Maybe this is not a good forum to ask this question, but some electronics guru please provide some suggestions to my problem ? I am experimenting with a QPSK modulator - demodulator system, and my question is: if the data bits are arriving at 1 MHz, what would be an ideal carrier frequency ? I think the Nyquist criteria should hold, but somewhat confused. Any hints, suggestions would be of great help. Thanks in advance.
Cripes. What do you mean "Nyquist criteria should hold?" And "ideal" in what sense?
Anyway, look at these?
And for some thoughts about one way of looking at "ideal," here's one I recently read:
Jon
It's an ill-posed question... you're asking something along the lines of, "if my car has a top speed of 45mph, what's the ideal route from Dallas to Houston?" -- You might be able to eliminate certain answers (e.g., "taking the interstate probably wouldn't be wise" / "using a carrier under 10MHz probably wouldn't be wise"), but the answer you seek needs rather more inputs than what you've provided to be answered in a meaningful sense.
Old Bell 201 modems managed 2400 bps QPSK with a carrier of 1200 Hz, or something like that.
In theory, you could transmit 10K bits/sec on a 1 KHz carrier, if the s/n was good enough.
John
Huh?
For QPSK, a frequency of 0 is just as good as the frequency of -1. Even a complex frequency of j would work.
VLV
Well, I just said it wasn't wise, not that it couldn't be done -- you certainly can drive from Dallas to Houston at no more than 45mph on the interstate. :-)
OK, the relative difficulty in my analogy was perhaps rather far off...
Driving from Dallas to Houston isn't much fun anyhow.
John
"if
the
probably
what
Constellation modulation does routinely pack, say, 16 bits into one cycle of carrier. But it has more states than QAM. One example is a
56K modem that works over a 3 KHz voice-grade line.John
"if
the
probably
what
What a gibberish.
A semi-truck can routinely put, say, 40 tons, onto a rubber tire. But the truck has more carrying capacity then the GMC. One example is a locomotive which can carry 100 carriages over two steel rails.
VLV
"if
the
probably
what
Constellation modulation is gibberish?
I don't think so.
But
Now *that's* genuine gibberish!
John
Yes. "Constellation modulation" has no meaning whatsoever.
The genuine gibberish is when someone talks about the things without having a clue.
VLV
Google disagrees. So does the US patent office.
Look up truck tire capacities. There is lots of stuff on the web. The biggest truck tire I could find was good to about 6 tons, and that's unusual.
Even if you could load a truck tire to 40 tons, which you can't, it would be illegal to drive it on any highway in the country. 7 tons per axle is a typical limit.
John
"if
the
probably
what
Are you trying to keep the cheap Russian Vodca distilleries in busness by yourself?
One tire? Bullshit. Why do you think 'Tractor Trailers' have 18 wheels?
GMC? Do you mean GVW?
No, the weight is carried by the rails to the railroad ties and finally to the road bed. It wouldn't matter if a train was just one engine and one car, or 50 engines and 100 miles long. The weight per square inch on the roadbed is the same, if the cars have the same load.
-- For the last time: I am not a mad scientist, I'm just a very ticked off scientist!!!
-- For the last time: I am not a mad scientist, I'm just a very ticked off scientist!!!
I've touched (but not ridden in, and certainly not driven, a 150-ton mining truck--four tires. Of course they were considerably taller than I am. ;)
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal ElectroOptical Innovations 55 Orchard Rd Briarcliff Manor NY 10510 845-480-2058 email: hobbs (atsign) electrooptical (period) net http://electrooptical.net
Have you ever seen a Slag Hauler at a steel mill? :)
-- For the last time: I am not a mad scientist, I'm just a very ticked off scientist!!!
That's not really a truck, so I guess it does qualify as a "semi- truck"
And that's still just 37.5 tons per wheel!
But I still don't get either of the analogies.
John
Not a truck tire, but pretty impressive (the tire alone is 1500lbs - total load >100T/tire):
Is that the kind of tire Dimmie likes to chew on?
-- For the last time: I am not a mad scientist, I'm just a very ticked off scientist!!!
QAM is "Constellation modulation"
Also case 56K modems (V.90) don't use QAM on the 56K channel. 36K (V.34) did
-- ?? 100% natural
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