[ntp:questions] Re: Comparing offset of multiple refclock/servers

David L. Mills mills at udel.edu
Tue Aug 23 03:08:24 UTC 2005


It's not that simple. The original power line RFI I have been hearing 
for fifteen years is in fact a 60-kHz line source modulated by a 60-Hz 
square wave. I can hear it on a longwave receiver and verify with 
oscilliscope at the synchronous detector in the radio. The stuff in our 
machine room is wideband hash, allegedly due the UPSes, but it is 
possible that some other switching regulator is causing the blast. 
Doesn't matter either way; the WWVB receivers don't work.

I gave one of our WWVB receivers to the campus IT and suggested they 
bring it up to see if they have the same problem as the department 
machine room. No reply yet.

My three APC 2200 VA UPSes are reasonably good citizens, even though 
they are FCC Class A devices. No trouble with the radios if the mains 
have juice, but they do generate a wideband frying noise when on 
battery. I haven't tried to find the inverter frequency. Whatever the 
fundamental or harmonics, it doesn't affect any ham bands I occasionally 
haunt when doing health and wellfare during hurricane season.

What specs I can find say nothing about the inverter frequency.


Hal Murray wrote:
>>We have a 6KVA Masterguard UPS in our Server room and no DCF77 reception 
>>problems. Before that we used to have a smaller Masterguard UPS which 
>>also was not problematic, so I guess they work for us DCF77 geeks.
> Maybe somebody should start a web page listing UPSs that do/don't
> interfere with low frequency time signals.
> It would be even better if somebody could measure the switching
> frequency or find it in the specs.

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