Bruce I'd suggest living with a +/- 2ppm oscillator design and have the modem capable of AFCing and pulling the oscillator against a table. You will striggle to keep it cheap searching for a 0.5pm oscillator- don't foget aging !
The receiver can of course build, over time, a lookup table of pulling v temp , also. Have a temperature lookup table that is written at manufacture time. Watch out for the TCXOs with SAWTOOTH (!) internal correction that leads to big jumps at times.... the receiver just needs , over aging of the oscillator, some means of tweaking its table. On 9/02/2015 11:47 AM, Bruce Perens wrote: > On 02/08/2015 02:40 PM, Gregory Maxwell wrote: >> Hopefully there will be room to add (or already included) a GPS receiver. > Hi Greg, > > We have a few approaches for precise frequency control. First, there is > a 10 MHz reference input with a signal conditioner chip. If you have a > small GPSDO, you can connect it there. The current sub-1PPM oscillator > is this one: > http://www.conwin.com/datasheets/tx/tx355.pdf > It doesn't have voltage control, and perhaps we should consider that. > We're out of connections on the instrumentation DAC, so we'd need to > change that, too. > > Another alternative is to steer the digital oscillator in the SDR. > > This really is a problem, because now that we have GMSK digital voice in > less than 1.2 kHz, our sub-1PPM oscillator can drift the width of an > entire simplex channel at our highest frequency. > > For a TDMA repeater, the repeater should be on GPSDO or Rubidium, and > the users should phase-lock to the repeater's frequency. > > Thanks > > Bruce > >> Beyond the very useful direct applications for positioning (APRS; >> automatic repeater directories; blind signal triangulation) and time, >> a GPS receiver would allow phase locking a VCTCXO to get good >> frequency accuracy for modes where this is required. >> ------------------------------------------------------------------------------ >> Dive into the World of Parallel Programming. The Go Parallel Website, >> sponsored by Intel and developed in partnership with Slashdot Media, >> is your hub for all things parallel software development, from weekly >> thought leadership blogs to news, videos, case studies, tutorials and >> more. Take a look and join the conversation now. >> http://goparallel.sourceforge.net/ >> _______________________________________________ Freetel-codec2 mailing >> list Freetel-codec2@lists.sourceforge.net >> https://lists.sourceforge.net/lists/listinfo/freetel-codec2 > > ------------------------------------------------------------------------------ > Dive into the World of Parallel Programming. The Go Parallel Website, > sponsored by Intel and developed in partnership with Slashdot Media, is your > hub for all things parallel software development, from weekly thought > leadership blogs to news, videos, case studies, tutorials and more. Take a > look and join the conversation now. http://goparallel.sourceforge.net/ > _______________________________________________ > Freetel-codec2 mailing list > Freetel-codec2@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/freetel-codec2 > -- - Glen English RF Communications and Electronics Engineer CORTEX RF & Pacific Media Technologies Pty Ltd ABN 40 075 532 008 PO Box 5231 Lyneham ACT 2602, Australia. au mobile : +61 (0)418 975077 ------------------------------------------------------------------------------ Dive into the World of Parallel Programming. The Go Parallel Website, sponsored by Intel and developed in partnership with Slashdot Media, is your hub for all things parallel software development, from weekly thought leadership blogs to news, videos, case studies, tutorials and more. Take a look and join the conversation now. http://goparallel.sourceforge.net/ _______________________________________________ Freetel-codec2 mailing list Freetel-codec2@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/freetel-codec2
