# Tag Info

## New answers tagged modulation

3

If you are "observing" the source, this implies there is some sort of information you are looking to get out of it, whether it be the total background noise, interference levels etc. Do you find "value and use" in the RF signal's magnitude versus time? What about the RF signal's phase versus time? The IQ representation gives us both of ...

1

Are these Tx chain and Rx chains the correct way to implement this transmission? No. When you want to transmit a real cosine in passband, then you need a single complex tone in baseband. Not a real one. Otherwise, you'll have two real tones on the air, one at the mixing frequency + cosine frequency, and one at the mixing frequency - cosine frequency. But ...

2

Despite the great answers by Dan and Olli - I am convinced this is indeed just plain ISI. In my case it's introduced by the droop of the analog filters after the DAC cutting into the passband of my signal. It's pretty clear from my tests that by extending the analog filter cut-off I can remove this effect. Thinking about how that works, the highest frequency ...

0

The analog filter will be more than that such as to minimize further distortion to the passband. The analog filter bandwidth will depend on its purpose (Tx DAC reconstruction, Rx ADC and mixer anti-alias, interference rejection) while the fine passband filtering would be done by the pulse shaping filter in the Tx itself and the matched filter in the Rx, ...

2

If there is capacitance between signal and ground, a resistor-capacitor (RC) filter may be formed. It can also be an intentionally added filter, like in original poster's answer. An RC low-pass filter has an exponentially decaying impulse response. Due to the exponential decay, if the interference from a first symbol to the second symbol is 10 %, then the ...

2

I don’t think this is necessarily additionally introduced ISI (beyond the ISI of the pulse shaping filter itself, which is zero when there is no timing offset), but may be the result of timing offset error. All the points within a small offset from the ideal sampling location appear to be selected, and the overall pattern of the full constellation showing ...

1

Constellation diagrams exist in what is called signal space which is an abstraction used to describe finite-energy signals. The coordinate axes, even if they are marked $x$ and $y$ as in Marcus Muller's answer, really represent unit-energy signals such as $$s_I(t) = \sqrt{\frac 2T}\cos(2\pi f_c t)\mathbf 1_{t \in [0,T)}(t),$$ s_Q(t) = -\sqrt{\frac 2T}\sin(...

0

What I mean is, how do we know what coordinates are to assign to points in the constellation. We don't; you can rotate your PSK however you like it. You can also vary the diameter however you like it. It's all convention. All that PSK means is: "the information is in the phase of the symbols, all other parameters (which is amplitude) are left at a ...

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