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!
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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
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