Cannot choose TXA/TXB on BasicTX board

I can find RXA/RXB on BasicRX board in USRP source
However, where is TXA/TXB in USRP sink?
That doesn’t matter to transmit signal?

And one thing
Can I connect TX and RX directly with SMA-SMA cable?

When I use RFX400, someone advised me not to connect TX and RX directly
and to connect with some attenuator

But, some search after, I found that
people who connected Basic TX and RX directly with cable

2011/3/25 Songsong G. [email protected]

On Fri, 2011-03-25 at 18:02 +0900, Songsong G. wrote:

people who connected Basic TX and RX directly with cable
BasicRX and BasicTX, as well as LFRX and LFTX, are OK to connect
directly to each other, because there is no amplification of the signal
on these daughterboards. DO NOT DO THIS without attenuation on any other
Ettus R. daughterboards. Try 40dB to start.

–n