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#121
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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 |
#122
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Wind/Solar Electrics ???
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 |
#123
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Wind/Solar Electrics ???
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 |
#124
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Wind/Solar Electrics ???
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 |
#126
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Wind/Solar Electrics ???
"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 |
#127
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Wind/Solar Electrics ???
"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 |
#128
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Wind/Solar Electrics ???
"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 |
#129
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Wind/Solar Electrics ???
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 |
#130
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Wind/Solar Electrics ???
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 |
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