Hi I would bet that the spur moving is an indicator of either the 25 MHz transmitter carrier or modulator drifting in frequency. My guess is that the Maser does not drift :)
Bob > On Jan 20, 2017, at 12:22 PM, Anders Wallin <anders.e.e.wal...@gmail.com> > wrote: > > I made some progress with this issue today. > It turns I was using a 75Ohm cable at some point (doh!) which caused a > 'forest' of spurs far out. Possibly our other maser has a faulty/cut cable > which behaves similarly. > The final fix was to turn off our 25 MHz radio time-code transmitter which > was causing the strong close-in spur at around 1.5 Hz. It uses a modified > DCF77 code where it transmits full power AM-modulated 25MHz carrier for 0, > 100ms or 200ms at the start of each second. > > Here are PN plots of the 5MHz maser signal, same signal through 75ohm > reflective cable to the doubler, and through a 50ohm cable > to the doubler which solves the far-out spurs, and finally turning off the > radio transmitter. The result is now close to the +6dBc/Hz expected for a > doubler. > https://goo.gl/photos/qKKvg3SfE1XKxtq17 > as a time-series of residual phase the switchoff of the time-code > transmitter looks like so: > https://goo.gl/photos/jNVJK2kj1kGUkSVd9 > > Finally I tried it with the transmitter on, but reduced coupling into the > lab by disconnecting a few monitoring-cables. Strangely this shifts the > spur even closer in (close to 1Hz now) and reduces the amplitude as expected > https://goo.gl/photos/jG6rxfuC8R2QKchM6 > > What makes frequency doublers especially sensitive to this kind of > interference? The 25MHz carrier is phase-locked to better than 1e-12 to our > masers, so there can't reasonably be a 1-1.5Hz offset in the carrier > frequency. What is the interaction? (5th harmonic of 5Mhz mixes with 25MHz?) > > Anders > > > On Fri, Jan 20, 2017 at 11:06 AM, Anders Wallin <anders.e.e.wal...@gmail.com >> wrote: > >> Thanks for all the comments so far. >> I will try the doubler with another quieter source, and try removing >> various potential noise-sources and exchanging cables... >> >> I have now uploaded a few more images of the same data to the shared album >> linked in my earlier post. >> >> Anders >> >> On Thu, Jan 19, 2017 at 10:39 PM, Bill Byrom <t...@radio.sent.com> wrote: >> >>> I see spurs at 50 Hz and harmonics, which I assume are from the power >>> line at your location. This might be due to an oscillation in the power >>> supply regulator, leading to nonlinear regulator operation and >>> feedthrough of power line ripple. For example, low dropout regulators >>> can sometimes oscillate when an additional ceramic bypass capacitor is >>> added due to decreased phase margin in the feedback loop. It's also >>> possible that there is too much ripple before the regulator and you are >>> exceeding the dropout voltage, or that the regulator is going in and out >>> of an overcurrent condition. Many odd things may happen if the power >>> supply regular isn't working properly. >>> >>> >>> -- >>> >>> Bill Byrom N5BB >>> >>> >>> >>> >>> >>>> _________________________________________________ >>> >>>> time-nuts mailing list -- time-nuts@febo.com >>> >>>> To unsubscribe, go to >>> >>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> >>>> and follow the instructions there. >>> >>> >>> _______________________________________________ >>> time-nuts mailing list -- time-nuts@febo.com >>> To unsubscribe, go to https://www.febo.com/cgi-bin/m >>> ailman/listinfo/time-nuts >>> and follow the instructions there. >>> >> >> > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.