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Re: [Discuss-gnuradio] Re: TX/RX simultaneously using one USRP board

From: Eric Blossom
Subject: Re: [Discuss-gnuradio] Re: TX/RX simultaneously using one USRP board
Date: Sun, 16 Apr 2006 14:23:16 -0700
User-agent: Mutt/1.5.9i

On Sun, Apr 16, 2006 at 03:28:51PM -0400, Dawei Shen wrote:
> Hi, Eric
> As far as know, Flex 400 only has a single subdevice.

single subdevice for Tx, single subdevice for Rx.

The Flex daughterboards look like two distinct pieces of h/w to the
s/w.  They have separate LO's, etc.

> How do you use one Flex400 daughter card for both transmission and
> reception at the same time? Do you mean I use only one antenna using
> the TX/RX port, or I use two antennas with one using Rx2 for
> reception and the other using TX/RX port for transmisson?

If you are transmitting and receiving full duplex (simultaneously),
you'll need to use TX/RX for transmit and RX2 for input (and you'll
need to be TXing and RXing at pretty widely separated frequencies,
and/or use a diplexer).  

The rx subdevice class has a method for selecting which antenna port
to use for reception:

    def select_rx_antenna(self, which_antenna):
        Specify which antenna port to use for reception.
        @param which_antenna: either 'TX/RX' or 'RX2'
        if which_antenna in (0, 'TX/RX'):
            self._u.write_io(self._which, 0,        RX2_RX1N)
        elif which_antenna in (1, 'RX2'):
            self._u.write_io(self._which, RX2_RX1N, RX2_RX1N)
            raise ValueError, "which_antenna must be either 'TX/RX' or 'RX2'"

If you're not transmitting and receiving at the same time, you can use
the single Tx/Rx port for both, along with Auto T/R mode

  self.subdev.set_auto_tr(True)  # must execute on both the Rx and Tx


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