Dear time nuts, Background: I have built a GPS receiver based around the SE4120L front end IC [1]. I used a KT3225 TCXO [2] at 16.3676MHz driving the front end through a 10nF series capacitor as in the example circuit in [1]. Inside the front end, this oscillator is multiplied up to form a local oscillator at 1571.2896 MHz. The 16.3676MHz signal is also divided to form a 4.0919MHz sampling clock. Digital I and Q samples then go to a DSP where the GPS signal processing is done in software. My receiver works nicely, getting it online was a boatload of fun and I'm hoping to make it available soon along with open-source software as a GPS experimenter's kit.
Problem: I'd like to clock multiple receivers from a single 16.3676MHz oscillator, in order to combine measurements from multiple antennas. The clocks must be at the same frequency, i.e. from the same source, but it is not necessary that they have any particular phase relationship as phase offsets are removed in the navigation processing. What sort of distribution amplifier should I use to split the output of one TCXO into four front ends? Do I need some kind of impedance matching network? How would I go about designing that? This sort of analog/RF design is unfamiliar territory for me, though I'd like to learn. The TCXO advertises a minimum output level of 0.8Vpp into (10kohm in parallel with 10pF). The front end requires a minimum oscillator drive level of 0.2Vpp. The front end datasheet lists "recommended crystal parameters" including a load capacitance of 10pF (typ), although I don't know whether or not that refers to the front end input capacitance. My guess is that phase noise performance is not particularly crucial, at least by time-nuts standards. I guess it would be nice if the amplifier didn't make the phase noise "significantly" worse than it already is from the cheap TCXO. Many thanks, Henry Hallam [1] http://www.sige.com/support/download-form.html?dl=DST-00059_SE4120L_Datasheet_Rev_3p5_CYW_May-26-2009.pdf [2] http://global.kyocera.com/prdct/electro/pdf/tcxo/172_e.pdf _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
