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

[Alan Kamrowski II]

Hi Bob,

I've got one of these:

MCP9701A-E/TO-ND:
http://www.digikey.com/product-search/en?x=0&y=0&lang=en&site=us&KeyWords=MC
P9701A-E%2FTO-ND

Mounted to the connector side of the LPRO.  I made a small aluminum bracket
that fits under the hex head connector screws and clamps the TO92 to the
LPRO case.  It isn't at the physics end or taking the temperature of the
base plate, but I am hoping that it will do.

It outputs a voltage 400 mV = 0 deg C + 19.5 mV per deg C.  I've got it
feeding into an ADC channel on an AVR with a precision 2.5V reference.  I've
not calibrated it, but my ir temp sensor agrees pretty close to it, but
calibration to a specific temp really isn't my goal, keeping the LRPO at the
same temperature as much as possible is.

Thanks,

Alan

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Bob Camp
Sent: Thursday, September 12, 2013 8:01 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

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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