); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] Gents,
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 and 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 resolution. 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. TIA Ulrich Bangert Brooke, I hope you find my signature ok now? Ulrich Bangert www.ulrich-bangert.de Ortholzer Weg 1 27243 Gross Ippener Germany _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
