Wind/Solar Electrics ???

You can represent the bandwidth with double the
sampling rate as the bandwidth frequency but there is a
component missing from the sample information that has
to be known and is not part of the samples. Namely the
base frequency has to be added back into the formula.


"daestrom" wrote in
message
...

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

In article ,
"daestrom" wrote:

"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



You are getting your terms confused here guys. Nyquist requires that
you input both the Center Frequency, and Bandwidth when determining
the Sampling Rate. If the sampling is done at BaseBand then only the
Bandwidth is relevent. If the sampling is not done at baseband, then
the Center Frequency, and Bandwidth are required to determine samling
rate. Example, if the Bandwith of the signal is 3Kc and the sampling is
done at BaseBand then sample rate needed would 6Kc. If the sampling is
done at 100 Mhz with the same 3Kc bandwidth, then a 200.006 Mhz sampling
rate would be required.

It is much easyier to do DSP at baseBand, than at IF Frequencies, and if
you do DSP at IF Frequencies, the lower the IF Frequency, the easyier it
is to do, and the slower the DSP has to run.

Me

If only the baseband frequency is sampled at 6kHz then
information is missing to recreate the original 100kHz
and the sampling information is insufficient to
recreate the original signal.


This is analogous to saying the number 1234 can be
represented by
(1234-234) / 1000 = 1

If I supply the number 1.0 you can regenerate the
number 1234 from it? Not true, without the rest of the
sampling information. The sample is incomplete.

Bandwidth sampling only cannot recreate the original
signal.

"Me" wrote in message
...
In article
,
"daestrom"
wrote:

"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



You are getting your terms confused here guys.
Nyquist requires that
you input both the Center Frequency, and Bandwidth
when determining
the Sampling Rate. If the sampling is done at
BaseBand then only the
Bandwidth is relevent. If the sampling is not done
at baseband, then
the Center Frequency, and Bandwidth are required to
determine samling
rate. Example, if the Bandwith of the signal is 3Kc
and the sampling is
done at BaseBand then sample rate needed would 6Kc.
If the sampling is
done at 100 Mhz with the same 3Kc bandwidth, then a
200.006 Mhz sampling
rate would be required.

It is much easyier to do DSP at baseBand, than at IF
Frequencies, and if
you do DSP at IF Frequencies, the lower the IF
Frequency, the easyier it
is to do, and the slower the DSP has to run.

Me

On 23 Dec 2005 23:57:27 -0800, 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

He previously wrote about using either a 150 Ohm rheostat (other times
referred to as 150A or 200A), or 300k nichrome wire to control a few
Amps of field current on a small 12V automotive alternator. According
to the "designer" (who often refers to himself as a "solar power
consultant"), 150 Ohms didn't allow sufficiently low output, hence the
need for the nichrome wire. And as we all know, the prime
consideration on a home-power generator is low output. snorf Similar
wisdom surely underpins his other projects. For instance, liberal
application of 300k wire might be useful when building a max 150, peak
300, zero Watt inverter, or most any zero Watt inverter for that
matter. Perhaps strung around the property in large coils like razor
wire at Slinky Manor. ;-)

Wayne

Take the credit when you can as it does not happen that often.

wmbjk wrote:
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

Which part don't you understand

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

I'll pay that. Thank you for the correction. Spent too many hours under
the car, I guess.

daestrom wrote:
"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

On Thu, 22 Dec 2005 20:36:17 GMT, "daestrom"
wrote:


"Roger" wrote in message
.. .
On Wed, 21 Dec 2005 14:29:00 GMT, Matt Whiting
wrote:

George Ghio wrote:

Tell us why anyone would modify a sine wave.

To vary the power delivered to a load. Chopping off part of a sine wave
cycle is a standard means of power control.


That makes three phase SCR (Silicon controlled rectifiers and not
saturable core reactors) interesting as chopping off part of the wave
form develops spikes and harmonics that tend to make the control of
one phase interact with the others.

I've built a lot of them for single phase control, but I never once
was able to build one for three phase that didn't interact. Turn one
up and maybe another would go up, Turn the second down and the other
two might go up or down. Twas interesting:-)) which is probably why
Saturable core reactors are so popular in industry. Now there is a
controller that is a tad on the weighty side.


Also, some old systems used self-saturating reactors (magnetic amplifiers,
'magamps') for instrumentation. Things could take some severe environments,
but calibration tended to drift a lot. Required fairly frequent 'trip &
cals' to keep them in spec.

For the small and large stuff we used solid state SCRs while the
intermediate still used saturable core reactors. 10 years ago I think
they still had some mag amps, but the ones we had were pretty stable.

They use larger SCRs now, but I have the silicon wafer out of one that
is over 1 1/2" in diameter. They operated up to 480 and 1000 Amps
and ran near maximum for many hours. The SCRs themselves were about
the size of a hockey puck or slightly larger.

Now there was some power and I'd guess they use much larger systems
now.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com

daestrom

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.

No, that's the whole point of this discussion.

You have to understand aliasing. The signal you want aliases
down into the baseband. Your anti-aliaising filter has
to get rid of all the junk you don't want. In this case it
includes the baseband. Since there is no baseband signal
(or other out-of-band junk) you can reconstruct the original
signal.

It's a common trick with software radios.

You do need some extra information that doesn't go in through
the A/D channel. That's the design of the system, in particular
what the anti-aliasing filter lets through.

Maybe the reason that this is so confusing is that you also need
that info the the normal/baseband case. But since that's the normal
case we don't bother mentioning it.

--
The suespammers.org mail server is located in California. So are all my
other mailboxes. Please do not send unsolicited bulk e-mail or unsolicited
commercial e-mail to my suespammers.org address or any of my other addresses.
These are my opinions, not necessarily my employer's. I hate spam.

On Sun, 25 Dec 2005 17:50:50 +1100, George Ghio
wrote:

"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.

daestrom wrote:
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

I'll pay that. Thank you for the correction. Spent too many hours under
the car, I guess.

OHMYGOD! A blunder admitted! Who the hell are you and what have you
done with George Ghio?

Wayne

PS It's in everyone's best interest that you not be found out, so
don't forget to hide your pod.