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Author Topic: CAMSAT CAS-4A & 4B Linear Transponder Payloads Launched  (Read 1186 times)
N8HM
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Posts: 157




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« on: June 15, 2017, 07:29:24 AM »

See http://www.amsat.org/?p=6080
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KC2NYU
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Posts: 171




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« Reply #1 on: June 16, 2017, 09:35:56 AM »

What does linear transponder mean to us rookies? Can we work with FM HTs? Or do u need ssb radios?

Paul
Kc2nyu
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WD4ELG
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Posts: 132




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« Reply #2 on: June 17, 2017, 12:21:17 PM »

https://forums.radioreference.com/satcom-space-satellite-monitoring-forum/202497-what-exactly-linear-transponders.html
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VE3WGO
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Posts: 111




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« Reply #3 on: June 18, 2017, 01:27:00 PM »

As the link in Paul's reply says, a Linear Transponder shares the power between users over its Receiver-Transmitter bandwidth, usually something like 20 or 30 kHz wide.  It is therefore best used for very low duty cycle and low average power modes like CW and SSB, in order to be able to share the satellite's transmitter power more evenly between all the users in the satellite's bandwidth, and could save the on-board batteries from being discharged quickly, or damaged, or both, when the satellite is not recharging in full sunlight. 

An FM signal on the other hand, is 100% duty cycle, ie continuously on at full power for the entire time while you talk, and therefore it would use a large amount of the satellite's DC and Tx RF power, leaving a lot less for the other signals in a linear transponder satellite's Rx-Tx bandwidth.  An FM-mode satellite on the other hand, is designed differently. It handles a single FM channel, ie only repeating one FM user at a time, and it can handle the power required for just that one FM signal.

Some satellites are designed specially to handle digital signals, which is a different design again, but that wasn't your original question.

So bottom line for proper results: use FM on an FM satellite, and use SSB and CW on the linear satellites.  See you on the hamsats!

73,
Ed VE3WGO
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