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Need help with QPSK Demodulator

I've tried to realise the following circuit:

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from this article:
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to demod a QPSK signal. I've tried using an AD8347 (Evaluation Board), but i'm not able to retrieve the "terms at twice the rate of the oscillator". All I can get from the outputs are the difference between the RF and LO, both I and Q.

I'm using an (tunable) RF at 1.44GHz and LO at the same frequency. The LO is generated by ADF411xEB1. Even when I try to tune the RF as close to the LO, the "terms at twice the rate of the oscillator" never appears.

Is this becaues the range of AD8347 is 0.8-2.7GHz? So the doubler term,

2.88GHz, can never appear?

Has anyone tried any other components to realise this circuit?

Thanx in advance! kw

Reply to
john
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You don't need the sum frequency components for QPSK demodulation- so why would you want to "retrieve" them? And what are you using to "retrieve" them anyway?

Reply to
Fred Bloggs

Hi Fred

thanx fore replying!

I got the idea from this link:

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I can't get the waveform as shown in Figures 3 and 4 on the scope.I intend to pass this waveform thru a LPF (as suggested by the article) to recover the logic levels.

You mentioned that I don't need the sum frequency components (you meant the double freq component?) for demodulation, could you please explain the alternatives?

thanx again! kw

Reply to
john

Problem solved.

thanks to all that have responded! =)

Reply to
john

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