Here is more info on how we could use the Navigation message of these old satellites for a rudimentary satellite Q-Tweet system. That is, you can send "Quarter-Tweets" for inclusion in the downlink... But only after you have scheduled a login and obtained (in the next downlink) your authorization code... See the drawing: http://aprs.org/transit/call-encoding.GIF
Using the scenario below: Bob, Wb4APR
-----Original Message----- On Behalf Of Robert Bruninga Sent: Thursday, August 26, 2010 8:39 AM Subject: [amsat-bb] Re: New Satellite Downlink?
Transits #23 and #25. object nos 19070 and 19419.
Here is a possible application based on the unique nature of the "navigation" message which is 26 lines of 6 words with each being 39 bits. But one word in each of the first 8 lines are changed every 2 minutes by inserting a new word and scrolling off the oldest one. We can use this for a list of callsigns.
We can get a callsign and extra 8 bit authorization ID into each of the 39 bit words. Then the rest of thos first 6 lines can be older callsigns and then the remaining 18 lines are available for what I call Quarter-Tweet messages of 35 bytes each. We will also reserve a few lines for special bulletins.
So here is how it would work.
- User initiates a login request via internet to
the command station.
- His call is added to the Login list on the
satellite plus an authorization byte
- As noted above, this list scrolls down and only
the last 48 are visible
- Next he has to tune in the downlink to see his
authorization byte.
- Now with his authorization byte, he can send a
Q-tweet via the internet.
- Which now shows up with 18 other Q-tweets in
the remaining 18 lines downlink
Your Qtweet can contain a call to another station and when he responds, you can count a QSO.
Something like that. The above idea lets everyone play, but requires that they can hear the satllite first (like any other satelite) before then can send an uplink (via the internet)
for
reception (downlink) via RF.
We will use a 5 bit code (like RTTY) but will replace the CR
and
LF with the "." and a CAPS shift. SO the 31 possible
characters
are a-z plus "." plus CAPS, FIGS and LTRS. This allows normal mixed case text...
Bob, WB4APR