Wind/Solar Electrics ???

What do you think it means?

Nick

I've seen a 5% total harmonic distortion spec. How many steps is that?

Try it out? I got a local dealer to start up an EU2000 and run it with and without a muffler.

Nick

It means that perfect reconstruction of a signal requires sampling at at least twice the _bandwidth_ of the signal present to insure that no aliasing occurs.

Two important points here:

---Joel

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.

Hi Ray!

Hmmm... no, I'm not a pilot, I just got sucked in by the cross-posting (starting from sci.electronics.design) and the topic has drifted considerably since it started.

Yes it is... I suspect that's why that projects such as GNURadio (which sub-samples using something like 80 or 100MSps ADCs) tend not to be as sensitive as more traditional analog receivers. (Someone made the comment that the FM decoder in GNURadio doesn't really even work as well as a $5 transistor radio, which is true enough albeit perhaps missing the point of how cool/fun it is to be able to write any modulator/demodulator you like if you're not looking for the ultimate sensitivty.)

I believe that folks who think you need to sample at 200MHz (the intuitively reaosnable answer) are those who were never made to /had the opportunity to open up an undergraduate signals & systems book. :-) Thinking about things like modulation are so much cleaner in the frequency domain once one gets the whole "multiplication in one domain is convolution in the other" bit down.

---Joel

More than twice the bandwidth.

Best regards, Spehro Pefhany

With risers it is the same confusion.

to point at the three

most people count steps,

right-to-left in

case, but step 2 is

in

One might say "the highest frequency present" is the highest frequency non-zero component of the power spectrum.

Nick

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

Hey Joel, what are you doing over here. Are you a pilot too?

I've used this for subsampling, although you have to be very careful of clock jitter when you sub-sample. a couple picoseconds of jitter on the sampling of a 100 MHz signal is going to add substantial noise to the signal.

(subsampling, for those here who haven't a clue what we are talking about...this is an airplane owner's forum after all...is taking advantage of the nyquist theorum to sample at less than the frequencyt of the signal when the bandwidth of the signal is narrow. For example, if you have a signal centered at 100 Mhz that only has a 10 MHz bandwidth, you can sample it at something less than 100 MHz and still recover all of the information. The more generally held belief is that you would need to sample it at greater than 200 MHz in order to not lose information).

You can use a college education in Electrical Engineering, and $40K worth of test equipment, to "KNOW FOR SURE"...... or you can fool around and see what works........ or you can ask one who already did the previous, and figured it out, and then actually believe what they tell you........ other than that your on your own......

Me

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.

A lot of folks mistake it to think you need to sample at least twice as fast as the 'signal of interest' also, and try to ignore high frequency components of the input because they're 'not interested in that noise'. But what Nyquist proved was that any frequency in the sampled signal that is more than 1/2 the sample frequency will 'alias' and 'wrap around' and be

For example, if sampling at 1000 hz, and the sampled signal is a 900 hz 'pure sine wave', the sampled data would look *exactly* the same as if you had sampled a 100 hz 'pure sine wave'. They would be 'indistinguisable'. So if/when you try to convert the sampled data back to analog, how do you know whether it should reconstruct a 100 hz wave, or 900 hz? You don't, so you have a conundrum.

So, to avoid losing this 'information' of being able to tell if you had a

And as Joel mentioned earlier, since most low-pass filters do not have perfect 'cutoff' (IIRC, simple first-orders 'roll off' at something like 3 db/decade), it is more common to eliminate any frequency component that is more than about 40% of the sampling frequency.

daestrom

I'm still scratching my head over that one.

NT

IIUC that woudl demodulate the signal too?

NT

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

Why do you give buyers so little credit? And where does one buy a

Wayne

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

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.

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.

I buy inverters from known manufacturers who are willing to provide spec sheets that out line the full parameters of the inverter. You know things like:

Efficiency curves Max continuous output

Well everything really.

I did build a kit inverter, once, years ago. It had a max rating of

It had a half hour rating of 0W

And a surge of about 300W

Still it did the job it was built to do for many years.

Put your supplier > "MSW is a shysters sales pitch which misrepresents the product. "

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