Wind/Solar Electrics ???

On Sat, 24 Dec 2005 09:31:50 +1100, George Ghio
wrote:


One test is the "Modified Square Wave" test.

When you hear these words you know you are dealing either with a shyster
or an ignorant person who should not be selling things he does not
understand.

The only thing your test proves is that you're irrationally
judgmental.

It is hard, what with a flood of imports at bargain basement prices.

Still, as long as people are willing to believe that a $59 3000W
"modified sine wave" inverter from Walmart, Cost Co, etc, etc has the
same specs as a $900 3000W sine inverter is, at best, fooling themselves.

Why do you give buyers so little credit? And where does one buy a
3000W sine-wave inverter for $900?

Wayne

On Sat, 24 Dec 2005 09:33:02 +1100, George Ghio
wrote:

On 22 Dec 2005 19:49:37 -0800, "philkryder"
wrote:

What can we use to "know for sure" that the wave form of a device is
adequate BEFORE buying it?

wmbjk wrote:

I've purchased a couple of ~$1500 machines from a local welding
supplier on condition that if there were any problems running them off
my SW inverters then the machines could be returned in as-new
condition the following day and I'd buy a different model instead.
That flexibility, and being able to see the machines in person, made
the extra cost of buying locally worthwhile.

Wayne

A fine example of the correct approach.

Oh crap. Since your agreement has to be counted as a negative, now
anyone reading will have to wait for someone credible to concur.

Wayne

George Ghio wrote:

I did build a kit inverter, once, years ago. It had a max rating of
150W, Which it met.

It had a half hour rating of 0W

And a surge of about 300W

I'm still scratching my head over that one.


NT

Joel Kolstad wrote:
wrote in message
...
Joel Kolstad wrote:
1) It's the bandwidth of the signal that matters, not the highest frequency
present...
One might say "the highest frequency present" is the highest frequency
non-zero component of the power spectrum.

Sure, but the point is that you can sample a signal that's has all (of a good
approximation thereof, e.g., 99%) of its energy between 144-148MHz (this is
the 2m amateur radio band) at 10MSps and recover everything. I.e., the
bandwidth of the signal is only 4MHz, so you only have to sample at something
8MSps.

IIUC that woudl demodulate the signal too?

NT

wrote:
George Ghio wrote:


I did build a kit inverter, once, years ago. It had a max rating of
150W, Which it met.

It had a half hour rating of 0W

And a surge of about 300W


I'm still scratching my head over that one.


NT


That's standard with george's posts. Don't get a splinter.

--
Steve Spence
Dir., Green Trust, http://www.green-trust.org
Contributing Editor, http://www.off-grid.net
http://www.rebelwolf.com/essn.html

"Joel Kolstad" wrote in message
...
wrote in message
...
Joel Kolstad wrote:
1) It's the bandwidth of the signal that matters, not the highest
frequency
present...
One might say "the highest frequency present" is the highest frequency
non-zero component of the power spectrum.

Sure, but the point is that you can sample a signal that's has all (of a
good approximation thereof, e.g., 99%) of its energy between 144-148MHz
(this is the 2m amateur radio band) at 10MSps and recover everything.
I.e., the bandwidth of the signal is only 4MHz, so you only have to sample
at something
8MSps.


Only if you demodulate the signal first.

daestrom

"Spehro Pefhany" wrote in message
...
On Fri, 23 Dec 2005 18:46:49 GMT, the renowned "daestrom"
wrote:


wrote in message
...
Joel Kolstad wrote:

(I can't tell you how many times I've seen people stating something
like,
'The Nyquist theorem requires sampling at at least twice the highest
frequency present in the signal," when of course it says no such thing.)

What do you think it means?


Nyquist figured out that higher frequency components of the input signal
will 'alias' and you will lose the ability to tell them from lower
frequency
components. In order to avoid 'losing information' and not being able to
tell whether a particular sample stream was from a low or high frequency
component, Nyquist's theorem states you must sample at least twice as fast
as the highest component present.
snip

More than twice the bandwidth.



So, if I have a signal with a 1000 hz carrier, with a bandwidth of 50 hz,
you think I can sample it at just 150 hz and get accurate reproduction?
That's just wrong.

It is the maximum frequency component in the signal that is important. The
bandwidth is not related unless the lower edge of the band is at 0 hz
(whereupon the upper side of the band is equal to the max frequency).

daestrom

"George Ghio" wrote in message
...
Yes this is the problem. While there are people who will tell you anything
to make a sale, how do you know what you are really getting.

One test is the "Modified Square Wave" test.

When you hear these words you know you are dealing either with a shyster
or an ignorant person who should not be selling things he does not
understand.


Judging from your previous posts, I think you mean when you hear "Modified
*sine* wave", then you know you are dealing with shyster or an ignorant
person...."

A salesperson that says their unit puts out a modified *square* wave would
be a sign[sic] of a knowledgable salesperson.

daestrom

Off your medication again Steve?

"Steve Spence" wrote in
message ...
wrote:
George Ghio wrote:


I did build a kit inverter, once, years ago. It had
a max rating of
150W, Which it met.

It had a half hour rating of 0W

And a surge of about 300W


I'm still scratching my head over that one.


NT


That's standard with george's posts. Don't get a
splinter.

--
Steve Spence
Dir., Green Trust, http://www.green-trust.org
Contributing Editor, http://www.off-grid.net
http://www.rebelwolf.com/essn.html

Simple hetrodyne system will do that. No demodulating
required.

"daestrom" wrote in
message
...

"Joel Kolstad" wrote
in message
...

Sure, but the point is that you can sample a signal
that's has all (of a
good approximation thereof, e.g., 99%) of its
energy between 144-148MHz
(this is the 2m amateur radio band) at 10MSps and
recover everything.
I.e., the bandwidth of the signal is only 4MHz, so
you only have to sample
at something
8MSps.


Only if you demodulate the signal first.

daestrom