[time-nuts] RFTGm-II-Rb - can you gps discipline it without the XO module?

[Bob Camp]

Hi

Be very careful of using the same sensor to control your loop and to determine how well the device is holding temperature. It's amazingly easy to fool yourself by a couple of orders of magnitude…. The test is always to have a couple of other sensors located around the device and see what happens to them. 

That said, the real fun is to see how much thermal gain the loop has. If the outside temperature changes 100 C how much does your LPRO change? A 1 C change would be a thermal gain of 100X. Practical single stage controllers can get you into the 300 to 500 range. If your room ambient changes by 4C, the device should change by 0.04 C with a thermal gain of 100. 

Bob

On Sep 12, 2013, at 8:52 PM, "Alan Kamrowski II" <alank2 at earthlink.net> wrote:

> Hi Guido,
> 
> A couple more questions about the RFTG if you have a moment:
> 
> What are you default values for Avg Sample, Time Corr Schedule, and Freq Corr Schedule.  Mine are 5, 15, 1440...
> 
> Also with yours up and running how often does it make adjustments?  Mine has been running for 82 hours and has made no time adjustments and the three frequency adjustments (every 24 hours) are for "0.0000e+000".  It would seem that it is pretty happy with where it is as all of my previous times were loaded with both time and frequency adjustments in an attempt to get itself set properly.  Perhaps it finally did.
> 
> I've attached a temperature sensor to the LPRO inside and am using a PID loop on an AVR to vary a fan rpm to keep the LPRO at a consistent temp.  It seems to be keeping it at +/- 0.2 deg C and I've not bothered to try to tune the PID at all yet.
> 
> Thanks,
> 
> Alan
> 
> 
> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On Behalf Of Guido Küppers
> Sent: Friday, August 23, 2013 1:25 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] RFTGm-II-Rb - can you gps discipline it without the XO module?
> 
> Hi Alan,
> I haven't seen this behaviour yet, but then I have RFTG shut off for a couple of months since.
> 7168 is dividible by 7 and the result is 1024. You know the gps week wraps over from 1023 (0x3ff) to 0.
> Perhaps what you see is the consequence of some software workaround of this problem, in other words the RFTG thinks a gps week rollover must have happened and tries to correct the date.
> Have fun
> Guido
> 
> Von Samsung Mobile gesendet
> 
> Alan Kamrowski II <alank2 at earthlink.net> hat geschrieben:
> 
> Hi Guido,
> 
> Do you have any idea why the unit interprets the date 7168 (0x1c00) days into the future?  If I send it today's date in the correct Motorola format, this is how many days it adds to it.  If I change the date to try another, it does the same thing.  Any idea why?  I can correct for it by subtracting 0x1c00 days before sending it, this just seems very odd.
> 
> Thanks,
> 
> Alan
> 
> 
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