"Michael A. Terrell" wrote:

They are "Pure sine wave" only when fed into a purely resistive
load.

That's not true of a modern pure sine wave inverter. I don't know
what link he provided; I'm familiar with Exeltech, which makes the
best inverters out there, IMHO. They use pulse-width modulation to
synthesize the sine wave and are rated at producing that sine wave
into a load of any power factor.

Because they do use PWM, they can generate RF noise, but you can get
optional kits to clean up the RF noise from them. Obviously external
methods can be used as well.

Exeltech claims that they're used in US Embassy radio rooms all over
the world.

Now as for non-sine-wave inverters... most of the ones out there call
themselves "modified sine wave" inverters, which isn't really close to
reality. They put out a modified SQUARE wave, which will have instead
of a zero-crossing point it will have a time at 0V with the leads
shorted together. This is an attempt to make motors run more smoothly
with their power. Nonetheless, everything other than light bulbs will
be noisier and run hotter (or be destroyed) by one of these inverters.
Vaariable-speed drills and light dimmers won't work at all.

Now, these non-sine-wave inverters really do deliver 120 V RMS (or
whatever their rated voltage is), but their peak-to-peak voltage
varies wildly based on the input supply's voltage.

When you power a radio with one, the power diodes at the input
create a nonlinear load: Very heavy at the peaks and no load at lower
voltages. The inverter would have to be run at a very small percentage
of its rating along with some other loading or through a resonant line
filter to help even out the load to the inverter.


A lot of cheap "Wall warts" are built without caps across the
rectifiers which cause them to generate a lot of RF noise and carry it
right to the radio with the DC power. I've got a couple hundred Wall
warts and very few have the extra caps to stop the RF problems. All you
have to do with most of them is plug it in close to a radio and you'll
hear some noise but it's a lot higher if you power the radio from it.

That is true -- however, ICOM line lumps have the holes and traces in
place for the caps inside, so the mod is trivial.

--
Eric F. Richards

"Nature abhors a vacuum tube." -- Myron Glass,
often attributed to J. R. Pierce, Bell Labs, c. 1940

In article ,
Greg wrote:
Yes, I did forget the link:
http://www.innovatronix.com/cgi-bin/...alog/index.asp

These inverters are meant to power photo strobes and apparently are powered
from a car battery, though they don't specifically say so.

I guess the strobes need an especially clean electrical source.

Not strobes, but the incandescent floodlamps. Some of them last under
a hundred hours rated running time and are real picky about the voltage
they run at.

I'm not interested necessarily in the inverters but I was curious about sine
wave vs switching power supplies. I guess a switching supply, powered from
household AC, would be sufficient to power 12VDC radios?

Not if you want to receive anything. You've got basically the same
circuit as a 50-250 watt medium wave transmitter feeding your radio
through the power supply wires via the rectifier and filter.
It's got to be a really GOOD filter. And any consumer grade power
supply isn't going to be that good.

Mark Zenier Washington State resident

From: Telamon
Organization: Internet Argonaut
Newsgroups: rec.radio.shortwave
Date: Sun, 10 Apr 2005 18:58:57 GMT
Subject: Power Supples

In article ,
Greg wrote:

Okay, thanks to all who replied.

The people at

http://www.innovatronix.com/cgi-bin/...alog/index.asp

are marketing these power inverters to run studio strobes on location, which
implies, though they don't actually say so, that they run off a vehicle
battery and supply ample VDC for the studio strobes, which require recycling
large capacitors as rapidly as possible.

My interest would be in using an 12VAC inverter to supply 13VDC voltage for
my NRD-525, in hopes of eliminating power line noise (as well as powering
several potable, battery-operated radios). From what you guys are telling
me, either a linear or switching power supply would work, but filtering is
the critical factor. (This isn't a big priority - most noise at my location
is radiated noise.)

I'll sum up my previous response. Linear or switcher could work in
practice but it would be unlikely and expensive for a switcher supply to
not interfere with radio reception.

Not only do you need to use a linear supply but I would make sure that
supply is radio friendly. Just because it is a linear supply it does not
mean that the designer has gone through the trouble to provide an RF
bypass around the rectification diodes, which still create switching
noise even at lower voltages.
+++++++++++++++++++++++
You can find out if your reception noise floor is affected by EMI by
disconnecting the antenna and tuning slowly through all the bands you
want to listen too. This will allow you note down any birdies the radio
may have and at what level along with whether any conducted noise is
coming through the power cord.

