[RFI] UPS Radiated Interference

Bob K0NR (email list) list at k0nr.com
Sat Jan 26 23:25:59 EST 2008

David K1TTT recommended trying UPS units from either APC or TrippLite.
I bought a TrippLite (Model BC 350) from tigerdirect.com

The TrippLite is much, much quieter with respect to RFI compared to the
UPS it replaces.
I have 3 UPSs in the house, so I am going to replace all of them with
the TrippLite units.

Thanks for the help, David.

73, Bob K0NR

wa4tuk wrote:
> The units I salvaged used the transformer to trickle charge the
> battery and then the transformer was driven by an inverter from the 12
> volt battery to made pseudo sine waves when needed but not all the
> time. The trickle charge function was RF quiet. The UPS inverter was
> switched on quickly by a relay when the AC line fails so there is a
> short time with no AC present that a good PC power supply could
> withstand. So these were more accurately "standby" power supplies
> because they allow a brief interruption.
> I guess there is a savings in copper and shipping costs to use a
> switcher for the battery charge.
> You might shop by favoring the heavier units and at stores that allow
> no hassle returns. I'm wondering now if almost all UPS manufacturers
> have gone to switching types due to energy efficiency requirements.
> If you do locate a quiet model please let me know and I'm sure the
> list would be interested.
> Pat
> wa4tuk
> Bob K0NR (email list) wrote:
>> Pat,
>> Yes, I unplugged the equipment that the UPS is powering, so it really is
>> the UPS.
>> I said "switching regulator" but it might be more accurate to say
>> "switching inverter" (DC battery to 120 VAC).
>> These are el-cheapo off brand UPSs.
>> Bob
>> wa4tuk wrote:
>>> They certainly could be switching supplies; however, the ones I've
>>> disassembled after failing have had iron core laminated transformers.
>>> These were APC and Tripp-Lite brands. In fact, I've contemplated using
>>> them in reverse as filament transformers. It could be that newer
>>> models have all moved to switching supplies.
>>> When these UPS's are asked to provide emergency power they do make an
>>> strong RF buzzing howl.
>>> I would guess that you pulled the PC's and monitors AC cord to be sure
>>> it wasn't the PC/monitor that was making the noise? Many newer PC's
>>> have a small switching supply that is always on to support
>>> "wake-on-lan" and other features. And the monitors just go to a
>>> standby low power mode. That's part of the reason my PC's are fed from
>>> a switched outlet strip.
>>> Pat
>>> wa4tuk
>>> Bob K0NR (email list) wrote:
>>>> I tracked down some RFI problems on the 2M band to several small
>>>> Interruptible Power Supplies in my house. These are the
>>>> half-a-shoe-box
>>>> size units intended for use with PCs. I assume the switching regulator
>>>> inside is the source of the noise.
>>>> I am thinking my best strategy is to replace them with higher quality
>>>> units (rather than try to suppress the noise).
>>>> Any suggestions on models of UPSs that don't radiate?
>>>> Any other ideas?
>>>> Bob K0NR
>>>> Bob Witte K0NR
>>>> bob at k0nr.com
>>>> Technical Coordinator
>>>> ARRL Colorado Section
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