Using onboard GPS for position and time determination outside the GPS constellation altitudes in HEO was tested on AO-40 in the late 1990s.
https://ntrs.nasa.gov/api/citations/20030025378/downloads/20030025378.pdf
If the link fails, search for “AO-40 GPS Test” and it will bring up that paper and a few others. Unfortunately, the quality of the scan is less than ideal, but interesting reading anyway.
As Graham mentioned, a decade of development has resulted in chips which are more than good enough for amateur communications purposes. At least for the present. 😊
73,
Alan WA4SCA
From: Mark L. Hammond via AMSAT-BB [email protected] Sent: Saturday, September 14, 2024 21:53 To: Jon [email protected] Cc: [email protected]; amsat-bb [email protected] Subject: [AMSAT-BB] Re: AO-73 question
Hello, Jon.
We've been helping the MESAT1 team at Univ. of Maine. https://www.mainesat.org/mesat1/
GPS on this LEO satellite does indeed work. The idea of using it for frequency stability is neat :)
You can read https://iaru.amsat-uk.org/finished_detail.php?serialnum=822 and see this: "The MESAT1 spacecraft will also carry an L-band GlobalStar transmitter with a carrier frequency of 1616.25 MHz. This will be used along with the onboard GPS receiver, to provide back to our team, early mission TLEs"
73!
Mark L. Hammond [N8MH] AMSAT Director and Command Station
On Sat, Sep 14, 2024 at 8:13 PM Jon via AMSAT-BB <[email protected] mailto:[email protected] > wrote: Being in LEO orbits, can current day satellites use GPS disciplined oscillator (GPSDO)? They are still below the GEO orbit and should technically be able to receive GPS signals, but for the fact that they are moving very fast. Asking just out of curiosity.
73 de Jon, VU2JO
On Sat, Sep 14, 2024 at 10:30 PM graham shirville via AMSAT-BB <[email protected] mailto:[email protected] > wrote: Hi John,
I am not sure if you have received any other answer but…
AO73 has been operating in full time 24/7 transponder on mode for some time now.
The telemetry is also transmitted at low power at the same time on the nominal 145.935 MHz.
The nominal transponder frequencies remain unchanged: Uplink: 435.150 – 435.130 MHz LSB (Inverting) Downlink: 145.950 – 145.970 MHz USB
But these do drift a for Hz depending upon the on board temperature – back in the day, perhaps twelve years ago, the design of the oscillators was a compromise between stability and power consumption.
JO97, being a more recent design, does not have this “feature”.
73
Graham G3VZV
From: JOHN GEIGER via AMSAT-BB <[email protected] mailto:[email protected] > Sent: Friday, September 13, 2024 7:02 PM To: amsat-bb <[email protected] mailto:[email protected] > Subject: [AMSAT-BB] AO-73 question
Great to see that AO-73 has been QRV again. I seem to remember seeing somewhere that it has shifted frequency somewhat from the published frequencies. Is this correct? What are the current uplink and downlink passbands for it?
73 John AF5CC
Sent using {0}
-----------------------------------------------------------
Sent via AMSAT-BB(a)amsat.org http://amsat.org . AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Acceptable Use and Privacy Policies available at https://www.amsat.org/about-amsat/
View archives of this mailing list at https://mailman.amsat.org/hyperkitty/list/[email protected] To unsubscribe send an email to amsat-bb-leave(a)amsat.org http://amsat.org Manage all of your AMSAT-NA mailing list preferences at https://mailman.amsat.org