802.11 Application Framework - Some questions about RF loopback mode

[zzzbengzzz]

Hello.

We (Our Lab.) are trying to utilize 802.11 Application Framework

by modifying some of functions in there.

Before we start, 

we test it without any changes in 802.11 Application Framework.

We choose 'RF loopback' mode and set 'power level' as 20 (dBm).

For testing, we do not connet any antennas.

See following pictures

 

As you can see,

without any antennas, 

It seems that there is no problem in communication between Rx port and Tx port.

(Weird result which we do not expect...)

We think that throughput, BLER, channel estimation, etc, all parameters are in normal range.

When we test it again with a lower 'power level' as 0 (dBm),

it seems to be normal operation, which exactly we expected when we do not use antennas. (corrupted constalletions and BLER equals one)

See following figure

Q1) Why this happen?

Q2) Is there any RF leakage from Tx port to Rx port even if we do not use any antennas?

Q3) Or this RF leakge problem happen indside USRP (in circuit level due to the some kind of shielding problem)

Thanks

Best regard

- Inkyu Bang