Here's a line of power inverters marketed to photographers, but possibly of
interest for use with radios. They offer "pure sine wave" inverters as well
as cheaper switching power supplies.

What's the difference, in layman's terms, between sine wave and switching
power supplies? What are the pros & cons for practical applications?

I've always wondered if the switching power supplies, like the Radio Shack
models, that convert 120VAC to 13VDC, are appropriate for radios.

Thanks,

Greg

Greg,

It looks like you forgot the link, but I have some comments anyway.

Pure sine inverters often provide power that's even "cleaner" than the juice
coming directly from the AC wall outlet, and this is great for sensitive
devices like computers and audio equipment.

I bought a new pure sine inverter at a good price on Ebay last year and put
it to extensive tests. My goal was to use it to power a Racal RA6790GM on
DC-only DXpeditions with my other equipment, and hopefully avoid the noise
and RFI present with garden-variety inverters.

Well, my friend Craig at Kiwa Electronics told me that pure sine inverters
can still be sources of radiated noise that interfere with radio reception,
and I found this to be sadly true. I had a deep cycle battery and the pure
sine inverter completely sealed in a metal box, and separated from my DXing
van by 35 feet of shielded, 3-conductor 16-ga cabling. The box was tried
grounded and ungrounded. I also added RFI surpression ferrite chokes inside
the pure sine inverter's enclosure on the input & output leads. My Beverage
antenna's feedline (with grounded shield) and isolated matching transformer
were in the opposite direction, as far as possible from the inverter &
battery box. I also used a high quality Bussman line conditioner between the
receiver and pure sine inverter's output.

Unfortunately no matter what arrangement I tried, I still had bothersome RFI
on most shortwave bands and throughout mediumwave. In this quiet DXpedition
location, *any* noise is noticeable. I had to give up on the Racal during
the DXpedition and use my modded R-75 on DC only.

I noted that all of the noise (in this case) was RADIATED noise, not
conducted through the Racal's power cord. When I disconnected the antennas,
the noise went away. I believe that the 3-conductor "shielded" cable and/or
metal box was the culprit; they radiated the RFI despite the grounding.

Bottom line: pure sine inverters are great for protecting delicate gear, but
they still create external noise that can be picked up by nearby antennas
:^(

Guy Atkins
Puyallup, WA USA



"Greg" wrote in message
...
Here's a line of power inverters marketed to photographers, but possibly
of
interest for use with radios. They offer "pure sine wave" inverters as
well
as cheaper switching power supplies.

What's the difference, in layman's terms, between sine wave and switching
power supplies? What are the pros & cons for practical applications?

I've always wondered if the switching power supplies, like the Radio Shack
models, that convert 120VAC to 13VDC, are appropriate for radios.

Thanks,

Greg

Sine wave Inverters (from what I have read about them before) provide a
cleaner,smoother output of electricty that is better for electronic
devices.I bought an 800 Watt sine wave inverter for $100.00 from a
company in Jackson about ten years ago.I gave it to my brother in law.I
have a few small inverters here like the kind that stores such as wal
mart stores and similar stores and auto parts stores sell.
cuhulin

A low B Flat on a portable synthesiser coupled to a 12 volt amp?

On Sat, 9 Apr 2005 13:08:16 -0500, wrote:

Sine wave Inverters (from what I have read about them before) provide a
cleaner,smoother output of electricty that is better for electronic
devices.I bought an 800 Watt sine wave inverter for $100.00 from a
company in Jackson about ten years ago.I gave it to my brother in law.I
have a few small inverters here like the kind that stores such as wal
mart stores and similar stores and auto parts stores sell.
cuhulin

David ) writes:
A low B Flat on a portable synthesiser coupled to a 12 volt amp?

Well that's the general idea, a sine wave oscillator feeding an audio
amplifier.

A square wave inverter is only on or off, so efficiency is better.
But of course, it has lots of harmonics from the square wave, which
of course can interfere with reception. There's also the issue of
whether the equipment that is powered from it can handle it. The
square waves may not be good for specific pieces of equipment.

I"m not even sure what this is about. A shortwave radio, if it
uses an external power supply, is not going to need an inverter.
You either power it with batteries (a separate stash, or filtered
from a car battery), or an AC adaptor. Current demand is not
so high that a regular transformer power supply will be too bulky,
so there's no need for anything fancy.

The only case one needs an inverter for shortwave receivers is if
the receiver has a built in supply, and now way of powering from
an external DC supply.

Michael

Greg wrote:

Here's a line of power inverters marketed to photographers, but possibly of
interest for use with radios. They offer "pure sine wave" inverters as well
as cheaper switching power supplies.

What's the difference, in layman's terms, between sine wave and switching
power supplies? What are the pros & cons for practical applications?

I've always wondered if the switching power supplies, like the Radio Shack
models, that convert 120VAC to 13VDC, are appropriate for radios.

Thanks,

Greg

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

--
Former professional electron wrangler.

Michael A. Terrell
Central Florida

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.

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?

Greg

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.

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?

Greg


Some are and some aren't. They work OK if they are designed for low
noise but the price isn't the best indicator. The 700/ 1600/1620 series
Telemetry recievers we built at Microdyne went through a number of pwer
supply vendors because of noise and reliability problems. We went
through a whole series of tests on each sample power supply, selected
the best and pratyed they didn't change the design before we had a
replacment supplier ligned up. These were in the $700 to $1000 dollar
range for just the power supplies.

