Need help with QPSK Demodulator

[john]

I've tried to realise the following circuit:

http://www.elecdesign.com/Files/29/3168/Figure_01.gif

from this article:
http://www.elecdesign.com/Articles/Index.cfm?AD=1&ArticleID=3168

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

 

[Fred Bloggs]

I've tried to realise the following circuit:

http://www.elecdesign.com/Files/29/3168/Figure_01.gif

from this article:
http://www.elecdesign.com/Articles/Index.cfm?AD=1&ArticleID=3168

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".

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?