On Thu, 12 Jul 2007, Rick (W-A-one-R-K-T) wrote:


I have a so-called "modified sine wave" inverter that is connected to
200+
amp hours of deep discharge battery located in about the center of the
house in the basement. About a 30-foot length of #14 wire goes to an
outlet box in the shack, down on one end of the house, and provides
110VAC
(of a sort) when the power is off and I don't feel like hauling out the
generator. :-)

Trouble is, whenever I turn on the inverter it spews harmonics all up and
down the HF band and makes it difficult to impossible to hear weak
signals.

I realize that a pure sine wave inverter would mostly alleviate this but
that's not gonna happen any time soon... meanwhile is there a filter I
can
apply to the output of the inverter to round off the corners of the
modified sine wave (which is really nothing but a stairstep square wave)
and eliminate the worst of the harmonic noise?

How about picking up a line/power conditioner from ebay? Those tend to go
for reasonable money, and are meant to clean up dirty power lines. Should do
admirably cleaning up most of the square wave noise in one of these
inverters. Perhaps even an ordinary isolation transformer would cut a large
percentage of it, especially if you place a simple line filter on the
output. You could check this to some extent using any step down transformer
and looking at the output on an o-scope.