Last update: 10-August-2003

CRO Test-results:

ZDF(TV)-Reference vs. GPS. (HW rev. 1)
	The example shows the typical behavior of TV-PLL synchronized units of this design.(like designs by DK2DB and DK6RX ).
	Course of the reference hardware at the 27th of August 2001. Starting 5 seconds after switch on, until almost 2 hours behind. The shown precision is a calculated average and can not directly be used ! For an user of such HW only the slope of the current graph is important. Only that slope is an image of the current precision.
	The worst case here is better than 1*10exp-8. This is a rather good value for a regular counter. The average about 4 hours shows a precision of about -4*10exp-11. The problem however is, that the usable precision for a counter varies between -1*10exp-8 and +1*10exp-8.
Rubidium vs. GPS
	The reference signal was taken by GPS and the oscillator under test was a 10 MHz Rubidium Standard Frequency Generator by Rohde&Schwarz.
	The top graph shows the course of short-term stability of the Rubidium Standard  and the calculated Accuracy (green line) over 12 hours.  The mid graph shows the same  result, however the source is an IIR filter which causes a much more smooth graph.  The bottom graph shows the noise of the GPS reference and the Rb-Standard from second to second. The resolution is around 10ns.
3-SAT Doppler
	The screen shot below explains why a TV-Satellite based reference can not be a reliable reference source.
	The picture shows the precision of the 3SAT TV-Satellite within 24 hours. Due to the motion of the satellite, the usable precision changes dramatically per day. 2 times a day the precision is excellent (gradient is zero). But 2 times a day the precision is rather lousy. Between that both extreme values, any precision can be guessed. The Doppler effect is responsible for that behavior.
GPS-Receiver
	Differences between TIM-LP and MS1
	Both GPS-Receiver can be recommended for the CRO as a 1PPS reference source. However, the MS1 is better. The picture on the left shows the differences. The MS1 has a 1PPS jitter of +/- 30 ns, the TIM-LP has jitter of +/- 40 ns. Also it seems that the 1PPS signal from the TIM-LP is more restless.
	Important information about TIM (not TIM_LP!)
	The current TIM firmware (E010) has a bug. The bug causes that the 1PPS pulse jumps any (around) 35 minutes for a certain amount of time. It can be seen in the Online-Analysis SW as a recurrent disturbance (blue marker) after the mentioned time interval. u-Blox knows the bug and they promised to fix it in the next SW release. From the jitter point of view the TIM seems to be a bit better than the TIM-LP .