Hi Denton,
Denton wrote:
> I notice there is considerable rfi comming from the ups when it is active.
>
What do you mean by when it is active? There is more than one scheme for
UPS systems. Some have a charger and an inverter running all the time,
others have a very fast switching system and only run the inverter when
there is really a supplied AC power outage. In one of those "active"
could mean that the charger is on to maintain the battery and the
inverter is not. There may be more than one charging mode too.
> The ups is supposed to be emi/rfi filtered and has an isolation transformer
> on the ups output. Scoping the output of the ups indicates a so called clean
> ac sine wave. Testing of the ac line input and output of the usp indicates
> correct wiring.
>
What do you mean by "so called clean AC sine wave"? Inverters that do
generate good clean sine waves usually do so using some sort of switched
mode generation of the sine wave. Do you know the switching frequency,
can you see steps in the sine wave or some other artifact of the switch
mode operation, and if so does it correlate to the noise on the radio?
> Clamp on ferrite chokes on the ac output of the ups has little effect.
>
For the highest efficiency, the UPS may use a switched mode DC
supply/charger. Maybe the noise is generated by the "front end" (battery
charging part) of the UPS more than by the "back end" (inverter part).
Try ferrites on the AC input. Can you scope the input AC supply and see
if it is clean too?
> I would like to get rid of the rfi into the radio station. Rfi is most
> prevalent on 40 thru 20 meters..the other bands seem to be uneffected.
> Radio station is heavly grounded on its own ground rod system, not directly
> connected to the ups.
>
You could try some experiments to determine whether the noise is
conducted to the radio gear through the power lines, or radiated from
the power lines and picked up by the antenna. Maybe temporarily run the
radio directly from the AC line, or even better from a battery if the
radio can easily run on DC power, and connect various test loads to the
UPS with various length wires from the UPS to the load. How about a
medium sized resistive load (for the rating of the UPS) like a heater,
connected with as short cables as possible and nothing else hooked up to
the output of the UPS. Compare that to the same load connected through
your usual distribution wiring. The bands most effected may relate to a
length of AC power cable that radiates harmonics of the UPS switching
frequency more efficiently on those bands.
DE N6KB
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