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[Discuss-gnuradio] Re: USRP MUX questions (Javs)

From: Anastasopoulos Achilleas
Subject: [Discuss-gnuradio] Re: USRP MUX questions (Javs)
Date: Sat, 23 Apr 2005 18:27:04 -0400 (EDT)

>> Are the connections from the daughterboards to the
>> ADC's
>> hardwired in the USRP the way it is shown in the
>> figure,
>> ie, RX-A to ADC-0, RX-B to ADC-1 and the IF output
>> of the
>> TV-RX to both ADC-2 and ADC-3 ?

>I think this is the default wiring:
>RxA (Jumper 19 )-ADC 0
>RxB (Jumper 18 )-ADC 1
>TvRx-Real - ADC 2
>TvRx-Imaginary-ADC 3

Is the output of the TVRX given in I and Q form, or
is it a signle bandpass signal at 5.57 MHz
(the final IF frequency of the tuner) ?
If it is the latter, then I would expect
that this signal is connected to both ADC 2 and ADC 3
for further down conversion and I/Q extraction.

>> According to usrp_wfm_gui.py the correct MUX seting
>> for listening to
>> FM is    0x f0 f0 f0 f2.
>>  To start with, why are we zeroing all Q
>> channels? If this is done then we should be getting
>> always a complex  number with zero imaginary part...

>Thats the intention. To receive only the real samples
>and provide a zero for all the imaginary samples.

This is not correct.
If we do that, then the phase of the received signal is always
zero, and thus it does not carry any information, which is exactly
what is supposed to happen in FM.
(Furthermore, this way we completely
ignore the imaginary part of the output of the TVRX (ADC 3 according to
your previous comment, which I believe it is wrong :-) )).


PS: I think I figured out the need for 4 DDC's.
This way with 2 Basic-RX modules we can sample
and process 4 independent input streams.

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