For the VCO, how about a reactance modulator. They were very popular for the sweeping local oscillator in many a panadapter. Or perhaps one of the voice coil based wobbulators?
John WA4WDL ---- Bob Camp <[email protected]> wrote: > Hi > > I believe that if you dig into it, the correlator is either running quite > fast (in serial mode) or is pretty large (parallel processing). > > Since you know neither the code nor the doppler (no almanac) you are sweeping > both the frequency and the code. > > The VCO is a bit of a challenge (as mentioned earlier). Prior art was > basically a motor driven capacitor. Resolution / backlash / dead band are all > obvious issues. Not quite so obvious are dead spots in the capacitor it's > self and reversals in the tuning characteristic. It's the ratio of the tuning > range to the running accuracy that is the driver. > > Bob > > On Jun 24, 2013, at 8:40 PM, Jim Lux <[email protected]> wrote: > > > On 6/24/13 3:01 PM, Bob Camp wrote: > >> Hi > >> > >> I'm not so sure that "slow" would work. With all the sat's moving various > >> directions all the time, I suspect you need to do a solution fairly > >> quickly. If you don't the stale data messes up the solution. Also you need > >> the correlators to work fast enough to lock on to an essentially unknown > >> code before the sat is out of view. > >> > > The sliding correlator is pretty easy, and would lock up quite quickly. > > Basically, you need to have a vacuum tube PN generator to generate the > > correct Gold/Kasami code for the satellite in question (e.g. you need 32 of > > those generators). Each generator has a pair of 10 stage shift registers in > > it. I haven't looked in my copy of Millman and Taub, but I think you could > > probably build the shift register with 2*N devices (maybe N tubes, if you > > use dual triodes/pentodes, what have you). There might also be better > > choices for the tubes that have some form of latching behavior (thyratrons > > maybe..) > > > > You slide the correlator until it locks, and then it automatically also > > tracks the doppler of that S/V. I assume you'd use some sort of early/late > > tracker rather than a tau dither. I don't know what you'd use as the VCO, > > but there is probably some scheme (after all, FM transmitters existed > > before the invention of the Varactor solid state device) > > > > You can track the raw observables (code phase and Doppler) without needing > > to do a nav solution at all. And those observables don't change all that > > quickly (after all, the Doppler only changes a few kHz during many hours as > > the satellite goes from horizon to horizon). > > > > The trick is in how do you get the code phase into your nav algorithm. It's > > easy to get a pulse at 1 ms intervals when the code epoch comes by, but you > > really want to get a range estimate, and that means figuring out where you > > are in the bigger scheme of things. and, then getting that ingested into > > whatever computation scheme you're using. > > > > _______________________________________________ > > 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. _______________________________________________ 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.
