[Boatanchors] interference

Thu, 28 Aug 2003 11:02:11 -0400

I recently found a source of severe HF interference at GaTech in a UPS 
(Uninterruptible Power Supply) that was being used to power all the 
Ethernet network hubs in our building.  The interference signal was 
using all the network cabling in the building as a huge antenna, and 
essentially eliminated any HF reception (including AM broadcast) inside 
the building.  Strangely, it was not the switching output supply that 
caused the noise, but rather a noisy AC supply / battery charging 
circuit.  If the UPS was unplugged so that the switcher supplied all 
the AC power from the battery, the noise went away!

Bob
WB4TGG

On Wednesday, Aug 27, 2003, at 23:47 US/Eastern, WBob wrote:

> Makes some sense..If it ran at 50kHz and had odd harmonics, like a 
> nice square pulse. then 100kHz spaced stuff makes sense.
>
> WBob
>
> [email protected] wrote:
>
>> One thing to check is any switching power supply. Although some 
>> operate in the 40 KHz region, during a recent analysis of several 
>> modes, I found the strongest harmonic (on one unit I had) right on 
>> 7.040 MHz. Yep, I was trying to use it to power my QRP 
>> rig.......RIGHT on the CW calling frequency! Interesting to watch 
>> these harmonics on a spectrum analyzer. Especially during power on 
>> and off. Talk about a sweep generator......
>> Some are MUCH worse than others.
>> Regards,
>> ron
>> N4UE
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>
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> ** List Administrator - Duane Fischer, W8DBF/W9WZE **   ** For 
> Assistance: [email protected] **         $$ For vintage radio info, 
> see the HCI web site $$      http://www.w9wze.org