You should terminate the antenna terminals 50 ohm input with a short
lead 50 ohm resistor in practice but it probably won't make a difference
in this test.

You can then reconnect the antenna and note the difference in noise. In
this way you can determine the difference in EMI and RFI at your
location instead of guessing.

--
Telamon
Ventura, California

Good advice. Thanks Teledude!

Greg

From: David
Organization: EarthLink Inc. -- http://www.EarthLink.net
Newsgroups: rec.radio.shortwave
Date: Sun, 10 Apr 2005 19:12:24 GMT
Subject: Power Supples

On Sun, 10 Apr 2005 17:47:40 GMT, Greg wrote:

Okay, thanks to all who replied.

The people at

http://www.innovatronix.com/cgi-bin/...alog/index.asp

are marketing these power inverters to run studio strobes on location, which
implies, though they don't actually say so, that they run off a vehicle
battery and supply ample VDC for the studio strobes, which require recycling
large capacitors as rapidly as possible.

My interest would be in using an 12VAC inverter to supply 13VDC voltage for
my NRD-525, in hopes of eliminating power line noise (as well as powering
several potable, battery-operated radios). From what you guys are telling
me, either a linear or switching power supply would work, but filtering is
the critical factor. (This isn't a big priority - most noise at my location
is radiated noise.)

Greg

Why all the riggamarole? Why not just run the radio off the
aforementioned vehicle ballery?

I was considering a more permanent power supply to run the radio at home
independent of the house wiring. So, I wasn't considering using the
Innovatronix inverters, but their description lead to my question about
"sine wave" (prob meaning "linear") vs switching power supplies. Also, I
thought the Innovatronix gear might be of some interest to the group here.

I guess I wasn't too clear.

Greg

Cuhulinman - See my reply to David's post. I'm really just trying to learn
a little about power supplies, and was wondering if a power supply in my
shack would eliminate power line noise from the house. The inverters I
mentioned are not what I would use at home, but they brought up the question
of what's the difference between switching and linear.

I could use batteries, but I want a more permanent solution in the shack.
Though, it's likely that power line noise is minimal compared to radiated
noise picked up by my antenna, so I probably really don't need a separate
power supply.

Greg

From:
Organization: WebTV Subscriber
Newsgroups: rec.radio.shortwave
Date: Sun, 10 Apr 2005 15:21:17 -0500
Subject: Power Supples

Use two 12 volt car batteries and an a voltage drop thingy of the right
amount of voltage drop.Or is that practical?
cuhulin

On Mon, 11 Apr 2005 01:32:32 GMT, Greg wrote:



From: David
Organization: EarthLink Inc. -- http://www.EarthLink.net
Newsgroups: rec.radio.shortwave
Date: Sun, 10 Apr 2005 19:12:24 GMT
Subject: Power Supples

On Sun, 10 Apr 2005 17:47:40 GMT, Greg wrote:

Okay, thanks to all who replied.

The people at

http://www.innovatronix.com/cgi-bin/...alog/index.asp

are marketing these power inverters to run studio strobes on location, which
implies, though they don't actually say so, that they run off a vehicle
battery and supply ample VDC for the studio strobes, which require recycling
large capacitors as rapidly as possible.

My interest would be in using an 12VAC inverter to supply 13VDC voltage for
my NRD-525, in hopes of eliminating power line noise (as well as powering
several potable, battery-operated radios). From what you guys are telling
me, either a linear or switching power supply would work, but filtering is
the critical factor. (This isn't a big priority - most noise at my location
is radiated noise.)

Greg

Why all the riggamarole? Why not just run the radio off the
aforementioned vehicle ballery?

I was considering a more permanent power supply to run the radio at home
independent of the house wiring. So, I wasn't considering using the
Innovatronix inverters, but their description lead to my question about
"sine wave" (prob meaning "linear") vs switching power supplies. Also, I
thought the Innovatronix gear might be of some interest to the group here.

I guess I wasn't too clear.

Greg

Build a nice beefy TransformerFullWave BridgeChoke Input Filter DC
Power Supply With Very Low Ripple. Then use a Premium Quality Low
Noise DCC Coverter for each radio.