Hi Simple answer - adding gain will mess things up noise wise.
More detailed answer - The noise out of the GPS should be higher than the noise out of a reasonable TCXO out into the several seconds range. On a good TCXO it will be higher out into the 10's of seconds. On a very good one, you may get to the 100's of seconds. A lot will also depend on just how well the TCXO is shielded from drafts. Long time constants = low gain. Bob On Mar 15, 2010, at 6:06 PM, Joe McElvenney wrote: > Hi, > > I'm cobbling together a very basic PLL GPSDO with components I have to > hand which means I'm pushing my luck as far as the loop filter values > are concerned. > > These are - > > N = 1000 (10kHz ref from a Jupiter-T), > > Kv = 27Hz/V (10MHz Motorola VC-TCXO), > > Kp = 0.4V/rad from a 74HCT9046 type-II PD with charge-pump. > >> From these I've worked out some values graphically and with a couple of > apps I've found. They are an old DOS program by KD9JQ and a web one at - > http://www.aubraux.com/design/pll-design-tool.php > > The first tells me I need some gain between the loop-filter and the VCO, > the second (the third order active choice) seems (I think) to have the > capacitor values the wrong way round. > > My own efforts suggest I can get away with the values I've calculated > but with a lower loop bandwidth and longer lock-up time than I'd like. > The op-amp I'll be using for the filter, or extra DC gain for the VCO, > will be an OPA-703. > > How badly would sticking a gain block between the filter and the VCO > screw things up noise-wise (if at all)? Any thoughts on getting out of > the 'low resource' hole I've dug would also be much appreciated. BTW, > I'm not pushing any envelopes and my previous projects, with different > components, have worked out reasonably well > > > Cheers - Joe G3LLV > > _______________________________________________ > 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. > _______________________________________________ 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.
