Re: [Discuss-gnuradio] [USRP-users] questions about calibration examples in UHD utility

[gang li]

Hi, Mike,
Thanks very much for your reply. I also searched  online about the
usrp calibration. I found a post and some information:

"During cal, the TX is switched away from the TX antenna into the
"closed" switch port, where it leaks into the RX which is listening to
the TX/RX antenna. So termination on RX2 should have no effect as that
port is already unused in calibration."

Here is the link:
http://lists.ettus.com/pipermail/usrp-users_lists.ettus.com/2012-April/004028.html.

I am a little confused. Since calibration uses full duplex, why is
there no direct connection between RX2 and TX/RX? I thought they are
connected inside the usrp during calibration.

Best,
Gang


On Mon, Jan 28, 2013 at 4:08 PM, Mike Jameson <address@hidden> wrote:
> Hi,
>
> Calibration uses full duplex and should only be done without anything
> plugged into the 'tx/rx' or 'rx2' ports. There is no direct connection, just
> measurement of the residual rf escaping.
>
> Mike
> M0MIK
>
> On 28 Jan 2013 20:17, "gang li" <address@hidden> wrote:
>>
>> Hi, guys,
>>
>> I am reading the codes for uhd_cal_rx_iq_balance.cpp.
>> When doing calibration by setting the RX and TX antenna as "CAL", is
>> the signal from TX directly switched to RX?
>> And I noticed that in the function set_optimum_defaults(), the tx_gain
>> is 0 but the rx_gain is 25! Is that too high? I heard that when
>> directly connecting TX and RX, we should use attenuators. So why does
>> it set 25 rx_gain? Thanks.
>>
>> Best,
>> Gang
>>
>> _______________________________________________
>> USRP-users mailing list
>> address@hidden
>> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com