[time-nuts] UPS for my time rack

Bob Camp kb8tq at n1k.org
Sat Oct 10 10:51:09 EDT 2015


All of the UPS vendors these days make a wide range of products. They range from 
low cost to mighty expensive. They also range a bit in terms of performance. Finding out
exactly what this or that model *does* do can be a major pain. The marketing guys apparently
don’t want you to figure out that the low cost gizmo does not have all the performance 
of the one that costs 5 times as much. 

First thing to avoid - the pure square wave output versions. These may or may not
generate RFI in this or that UHF band. They will take out big chunks of HF and mess up 10 MHz
distribution. I suspect that the filters on some are better than the filters on others. The bigger issue
is that they do not play nice with modern power factor corrected power supplies. These supplies 
seem to expect a sine wave and a (possibly ringing) square wave may get them confused.

Next thing to avoid - The stepped square wave / modified square wave versions. Theses aren’t 
quite as bad as the centuries old square wave units. It’s more likely you will find these than a 
pure square. They still have the same issues on RFI. They may or may not antagonize a PFC 
supply to the same extent. 

The target is a “pure sine wave” output. That keeps a PFC supply happy. As with any verbal spec, 
“pure” likely has a few qualifiers on it. It’s not guaranteed to take out the RFI. It at least will reduce 
the spikes on your 1 pps lines. If you look at the output on a ’scope the waveform at least *looks* like
a sine wave. 

All of these gizmos run a switcher in the “few hundred KHz” range to generate the output. They run 
a similar switcher to charge the battery. None of them are compatible with an indoor antenna in the same
room trying to listen to MF. None of the ones I have tried are nasty enough to bother GPS, either indoor or
outdoor. Put another way, I’ve had more trouble from LED lights than from sine wave UPS’s. 

Cyber Power (via Amazon) seems to make some pretty good stuff at a price point a bit below APC. As
with everybody else, it’s a pain to figure out what’s what. Are you after a “big” rack mount unit (as in $500
and up) or something smaller?


> On Oct 10, 2015, at 9:20 AM, Chris Waldrup <kd4pbj at gmail.com> wrote:
> Hi,
> I have decided I'd like to get a UPS to put on the rack containing my Thunderbolt, the laptop that runs Lady Heather, and frequency counter. 
> Has anyone had bad experience noise wise with the APC brand units like are available on Amazon and at Staples? I'd like to get one that doesn't generate lots of RFI. Thank you. 
> Chris
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