Questions tagged [direct-conversion]
7 questions
19
votes
5 answers
SDR: Quadrature demodulation vs direct RF sampling
I see that many SDRs use a quadrature demodulator and sample I and Q signals.
But is it possible to downconvert the RF signal instead, sample it with only one ADC, and get the same capabilities of digital postprocessing?
So if we want to observe…
BarsMonster - R2AYN
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9
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3 answers
What are the I and Q in quadrature sampling?
For some reason I've long believed that given I and Q, one corresponds to amplitude, and one to phase, so I thought that I could hold one steady and create AM, or hold the other steady and create FM.
Now that I'm delving more into it, though, it…
Adam Davis
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6
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2 answers
What happens when I and Q are switched?
In https://ham.stackexchange.com/a/1068/9 it's shown that one can use
$$ r = \sqrt{I^2+Q^2} $$
to decode AM signals from a direct conversion receiver. It appears that, in this particular case, I and Q are interchangeable, thus the SDR doesn't care…
Adam Davis
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4
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2 answers
Can a Digital Down Converter, at the same time, generate I,Q streams & Downconvert?
A Digital Down Converter (DDC) is usually used to convert Real Digital Signals at a high frequency to baseband (centered around 0Hz). DDC does this so by producing negative and positive frequencies.
However, at the same time, perhaps using an…
Denis
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2
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2 answers
What are best practices against spurious frequencies (birdies) in the superheterodyne design?
One problem I observe with my homebrew superhet receivers/transceivers is the constant presence of several "birdies". From what I know this happens due to the great sensitivity of the receiver and the presence of at least two (depending on the…
Aleksander Alekseev - R2AUK
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2
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3 answers
What causes my direct conversion 80m receiver to receive AM broadcasts?
I am making a Direct conversion receiver from this circuit at this website.
I made it for the 80m band and I changed:
The frequency of VFO to about 1.75 MHz
L1 and L2 to a bandpass filter for 80m
and the VFO coil is not like the one in this…
mathias
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1
vote
2 answers
How is frequency selection (tuning) accomplished in a direct conversion receiver?
How is frequency selection (tuning) accomplished in a direct conversion receiver ? A crystal filter can't be used is that correct ? Because there is no IF to mix with the incoming frequency band ...
Andrew
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