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

[Ian Holland]

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

Ian.



Hi Josh

Thanks for the advice. I tried the full range of low and high band
frequencies, in increments of 10 MHz with 2 different XCVR2450 boards.
This was done at least 4 times after power cycling for each card. I
noticed the following:

- For one of the XCVR cards, it repeatedly failed for all frequencies.
- For the other card, it intermittently failed for frequencies at the
lower and upper end of the low band, and at the higher end of the high
band. I tried several values of N_DIV_MIN_Q16, and expect with a really
large value (131 << 22), which seemed to fail for almost all
frequencies, and also seemed to cause the USRP2 to "freeze up" a few
times, I noticed negligible difference in the behaviour of this
daughtercard.
- For both XCVR2450s I noticed that sometimes after power cycling the
USRP2 either froze when I tried to run my test, or it was unable to be
found by my host PC in some cases.
- I tried (131 << 16) (i.e. original) value for N_DIV_MIN_Q16 and also
(131 << 19) on the card that failed for all frequencies, and that made
no difference.

I am not hugely concerned about the band-edge instability for the
working card (although of course it would be nice to get to the bottom
of that issue), but do you have any idea what could be wrong with the
2nd card, that fails for all frequencies?

Best Regards

Ian.


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

>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
custom 
>image. The file to modify is 
>http://gnuradio.org/redmine/repositories/entry/gnuradio/usrp2/firmware/
lib/>db_xcvr2450.c

>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,
>-Josh

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
noticed
> 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
being
> unable to lock.
>
> What can be done to make sure that it will lock? Is this likely to be
a
> hardware issue specific to our daughtercards, or is there something
else
> 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
the
>>> 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
future.
>>
>> 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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