Using SmartSDR native Digital Modes with Satellites

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An interesting dilemma was discovered when setting up to use SmartSDR native FreeDV on the FO-29 satellite.

FO-29 as well as every Amateur satellite transponder actively used (except for AO-7 mode A) has an inverting transponder. You uplink in LSB (or DIGL) your downlink is USB (or DIGU)

Digital transmissions worked ok because transmitting in LSB inverted the uplinked signal, the transponder itself inverted again so the downlink signal orientation was correct.

With the SmartSDR FDV mode we have no way to invert the uplink signal so the resulting downlink signal after going through the inverting transponder will not have the correct orientation.

I suspect that DStar will have the same issue.

How 'bout a way to invert native digital modes either RX or TX?

Dave W0DHB
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W0DHB

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Posted 3 years ago

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Marc Lalonde

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HI 

was curious did the digital nature of the signal (100% duty cycle)  will not pose power issue to the satellite ?
battery on that bird was almost expired for long time now , and considering that battery going down to quick was cause of lost of A0-40( not permit to release latching relay) , think it may better to validate if this mode was OK  before try it 

Best 73!  Marc L. VE2OLM
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W0DHB

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Valid point Marc.

True that using digital modes with a high duty cycle through Satellite transponders is not the best idea.

Testis with FDV I have done have been low power and short in duration with FO-29, during the test I kept a close eye on the panadapter to make sure it was not adversely effecting other signals.

I used FDV and DStar as examples because they're currently the only Native SmartSDR digital modes. It's not going to be too long before we see native PSK, MFSK, etc modes with lesser duty cycles that are better suited for satellites start getting implemented.

The ability to invert Native digital signals not a high priority 'cause we can always use the current methods of modulating and demodulating digital mode signals.

73's Dave