[time-nuts] ADEV query Timelab and TICC
Tom Van Baak
tvb at LeapSecond.com
Mon Mar 20 12:48:24 EDT 2017
This should not happen with the hp 5065A or 5061B frequency standards. I'm glad you worked around it by using a TAPR divider, but let's see if we can figure out the actual problem.
One thing to know is that the 1PPS output level from the 5061 and 5065 is *HUGE*, even up to 10 volts. If you send this to most counters it will blow the inputs or cause other undesirable side-effects, like the bouncing and spikes that you speak of. So always check your output and input signal levels and waveforms using a 'scope. Do this in-circuit, with all cables attached. Use attenuators and termination as appropriate for your counter's input specs. Set your DC trigger level to best match the actual waveform seen by the counter (not the waveform sent by the frequency standard).
Yes, the usual way you find out about this is that your ADEV measurements don't look right. The good news is that you can often tell within seconds that something is wrong. It's almost always a signal conditioning or trigger level issue, not a flaw in the instrument itself.
The TAPR dividers tend not to have "this problem" because they output at wimpy TTL/CMOS levels.
Older equipment can have powerful outputs. 10V into 50R is, what, 1/5th of an amp? Logarithmically, that puts a 5061A 1PPS closer to an automobile starter motor or heart defibrillator compared to modern logic gates.
----- Original Message -----
From: "timeok" <timeok at timeok.it>
To: <time-nuts at febo.com>
Sent: Monday, March 20, 2017 12:56 AM
Subject: Re: [time-nuts] ADEV query Timelab and TICC
> the similar problem I have verified using the HP5065A and HP5061B 1PPS output, the dividers are pratically unusable for ADEV measurements. The 5/10MHz output of the same instruments using the TAPR divider are ok, so these dividers have some spike noise problems. It can be seen even using other TIC as The HP53132A.
> Da "time-nuts" time-nuts-bounces at febo.com
> A "Discussion of precise time and frequency measurement" time-nuts at febo.com
> Data Sun, 19 Mar 2017 20:03:29 -0700
> Oggetto Re: [time-nuts] ADEV query Timelab and TICC
> > I have sent a couple of files to Tom. They were taken simultaneously from
> > an LTE Lite - one from the PPS and one from a PicDiv dividing the 10MHz to
> > 1Hz. The glitches were on the PPS trace, but not on the PicDiv trace, so
> > I'm fairly confident the TICC was working correctly.
> > Orin.
> Hi Orin,
> Thanks for the raw data. It's very nice (2 hours 16 minutes = 8219 points). Everything looks fine with the exception of 8 glitches. These are sometimes obvious jumps in phase, which cause massive spikes in frequency. Two plots attached.
> Almost every data point is within a few ns of each other. This is good. The standard deviation is a fraction of 1 ns. But once in a while there is a relatively massive phase jump. This is bad. Interestingly these 8 phase jumps all appear to be about 25 ns or a multiple of 25 ns in magnitude. The full list is (ns units):
> 25 * N ns is not random. So I think this is not a Windows problem, not a USB problem, not a TimeLab problem, not a TICC problem either.
> It makes me wonder if this is a LTE-Lite problem. If Said or Keith from Jackson Labs is around -- is there anything on the LTE-Lite board that's close to 20 or 40 or 80 MHz? At this point I kind of trust Orin's data and I kind of trust the TICC. So when I see monster 25 ns phase jumps it makes me think there's a problem with the GSPDO board itself.
> (Please realize that only on time-nuts may we can use the words "monster" and "25 ns" in the same sentence; the rest of the world has larger problems)
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