[sat] Diskussion AX25 vs BPSK

[Robert Kiendl]

Hi zusammen,
 
Habe folgende interessante Konversation in der Amsat Liste mitbekommen.
Damit wäre BPSK eine Idee um Energie zusparen und somit mehr Daten runter zubekommen.
Einen BPSK Modulator hätte ich auch gefunden (https://wiki.mur.at/sat/TechCommunicationRadio), was meinen die Ap Leiter?
 
ciao lg Robert
------------------------------

Message: 8

Date: Tue, 7 Jun 2011 10:00:27 -0400

From: "Bob Bruninga" <bruninga at usna.edu>

Subject: [amsat-bb] Re: PSK v. APRS

To: "'Trevor .'" <m5aka at yahoo.co.uk>, <amsat-bb at amsat.org>

Message-ID: <059301cc251b$414f1bf0$c3ed53d0$@edu>

Content-Type: text/plain; charset="us-ascii"

> My pet hate is AX.25 1200bps FM [on] satellites...

> ...But the reason AX.25 1200bps FM is still used 

> for new satellites is because there's so much 

> infrastructure, TNC's, PC software etc, already 

> inplace, it's the easy option. 

Actually, there is another very important reason. Link budget.

With AX.25 one can have a 2W transmitter on a cubesat which has enough power

to hit an HT on the ground with a whip antenna. The same cubesat running

BPSK might be restricted to only 200mw.

The difference is the Duty Cycle. The AX.25 packet only lasts 1 second say

once every 10 seconds for an average power of 200mw. Which is the same

power as the continuous power of the BPSK (200 mw) which is all there is

available from the cubesat bus.

But the advantage of the AX.25 BURST mode is 10 TIMEs the RF power to the

user on the ground.

For FM mobile-to-mobile satellite communications on OMNI antennas, that is

why we use AX.25, to extend satellite links to mobiles.

There are of course other issues and BPSK does have better performance for

the SAME power, but as you say, there are not that many mobiles with SSB and

all the hardware necessary to auto-tune the radio to track the Doppler.

Bob, Wb4APR

　

　

------------------------------

Message: 9

Date: Tue, 7 Jun 2011 15:16:47 +0100 (BST)

From: "Trevor ." <m5aka at yahoo.co.uk>

Subject: [amsat-bb] Re: PSK v. APRS

To: amsat-bb at amsat.org, Bob Bruninga <bruninga at usna.edu>

Message-ID: <158528.63750.qm at web27204.mail.ukl.yahoo.com>

Content-Type: text/plain; charset=iso-8859-1

Hi Bob,

I accept what you are saying about burst mode but it's possible to develop a BPSK system that does burst mode too. 

A BPSK system with Forward Error Correction can offer a 16 dB advantage over AX.25 1200 FM. 

As you say there's loads of FM rigs out there so receiving AX.25 is simple and that's the reason everyone still uses it but for the future we should be looking to more efficient means of communication.

73 Trevor M5AKA

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mur.at/pipermail/sat/attachments/20110607/68ad63ba/attachment.html>