Lux, Jim (337C) wrote: > These days, you might want to consider using the GaAs VCOs from Hittite, > rather than the DRO. DROs are SUCH a pain to build and tune, being a > mechanical resonator in a cavity. Everything you do seems to adversely > affect the DRO. The MMIC VCO is just a die (or a die in a package) and > it's > pretty much immune to external effects, since the resonator is built into > the oscillator. > > We built some prototypes at JPL using the VCO and a GaAs divider, and the > performance was better than DROs. > > If you were building a very narrow band PLL, where tunability of the DRO > isn't needed over a wide range, the DRO might be a good solution, but > still, > you have microphonics, etc. (we used to demonstrate the latter by hooking > up > the output to a spectrum analyzer that has a FM demodulator, and talking > to > the DRO)
We've used both. The DRO has much better open loop phase noise, and this synthesizer is for a single frequency, so the DRO only needs enough tuning to make up for drift. I was assuming the original poster would purchase a DRO. I agree that they are not something you want to build. We had no trouble with the ones we purchased from various vendors. BTW, the 5071A cesium frequency standard uses a DRO to help generate the 9192... MHz signal that excites the CBT, as explained in my FCS paper in the early 90's. I don't understand how you got worse phase noise with a DRO than a VCO, unless you used a narrow loop bandwidth for the DRO and a wide loop bandwidth for the VCO. We try to get the loop bandwidth up around 1 MHz for DRO's. The wide bandwidth also mitigates against microphonics. One thing we found was that you want to cover up the tuning screw hole so that microwaves don't go out of the hole and bounce around and go back inside. We had to put copper tape over it. Perhaps the original poster should start with a VCO and see if the phase noise is good enough, then go to a DRO if necessary. Rick Karlquist N6RK _______________________________________________ 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.
