[Discuss-gnuradio] Can't transmit from USRP2

[Matigakis Emmanouil]

Hi,

I while ago we bought two USRP2. When they came we tested them with the usrp2_siggen and
usrp2_fft programs. Also we had two USRP1 and used USRP_oscope to see the waveforms produced
by USRP2. Everything seemed to work OK. Then we didn't do anything with the USRP2 for a while.
I few days ago I tried using them again and discovered I couldn't transmit or receive anything.
I saw in the mailing list that those who got an SD-Card labeled "9/22/08" must update their
firmware so I updated the firmware using the images from the site. Now I can receive(?) but
I can't transmit. I mean no signal is transmited from the USRP2'santenna because if it where I
would see it in usrp_oscope.  Samples however are send from the PC to USRP2 because the leds on
the Ethernet port light when I run a program like usrp2_siggen or something of my own.
Does anyone has any idea about what's wrong? How do I check if the transmit frequency has been
set OK? In another message it was mentioned that there is no PGA on USRP2. Then what does
set_gain() in a usrp2 sink or source?

I also noticed something about the received signal. First the noise variance seems to change when
there is a signal and when there is not. Is this normal? Is there some AGC circuit that causes this?
If so can I disable it from code. I haven't noticed anything similar in USRP1.

Thank you
Manolis