We might be able to use the L receiver as a backup, depending on the final digital transponder design, but it would only work well near apogee. The digital transponder needs to work over 75% of the orbit so that it's just as available as the U/V analog transponder. This mandates a phased array antenna with multiple receive paths. It's unlikely that all receivers in the array will fail so a backup receiver on another band isn't a big issue.
73,
John KD6OZH
----- Original Message ----- From: "Bill Ress" bill@hsmicrowave.com To: "John B. Stephensen" kd6ozh@comcast.net; "i8cvs" domenico.i8cvs@tin.it; jules@g0nzo.co.uk; "AMSAT-BB" amsat-bb@amsat.org Sent: Monday, September 11, 2006 06:47 UTC Subject: RE: L band
Hi John,
I have just re-read the Eaglepedia report of the San Diego meeting.
I must admit I continue to be shaken by Tom Clark's early statement about his views on the L-Band situation and then with the table called "Band Usage" which states L-Band usage (for digital) "Discarded due to possible L-band loss". I realize that this was referring to DIGITAL band
allocations
and that later a table called "preliminary power budget" includes 3 watts for a L-Band ANALOG receiver but I have been concerned that this position about digital L-Band is based on the unsubstantiated and unproven notion about the "government(s)" taking us off the air there.
John, I think engineering decisions should be based, as much as possible,
on
real facts and data - not a notion about the future.
Now another question. Why can't the L-band analog receiver (if it remains) be used for digital modulation (i.e. digital backup). Down to an IF frequency or modulation detection frequency it shouldn't care if the modulation is analog or digital. Have I missed something?
Regards and thanks for your patience and time responding to my posts.
Regards...Bill - N6GHz
-----Original Message----- From: John B. Stephensen [mailto:kd6ozh@comcast.net] Sent: Sunday, September 10, 2006 10:59 PM To: i8cvs; Bill Ress; jules@g0nzo.co.uk; AMSAT-BB Subject: L band
One thing may not be clear to all AMSAT members. There is still an L-band receiver in the Eagle requirements document for the analog transponder.
The
San Diego meeting recommendation was to move the digital transponder
uplink
from C to S. So far, no decision has been made to eliminate the L-band analog uplink.
The analog transponder has a U uplink so if L becomes inaccessible, it
still
works. The digital transponder has no secondary receiver so its uplink frequency is more critical.
73,
John KD6OZH
I would like the AMSAT decision makers to detail the reasoning for dropping the L-Band Uplink like a hot potato besides the "Galileo" excuse. As yet, I can't find it in Eagelpedia.
In view of Peter Blair's (G3LTF) paper (PLEAS SEE JULES LINK BELOW) I cannot see any rational for dismissing Eagle use of the L-Band
satellite
Uplink allocation. I don't thing using the statement that "we will
lose
our L-Band allocation" is indicative of the much appreciated
"science"
the team is bringing to the Eagle design process.