Unless you're building the IQ modulator with real signals for
educational purposes, go with the flowgraph Ron mentioned.
Multiplication by a complex sine is much easier. You can also use a
Rotator or Frequency Xlating Filter to do similar things. The bandpass
filter can be built in to the Xlating Filter.
On the additional peaks, the second highest one is about 50 dB lower
than the desired one. From a real hardware point of view, it might as
well not be there (same as 1mW vs 100W). If you use a bandpass filter,
you can make it arbitrarily small, but filtering should be done based on
requirements, not just to make a plot look nice.
- Jeff
On 09/08/2015 01:30 PM, Przemek Lewandowski wrote:
Thank You Jeff for answer.
I have fixed Sampling Rate (of course you were right with it) and
realized that Hilbert Taps was wrong. When Sampling Rate was default
32k, default taps for Hilbert Transform is 64.
So for 48k Sampling Rate for Hilbert Transform should be 96 ?! (Im not
sure about what im writing, but this configuration works as you can see
in image 1 - upper plot)
image 1 - http://postimg.org/image/jme38k5hx/
image 2 - fixed and simplified flowchart -
http://postimg.org/image/ukpcqqu39/
And after all that, I can see there a lot more peaks. So should I filter
them ?
What with that second peak near LSB Peak ?!
Greatings, thank you in advice
Przemek Lewandowski
2015-09-08 18:32 GMT+02:00 Jeff Long <[email protected]
<mailto:[email protected]>>:
Your first problem is that you're using a 32k sample rate with a 20k
sin/cos. This will actually come out as a 12k sin/cos, due to
aliasing. Try the same thing again with a 48k sample rate and see
what happens.
Either bandpass filtering or a Hilbert transform can be used to
create SSB.
Not sure what your flowgraph does, but it looks fun.
Jeff.
On 09/08/2015 08:48 AM, Przemek Lewandowski wrote:
Hi everybody
Im trying to make SSB modulation with Hilbert transform. And Im
using IQ
modulator
here is schema:
http://postimg.org/image/gms5srret/
And I have a question. In Frequency domain there should be one
peak, and
on on my plot there is one - that is good, and second that is
smaller/suppressed.
Is something wrong ?? or is it normal ??
Is Hilbert method for creating SSB signal is good ?? or can it
be made
easier ???
thank you very much.
Przemek Lewandowski
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