[RFI] APC BR1500 UPS RFI on 3.5 MHz

Michael Tope W4EF at dellroy.com
Sun Apr 10 16:47:41 EDT 2005

----- Original Message ----- 
From: "Stephanie WX3K" <wx3k at ptd.net>

> Greetings all,
> I just bought a APC Back UPS Model BR1500 about 2 months ago. I realized
> recently that it is generating hash on the lower portion of 80 meters
> that gives me a S9+ noise level. I use coax in the shack to all my
> antennas. The antenna is located about 60 feet away from the shack. Has
> anyone else experienced inverter hash from their UPS ??? Did you resolve
> the problem ? Did ferrites on the line cords help ?
> -- 
> Stephanie WX3K
> wx3k at arrl.net


I had very strong spurs on 160 meters (S9 +20 spaced ~15 KHz) from my
Belkin 1400VA unit. I didn't put 2 and 2 together until I had it on the 
in the garage a few months ago to replace the batteries. With the cover
off, it totally wiped out my AM radio reception in the garage. I wrapped
the line cord and the load cord (I plug a single output strip into the UPS
and then plug all the various loads into that strip) each around an Amidon
FT-240-77 (Fair-Rite products 5977003801) and that knocked down
the spurs so that they are close to my noise floor. I would recommend
that you use a #31 material toroid if you can find it (Fair-Rite products
5931003801) as it has good suppression over a much wider bandwidth
as compared to #77 material. These are 2.4" O.D. toroids which have
a big enough hole in them that you can make multiple passes through
the hole with a standard IEC power cord (I was able to get 9 to 10 turns
on each toroid). Keep the toroids close the UPS chassis so that the
cords will be less likely to radiate. If the UPS is conducting common-mode
noise through the power cords as was mine, this method should put a
big dent in it.

73 de Mike, W4EF................................ 

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