[USRP-users] Reliability of ref_locked sensor

mvw_forum at weymarn.net mvw_forum at weymarn.net
Fri Sep 7 11:15:40 EDT 2012


Nick,

Thanks, that is very useful information. The consequence is that we 
will have to implement an external detection circuit.

I am thinking along the lines of the schematic shown at the bottom of 
this page, followed by a comparator such as the MAX931:
http://ieee.ucsd.edu/wiki/tutorials/ac_coupled_single_supply_precision_rectifier_and_peak_detector

Do you think this will work with some tweaking of the components? Any 
other suggestion for a single supply of 3.3V?

Thanks,
Martin



On Fri, 24 Aug 2012 10:13:35 -0700, Nick Foster wrote:
> Martin,
>
> The AD9510 used in N210R4 (and R2) does sometimes indicate false 
> lock.
> We have been unable to convince it to indicate loss-of-lock reliably.
> In some cases switching from the external reference to the internal
> reference, and back again, alleviates the problem. I dont know why
> N210R2 would behave differently than R4 in this application.
>
> Automatic reference failover, unfortunately, is predicated on the 
> lock
> detect output working reliably -- which, as you have observed, is not
> always the case. I suppose future revisions or future products could
> possibly incorporate an external reference detection circuit.
>
> --n
>
> On Fri, Aug 24, 2012 at 9:15 AM,  wrote:
>
>> All,
>>
>> We are using an N200 R4 and supplying it with a 10MHz reference
>> clock signal of about 11dBm. Unfortunately it seems that a loss of
>> this signal is not always detected (ref_locked sensor remains
>> locked). In this case, while transmitting, our frequency jumps 20 to
>> 25kHz lower. This is rather fatal as we are planning to integrate a
>> USRP in a satellite test transmitter.
>>
>> Has anybody else noticed this behavior? Our N210 R2 seems to detect
>> the loss of the reference signal reliably.
>>
>> The N200 is a N200r4, hardware 2576, FW Version 12.3, FPGA Version
>> 10.
>>
>> On a side note, would it be possible to implement an automatic
>> switch to internal reference on loss of external reference? Maybe in
>> a future UHD release?
>>
>> Many thanks,
>> Martin v. Weymarn
>>
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>
>
>
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