency source rather than a $5 tcxo.. Yes. But then i'd have to build two devices, one that uses a stock LEA6-T and one that uses a modified LEA6-T and measure both to have an indication how much improvement this brings :-) Attila Kinali -- If you want to walk fast, walk alone. If you want to walk far, walk together. -- African proverb _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.