Crossposted to far too many groups, reply on s.e.d only The LPF is to remove the sum frequency RF+LO. Even if the mixer is specified for 800 to 2700MHz, the sum appears, is just doesn't see 50 Ohms anymore. Plus they don't specify amplitude and phase. How far down in amplitude were you able to measure ?
No, I didn't build it.
Rene
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?
I've tried to realise the following circuit:
from this article:
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
When the 8347 is specified for 800 to 2700MHz, this doesn't mean that nothing is coming out of it below 800 , nor above 2700, it just means the data, here the amplitude and phase is not specified. A DC coupled mixer always works down to DC, for example.
Is your scope that fast, that you can actually see the 1440 MHz ?
Rene
Thanx for your reply.
I trying to implement via this method:
at the moment, i've not implemented an LPF yet, can always use the scope to do that later.
I don't get what you mean by "Even if the mixer is specified for 800 to
2700MHz, the sum appears, is just doesn't see 50 Ohms anymore" can you please explain?I'm actually trying the get the signals as shown in figures 2 and 3 of the mention article.
thanx! kw
Hi Rene
thanx again for your prompt reply!
ok, noted.
yup, goes up to 4GHz.
Thanx! kw
Hi Fred
thanx fore replying!
I got the idea from this 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
Problem solved.
thanks to all that have responded! =)
but
is
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