At 9:56 PM -0800 12/5/07, Jeff Mock wrote: >I have a couple of Rb sources and went looking for spurs close to the >carrier. One was particularly surprising. First is a GPS disciplined >Rb oscillator from Berkeley Varitronics. I'm not a big fan of this box, >but that's another story. > >Here's plot of 500Hz around 10MHz, it looks like the 10MHz signal is AM >modulated with a 128Hz signal, the spurs are about -75dBc. I did the >plot twice, once during normal operation, and once with the GPS control >loop disabled from the front panel. The plots were identical. So, my >question is whether this modulation is part of the Efratom module or >introduced by the Berkeley Varitronics box? > > http://www.mock.com/test/rhinoii/am-128hz.png > >Here's a similar plot of an LPRO-101. This is just the module with a >semi-crappy power supply. There's a little 60Hz (+harmonics) that I >figure is power supply related leaking through the mixer. The 10MHz >signal is +8dBm, so the 60Hz spurs are at least 98db below the carrier, >much better than the previous graph and more like what I expected. > > http://www.mock.com/test/lpro-101/am60hz.png > >Does anyone know what's going on with the first box? > >jeff
Jeff, The modulation is how the device maintains lock. Read the manual for more info. Yours could have too high a modulation level. I don't know what the close-in spur level is supposed to be, but I could drag my FRS-N into the lab and measure it if you're interested. Just not this month since there's too much real work going on. -- --David Forbes, Tucson, AZ http://www.cathodecorner.com/ _______________________________________________ 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.
