Thanks for the good advice Ken....I am also forwarding this to the other
local ham club members...
Ok good advicer...sine wave from the ups looks very clean...very few
jaggies...definitely a sine rather than a stepped wave....when the ups is
inactive, the 120 vac in this qth looks very good. I will re-scope the ac
output again when I get all my work done.
When the ups is inactive....normal 120 vac operation...there is no rfi from
the unit. When I used to kill the circut breaker to the ac line feeding the
ups, then the rfi shows up...
However, I did a few things that have gotten it down to a much less rfi
level.
I have a long wire monitoring antenna, with the feedpoint just on the other
side of the wall of the basement where the ups resides, when I pulled down
that particular hf antenna, a lot of the rfi went away. It dropped to a
further level when I put ferrite clamp chokes on the dc lines from the
battery pack to the ups, and re-installed an isobar on the ac line from the
ups that feeds the radio station. Some other lower end ups manufacteurers
state not to install additional filtering after the output of a filtered
ups, but the literature I downloaded for my particular ups says nothing in
that regards. To my thinking, the more filtering, the better.
I still have a tad of rfi from the ups on 40 meters, but it is not
interfering with weak signal work on that band near as much as it was...by a
long shot.
The radio station currently resides in the upstairs office that is just
above the basement room where the ups is residing..since we are doing some
remodeling, the radio station and our computer stations will be moved to
another room, doubling the distance to the ups....a bit more grounding work
and isolation, and I think it the rfi will no longer be an item.
We are having a lot of variable weather this fall...two snow storms already
and can get some real nasty wind and rain storms going thru this
area....already have had at least 3 times the normal ac power failed for a
short period of time and the radio and computer stations didn't even
blink...so the ups system is doing its job.
Lead acid gas absorption mat batteries are sure expensive these days! Too
much demand for lead worldwide is my understanding.
----- Original Message -----
From: "Ken Brown" <ken.d.brown@hawaiiantel.net>
To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
Sent: Wednesday, December 05, 2007 10:30 AM
Subject: Re: [TenTec] Cyberpower 3000 rif
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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