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?

Thanks...

"Rick " ) writes:
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?

Thanks...

Look in old ARRL Handbooks, or even their old Mobile Handbook.

A lot of the things about alternator noise would seem to apply
to such inverters, and even switching supplies. But it seems like
such coverage is much smaller nowadays than thirty or so years ago.

Figure out whether the signal is radiating from the chassis, or from
the output wire. If it's the former, it needs better shielding. If
it's the latter, add feedthrough capacitors in a box that shields
the output, and maybe put an LC circuit in series with the output
line, and tune it for a null. The primary of the inverter may also
be a source of noise, you need to figure that out first.

Michael VE2BVW

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?

Thanks...

Shield the inverter and the battery together,
put an ac filter made for computers on the output of the inverter were it exits
the shielded enclosure, and ground the shielded enclosure to earth. You should
see a big difference in noise...

Bob N9LVU

On Thu, 12 Jul 2007 19:37:21 +0000, Michael Black wrote:

Look in old ARRL Handbooks, or even their old Mobile Handbook.

Good afternoon, Michael.

Yeah, I gave away a stack of my old Handbooks a while ago... XYL got tired
of looking at them in the garage (hadn't finished setting up the shack
yet, and still haven't...). :-(

Figure out whether the signal is radiating from the chassis, or from the
output wire. If it's the former, it needs better shielding. If it's
the latter, add feedthrough capacitors in a box that shields the output,
and maybe put an LC circuit in series with the output line, and tune it
for a null. The primary of the inverter may also be a source of noise,
you need to figure that out first.

Well, square waves have a lot of harmonics, and perfect square waves have
infinite harmonics (but there's no such thing as a perfect square wave so
in the real world harmonics are finite). If I can file off the corners of
the stairstep wave that really should help cut down on the harmonics.

Someone emailed me and recommended a brute-force EMI filter (thanks, Dave)
so since that's easiest I'll probably try that first then take things from
there.

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. SNIPPED

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?
-----

It is generally quite easy to construct a filter to eliminate the square wave
component[s] in an approximated sine wave.

First, determine how many steps are used, what is the frequency of the square
wave, in one cycle to make the 'sine' wave?

Second, a three stage pi-filter is designed to severely reduce the conducted
interference.

The first stage is series resonant at the fundamental square wave frequency and
is across the hot line to return [not ground].

The second stage is parallel resonant in the both paths after the series filter.

The third stage is identical to the first stage, but located at the output of
the parallel resonant filter.
--L--
---------------| |---------- [Hot]
L --C-- L
| |
C C
| --L-- |
--------------| |----------- [Return]
--C--
NOTE: The Return must be an isolated wire just like the Hot line. The return
line MAY be connected to inverter chassis by a 'zero current' carrying
connection [approximately 50 Kohms] ONLY at one point.

It will take a little effort to locate suitable cores for the inductive
component. The capacitors can be electrolytic up to several 100 KHz. The key is
to establish RESONANCE at the fundamental component of the square wave.

----

An alternative may be to replace the square wave generator with a simple op-amp
and power stage configured as a WEIN Oscillator. A Wein oscillator has
negligible harmonic component. One op-amp and a couple of transistors should do
the trick.

/s/ DD, W1MCE


Rick (W-A-one-R-K-T) wrote:

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...

Thanks...

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?

Thanks...



I have several solid state inverters (12-24 vdc to 110 vac) and they all
generate serious hash. Doesn't matter what I run; radio, TV, anything
audio, sounded terrible. Been like this for years and years. Inverters
are nice and higher efficiency and for things like incandescent bulbs,
drills, etc. I even ran a small air conditioner off a large inverter
and 24 vdc out in a shed on land where there was no utility power.

I would like to hear from guys who actually built "filters" and got "nice"
AC, as determined by actual performance and not "the fundamentals say you
can do this."

FWIW, FYI....

What I got recently was an old dynamotor from Fair Radio Sales (Lima,
Ohio) that goes from 24 vdc to 110 vac at 60 cps (yes). Its in their
catalog. Its only 50% efficient and puts out about 300 watts of AC at
about 600 watts DC (24 v at about 24-27 amps) input, but the output is
very clean. I tried several radios and no hash at all !!! (I did not
listen on ham bands with RF gain up, but AM radios, on broadcast band even
between stations with volume turned up were clean).

Running full speed, these things sound like an electric drill. For me, its
going to sit in the garage and I'll run an extension cord into the house
if I need this kind of clean AC. Running no load, the dynamotor ddraws the
full 10-12 amps at 24 volts, and as you increase the load, the DC amps go
up in proportion to the load.

The commutators on these units had oxide on the copper and so you need to
rotate the armateur to start scraping off the oxide, then the thing will
take off under DC and the heavy carbon brushes will completely bring a
shine to the copper.

These dynamotors will turn on 12 volts, too, and put out about maybe 50-65
volts AC at a little slower frequency. 60 watt light bulb lights up to a
dim level.

IIRC, they weigh about 50 lbs, cost about $65-70 now.

Out at the end of my driveway i need to use an electric weed eater and so
I load the dynamotor into the trunk of the car, with two deep cycle marine
batteries, and buzz away. Too far for extension cords, no matter how I do
it. Don't like gas engines, noise, flamables, etc.

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.

In article ,
"Brenda Ann" wrote:

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.



How about you just TRASH, all that cheap Inverter JUNK, and spend a few
bucks on a nice SineWave Inverter, in the first place. No Square
Corners to generate harmonics, and nice cleam Ac Power to run the
stuff you need. Myself, I use a nice Trace SW4024 to power the cabin,
and all the stuff that the normal Grid Supplied folks have in their
places. I just can't run the ClothesDryer, without the genset running,
due to it being a 240Vac Load. I usually have a Ambiant Noise Level of
less than 2 S Units on the MF and HF Bands, as well as the Marine Bands.
Never can tell if the Inverter or generator is suppling the power from
the noise level.

Bruce in alaska
--
add a 2 before @