Re: [Discuss-gnuradio] USRP1 Clock drift

[Nick Foster]

On Fri, 2011-01-07 at 10:01 +1100, Matt Robert wrote:
> Hi Guys,
> 
> I ran Kalibrate against my pair of USRP1's using GSM900 towers (around
> 940MHz) and found my first unit to me 5kHz off and the second was 13kHz off.
> 
> Is this within limits for the built in oscillator? I have been using
> them to transmit P25 frames around 435Mhz and found that my commercial
> P25 radios will not decode anything coming from the second USRP. The
> first USRP works OK. I have swapped around all daughterboards between
> both USRPs and the only common factor is the second USRP motherboard so
> I am sure its due to the clock in that unit.
> 

This is within spec. It doesn't tend to drift that much so if you
characterize how far it's off it'll stay reasonably constant (to a few
ppm) unless temperature changes drastically.

> Perhaps clocktamer or a secondhand GPSDO is needed for my Tx applications.

You will need an oscillator with a ~64MHz output to run the USRP1. There
is no 10MHz reference input on USRP1. I used a GPSDO and a homebrew PLL
based around an Si570 VCXO to keep mine synchronized, but it wasn't a
quick hack. Unfortunately there don't seem to be many 64MHz TCXOs in a
reasonable form factor out there.

--n

> 
> Cheers,
> Matt
> 
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