[USRP-users] N200 Factory Clock

Nowlan, Sean Sean.Nowlan at gtri.gatech.edu
Wed Jun 27 12:17:20 EDT 2012

>For compatibility with other TCXOs that may be installed and require a pullup, a pulldown, or a divider for enable and frequency control. On the FOX924B installed on the N210 those components are not required.

Can I assume the bias network is not needed on the N200 either, and that it has no effect on its operation? Also, is the latest revision of N200 still shipping with this same F924B part?

The reason I'm asking is because we observed quite a bit of drift using a freq counter driven by a Rubidium reference. I used N200 with RFX900 and a simple GNU Radio app (Const source --> USRP) to transmit a 900 MHz CW. We downmixed the 900 MHz CW to 100 MHz by using an 800 MHz CW from a signal generator running off the same Rubidium reference. The freq counter only goes up to 225 MHz. So we observed a range of values within 350 Hz on the 100 MHz CW. This is within spec for the F924B part, and I know there's a lot of freq synthesis, D/A conversion, and other stuff going on in the transmit chain, but what concerned us most was that the drift had high rates of change and near-discontinuities, rather than steady drift over a long period of time. Hence we were wondering whether the bias network was affecting the factory clock at all. A plot is attached. Thanks!

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