[time-nuts] (no subject)
kirbybq at bellsouth.net
Sat Jul 7 11:15:30 EDT 2007
You need another independent reference oscillator for the 3325 and run
the test again - that should make sure its not a synchronization
It could be at that low of a frequency change, they are swallowing a
pulse and it makes a jump....
Ulrich Bangert wrote:
> ); SAEximRunCond expanded to false
> Errors-To: time-nuts-bounces+kirbybq=bellsouth.net+kirbybq=bellsouth.net at febo.com
> perhaps you know that Bruce and I are working on an linear phase
> comparator similar to the K34-5991A from HP (but with some features of
> today) which should enable us to characterize even "better" oscillators
> at an very small price. The first expriments (running since some weeks)
> are very encouraging but now an problem has arised that I would like to
> hear your comments to:
> For linearity tests of the circuit I need two signals that are
> a) low phase noise
> b) have an very small stable frequency offset, say 0.001 to 0.005 Hz.
> The two signals that I use are
> a) 10 MHz coming from my well hung FTS-1200 + frequency doubler
> b) The SQUARE output of my HP3325A set in amplitude and dc offset so
> that effectively an cmos like digital signal is generated. The HP3325
> uses the FTS-1200 as external reference. I am using this arrangement
> because of the ease of offset generation as well because the linear
> phase comparator currently features an well designed sine to ttl
> converter only on one of its input channels, so the second channel needs
> to be fed digital.
> The slow beat frequency slowly shifts the phase delay between the phase
> comparator input clocks and one should get an linear output of the lpc
> over time. Looked at the big scale (200 ns measurement range) the
> voltage recorded at the lpc's output looks indeed picture-perfect.
> If however looked at an scale of an few ns it becomes obvious that there
> is an regular sudden jump in phase of abt. 320 ps (always same
> direction) every 60 seconds or so. Bruce and I have tried to remove
> zillions of possible sources for that without any result. As an last
> resort I made an measurment that recorded the phase comparator's output
> as well as an direct time interval measurement between the positive
> slopes of the input clocks and much to my surprise the jump was already
> to be seen there although buried in a bit more noise due to 20 ps tic
> I am almost sure the FTS-1200 can NOT be the source of these jumps
> because it is at the same time the LO of my GPSDO system. If it were to
> produce regular phase jumps (even that small) they would accumulate to
> an value that would result in an noticeable reaction of the closed loop.
> Therefore the qustion: Has anyone of you an theoretical knowledge about
> the HP3325 that would explain this behaviour or has anyone of you made
> similar findings? In the above example the frequency had been set to
> 10.000000005 Mhz, square output, 5V amplitude, 2.5V dc offset which
> gives an 0 to 5 V when terminated into 50 Ohms. Can it be that the
> effect is due to the sqare output? I made some tests whith seeting the
> phase of the output signal which led to no noticable changes so there
> could be an signifant difference of signal phase behavoiur between sine
> and square generstion.
> Ulrich Bangert
> Brooke, I hope you find my signature ok now?
> Ulrich Bangert
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> 27243 Gross Ippener
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