Re: [Discuss-gnuradio] Question about Basic TX/RX boards, the I, Q

[Eric Blossom]

On Tue, Apr 03, 2007 at 09:50:20AM -0400, address@hidden wrote:
> I can't get the output to the fm_tx_2_daughterbaords.py example to 
> work.  I am testing with 2 complex signals and on each signal, the 
> I channel is a sinusoid and the Q channel is a sinusoid of a 
> different frequency.  I have connected each of the 4 SMA 
> connectors from the 2 Basic TX daughterboards to a different 
> channel on an oscope.  I expect to see a sinusoid on each channel 
> but that is not the case.  I see some weird waveform on the 
> different channels on the oscope.  Originally I didn't think the 
> TX mux was set correct because the comments at the beginning of 
> the example says that it transmits SSB (USB) and that is not what 
> I'm looking for.  I want each of the 4 different waveforms (2 
> sines on the I's and 2 sines on the Q's, all with different 
> frequencies) to come out of the 4 SMA connectors.  Any help would 
> be greatly appreciated.
> 
> Thanks,
> Nick

Nick,

Without a serious amount of hacking you're not going to be able to get
4 unrelated signals out of 2 Basic Tx's, and if you could, you'd lose
the digital upconverters.

Each I/Q pair is sent through a DUC (in the AD9862) that computes the 
equivalent of

  OUT = IN * exp(jwt)

where IN is the I/Q input and OUT is the I/Q output, and w is the
freqency of the digital LO.

Given how the DUC works, you can't treat the I and Q as if they were
totally unrelated.  There's a reason they're called I and Q, not I1
and I2.

Eric