--
Former professional electron wrangler.

Michael A. Terrell
Central Florida

Greg ) writes:
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.

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?

Greg


I think then you may be misreading things.

Traditionally power supplies were "linear", ie the AC line was fed into
a transformer which raised or lowered the voltage as needed, and then
that voltage was rectified and filtered, and sometimes regulated. They
become problematic when high current is needed, because then the transformers
are bulky. For receivers, that should never be a factor, and there
is no reason to not use a linear power supply.

Switching supplies take the AC line, and rectify it, then use that to
power a power oscillator running on frequencies above the audio range.
This means that the transformer to make this a lower voltage (and
usually it will be a lower voltage) can be smaller since it is
running at a frequency in the tens of KHz range rather than the 60 Hertz
of the AC line. Filter capacitors can also be smaller for the same current,
since again it is filtering a much higher frequency. This sort of
supply is used where high current is needed, such as tv sets or
transmitters, though since they do generate high frequency square
waves, much attention needs to be paid to keeping it inside the box,
or else you will get interference.

A DC to DC inverter is the same basic idea as the switching supply,
except it takes DC at the input to power the oscillator. A square
wave one is simple, since you can have a power oscillator with two
power transistors. These were common in the sixties, when tube
equipment was still common in cars, taking over from vibrator
power supplies. The latter used a mechanical system to switch
the incoming DC on and off at a high audio rate, to feed a power
transformer.

But when a DC to DC inverter was needed that put out a sinewave,
it was no longer a simple task. As I said, you'd need a sine
wave oscillator, and then feed that into an audio amplfier,
and often feed that into a transformer to boost the voltage up or
down.

I'm not sure why strobes would need a sinewave for charging.

Michael

In article ,
Greg wrote:

Here's a line of power inverters marketed to photographers, but possibly of
interest for use with radios. They offer "pure sine wave" inverters as well
as cheaper switching power supplies.

What's the difference, in layman's terms, between sine wave and switching
power supplies? What are the pros & cons for practical applications?

I've always wondered if the switching power supplies, like the Radio Shack
models, that convert 120VAC to 13VDC, are appropriate for radios.

Those terms are for different things. Sine wave is the form or shape of
the voltage output from a supply. A switching supply is a circuit design
type that may or may not produce a sign wave.

The two main types of AC to DC supplies are linear and switching. A
linear supply will use a large and heavy, compared to a switching type,
transformer to step the voltage down and provide isolation from the AC
mains supply. The stepped down voltage is rectified, filtered and then
followed by a series linear voltage regulator. A switching supply has a
high voltage rectification bridge followed by the switching transistors
and transformer. The secondary side of the switcher is rectified
filtered and then a sample of the resulting DC voltage goes to a PWM
chip controller, which generates the the pulse that turns the front end
switching transistors on and off. The frequency of the switcher is
usually fixed for a design and the power transferred through the
transformer is controlled by the amount of time those front end
transistors are on, which is determined by the controller pulse width.
For isolation reasons the switching control pulse has to go through its
own small transformer from the secondary side back to the primary side.
Very small and cheap switchers use an Opto-isolator chip in place of the
small pulse control transformer.

What does all this information mean between linear and switching
supplies? Well, there are fewer opportunities for the simpler linear
power supply to generate radio interference and the switcher has many
more so the end result is that a linear supply will be quieter than a
switcher. The linear has its rectification and voltage regulation done
at lower voltages where the switcher does both at high voltage. Worse
the switcher is designed for fast on and off times for efficiency
reasons. High voltage and fast switching is a recipe for noise
generation. You could make the switcher as quiet as the linear but it
would cost a lot of money to make it.

Bottom line is the switcher will be more efficient, smaller and lighter
for the DC power it can deliver compared to a linear supply. The linear
supply will generate less conducted (EMI) and radiated (RFI) radio noise.

The noise may not bother cameras but can interfere with radio reception.

+++++++++++++++++++++++++++++++++++++++++

Now lets talk about AC to AC supplies, which is the sine wave question.

The linear way of controlling AC in and out in a linear fashion is a
transformer of some type. Some are designed to accept a small range of
input voltage variation and produce a fixed output voltage. These are
auto-transformers. No noise is generated with these units since there is
no switching. These are big, heavy and work for a limited input voltage
range. The wave shape in is the wave shape out.

Much more complex is the UPS or uninterruptible power supply. Where the
AC is converted to DC in order to charge the batteries. This AC to DC
could be linear or switching type. Now comes the "pure sine wave"
question. The DC needs to be converted back to AC. The simplest is a
square wave produced by high power transistors turned on and off at
60Hz. This is usually to raw for most electronic devices using AC power
so it is followed by some simple filtering. This then produces a
trapezoid waveform, which is the square wave with much slower rise and
fall time edges. Some electronics like computers will operate without a
problem with this type of waveform but many devices may have some
problems. For more sensitive electronics employing a higher rate of
switching than 60Hz can allow you construct the sign wave in a step like
form. The higher the switching frequency the smaller the steps and the
closer to a perfect sine wave you will produce. Draw a sign wave on a
piece of paper and then do the same thing using a stair case pattern
going up for the rise time and a stair case going down for the fall time
and that is what you would see with an oscilloscope.

There are obviously many opportunities for switching noise generation
and it would be a very expensive actively controlled AC to AC or UPS
type of unit to not generate plenty of radio noise.

I could go on but this is probably way more than you want to know
already.

--
Telamon
Ventura, California