Re: [Discuss-gnuradio] WBX <70MHz

[John Orlando]

On Wed, Jun 2, 2010 at 4:29 PM, Matt Ettus <address@hidden> wrote:
> On 06/02/2010 02:06 PM, John Orlando wrote:
>>
>> On Wed, Jun 2, 2010 at 3:54 PM, Sharif Shaher<address@hidden>
>>  wrote:
>>>
>>> Hello,
>>>
>>> I am trying to tune the WBX to 60MHz, but everytime I do
>>> I get an error.  If I do it through usrp2_fft.py it says "Failed",
>>> if I do it through my c++ code, I get the error
>>> set_rx_center_freq(6e+07) failed.
>>
>> According to the driver, located at
>> gnuradio/usrp2/firmware/lib/db_wbxng.c, the minimum supported
>> frequency is 68.75 MHz, which makes sense since the ADF4350
>> synthesizer used on the WBX board only is spec'ed to run down to 137.5
>> MHz (and the quad demod chip on the WBX divides this in half
>> internally).
>>
>> That being said, these VCOs can typically be tuned lower in frequency
>> (or higher) than the min/max frequency specs, but you'll likely see
>> additional phase noise, and you'll be running outside the expected
>> operating range of the chip, which is generally not ideal.  But it can
>> be done.
>>
>
>
> No, we just tune to the lowest specified frequency for the VCO/PLL chip, and
> the rest of the tuning is done using the DDC/DUC.  Everything is used within
> specs.

Right...I wasn't implying that the driver for the WBX operates the
ADF4350 synthesizer outside of its spec'ed operating range, but I've
seen systems in the past that have taken this approach with
surprisingly good results (and of course lots of testing).  But when
things break, you're typically on your own.

The DDC/DUC approach is certainly cleaner, and does the job.

-- 
John Orlando
CEO/System Architect
Epiq Solutions
www.epiq-solutions.com