Re: [Discuss-gnuradio] IQ imbalance...

[Jeff Brower]

Per-

> I also have a xcvr2450 that won't lock sometimes. This is at 2.4GHz.
>
> Also an issue about IQ imbalance:
>
> I am measuring IQ imbalance. The values are generally quite good.
> However, one thing I don't understand is that the mirror frequency
> doesn't turn up on exactely "-f" but a few Hertz off. I don't get this.
> Are we sure that the down-conversion on the FPGA is completely turned off ?

What size FFT are you using to see the mirror freq?  What is the bandwidth of 
the data into the FFT?  From this you
could calculate Hz/bin and see if that helps to explain the offset.

-Jeff

> Ian Holland wrote:
>> Hi Matt
>>
>>
>>> Yes, -9 dBm is safe.
>>>
>>
>> Glad to know it was all safe re input levels.
>>
>>
>>> I have not seen the problem locking without trying a lower frequency.
>>> What if you try 5 GHz twice in a row?
>>>
>>
>> The problem with the not locking to 5G is very intermittent. A few times
>> when it did occur, I tried your suggestion of trying 5G a second time:
>>
>> 2 out of 3 times, it locked the second time. The other time, it did not,
>> but then trying 2.35G followed by 5G did then work.
>>
>> Regarding the other intermittent issue that appeared as IQ imbalance, I
>> have swapped the USRP2/XCVR2450 pair used for transmit with the receive
>> one, and haven't observed the issue since. It may still occasionally
>> occur for the first pair, but this is a workaround for me. I am still
>> confused as to why it occurred to begin with.
>>
>> Best Regards
>>
>> Ian.