Hi,

I am looking for someone to guide me in building an IQ modulator/demodulator using QPSK. Any circuit diagrams, links to good websites, recommended books or explanations would be greatly appreciated!

Many Thanks

 

Hello,

Take a look at this page:
http://zone.ni.com/devzone/cda/tut/p/id/5657

Greetings,
Bertus

 

As I get older, my IQ naturally modulates. Generally downwards.

 

Thanks very much for the help... However, I do have a few more questions. It states on the diagram on the website that the signal has to be directly upconverted (DUC) and then mixed with signals from the local oscillator for the modulation of the signal.

Isnt this redundant? If not, why would both steps be necessary because mixing the signals is upping their frequency anyway?

The other question is would this method be the same if I were to do it using QPSK method? If there are differences would you mind to please tell me what they are.

Thanks very much

 

Thanks very much for the help... However, I do have a few more questions. It states on the diagram on the website that the signal has to be directly upconverted (DUC) and then mixed with signals from the local oscillator for the modulation of the signal.

Isnt this redundant? If not, why would both steps be necessary because mixing the signals is upping their frequency anyway?

The other question is would this method be the same if I were to do it using QPSK method? If there are differences would you mind to please tell me what they are.

Thanks very much

Good questions. To answer the second one first, yes, this principle is used for QPSK, or any number of PSKs.

To answer the first question...this scheme, as "redundant' as it seems, guarantees that the signal keying occurs precisely at the Zero Crossing, (integral cycle keying). This yields the least possible bandwidth. Absolute phase relation is maintained throughout the process.

eric