Re: [Discuss-gnuradio] UHD USRP2 full duplex mystery solved

[Jason Abele]

>>> However, the WBX has enough internal leakage between tx and rx that we
>>> gave up on single-daughterboard full duplex.
>>>
>>
>> Just a heads up, you had not tried WBX without C1 installed on the
>> grand-daughterboard, or even without the grand-daughterboard at all,
>> just using J202 and J201 on the main WBX board, you might see if one
>> of those scenarios could meet your tx-rx isolation requirements.
>>

Sorry, missing and *if* in there ( ... Just a heads up, if you have not ... )

Basically, C1 allows for reception on the TX/RX antenna port, it
connects the two T/R switches.

However, if you are looking to do full-duplex, you will not be
receiving on the TX/RX port anyhow, just RX2.  So rather than having
an implicit leakage path through the T/R switches (RF switches rarely
give more than 20-30dB isolation, depending on frequency), you can
remove C1 on the grand-daughterboard and improve isolation at the
expense of not being able to receive on the TX/RX port.

If you want to go even further, you can remove the grand-daughterboard
entirely and install SMA connectors in J201 and J202.  You will also
need to move a capacitor to AC couple J201 and J202 to the circuit.

Jason