Need help with QPSK Demodulator

I've tried to realise the following circuit:
formatting link

from this article:
formatting link

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
Loading thread data ...
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:
formatting link
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

Site Timeline

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.