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RE: [Discuss-gnuradio] Unable to tune Tx or Rx with XCVR2450 on USRP2

From: Ian Holland
Subject: RE: [Discuss-gnuradio] Unable to tune Tx or Rx with XCVR2450 on USRP2
Date: Thu, 4 Feb 2010 11:26:23 +1030

Hi Josh

I am now in a position to summarise what I have observed.

 - 1 of our 2 XCVR2450s works with both of our USRP2s.
 - The other XCVR2450 works with only one of our USRP2s (i.e., it fails
to lock over the full high band and low band on the second USRP2).

Do you have any idea what might be wrong? Has such behaviour ever been
previously observed? Also, can you please comment as to whether it is
likely that the other XCVR2450 will keep working with at least one



>Hi again Josh

>Since my below post this morning, the 2nd XCVR2450 card that had
repeatedly >failed this morning, is now working with the other USRP2,
though still >unable to tune reliably near band edges.

>I will probably try swapping the XCVR2450/USRP2 combination and see
whether >somehow one XCVR2450 has an affinity for one particular USRP2,
and won't >work on the other, but I can't really understand why that
should be the >case. Can you think of what might cause such a behaviour?

>For now, I was just glad that I could successfully transmit a 5 GHz
signal >from one USRP2's antenna and display the correct spectrum on the
receiving >USRP2.

>Best Regards


>Is it failing to lock at all different frequencies? and in the high
>and low band ranges? Do you have more than one XCVR board with this

>It could be possible that for this board, and the frequencies you have 
>chosen, the N divider value teeters on the border or locking/not 
>locking. You may want to modify the usrp2 firmware code and build
>image. The file to modify is 

>Add some printfs to the xcvr2450_set_freq function and try to raise the

>value of N_DIV_MIN_Q16 and see if you can get it to lock.

>I hope that helps,

On 02/01/2010 06:08 PM, Ian Holland wrote:
> Thanks Josh
> I can now confirm that it is definitely failing to lock. I have
> on some rare occasions that it actually does lock. However, as soon as
> the USRP2 is power-cycled it goes back to the default behaviour of
> unable to lock.
> What can be done to make sure that it will lock? Is this likely to be
> hardware issue specific to our daughtercards, or is there something
> we can do in software to get around it?
> Thanks
> Ian.
>> It could be failing to lock. You may want to watch the debug port on
> the
>> usrp2. If the lock detect is failing, it will print out on the serial
>> console. attach a 3.3v level serial port
> On 01/28/2010 10:09 PM, Ian Holland wrote:
>> Hi Josh
>>> The xcvr has a high band and a low band, which means there is a gap
> in
>>> the tunable frequency range for the xcvr. Therefore, the
>>> "auto-calculated mid-point frequency" is an invalid frequency for
>>> xcvr. Pick a frequency in the high band or low band range:
>>> #define LB_FREQ_MIN U2_DOUBLE_TO_FXPT_FREQ(2.3e9)
>>> #define LB_FREQ_MAX U2_DOUBLE_TO_FXPT_FREQ(2.6e9)
>>> #define HB_FREQ_MIN U2_DOUBLE_TO_FXPT_FREQ(4.8e9)
>>> #define HB_FREQ_MAX U2_DOUBLE_TO_FXPT_FREQ(6.1e9)
>> Thanks - I will keep that in mind when using usrp_siggen.py in
>> However, I have tried 2.4G with the source code from my original post
>> (relevant code snippet for Tx tuning just below this paragraph, for
>> which successTx is 0 and all frequency properties in TxTuneResult are
>> 0), and also with usrp2_fft.py -f 2.4G, after burning the latest
> images.
>> I still face the same problem that neither the Tx nor the Rx will
> tune.
>> /* try tuning Tx to a test frequency */
>> double Fc = 2400000000.0;
>> usrp2::tune_result TxTuneResult;
>> bool successTx = device->set_tx_center_freq(Fc,&TxTuneResult);

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