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cyber-flyer

9600 FSK modem - success!

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I did it! 9600 bd FSK modem through audio channel of Felsweb TX/RX pair.

No special filters, no signal conditioning was neccessary. Just direct binary level input into audio channel.

This stripped down FSK modulation turned out to be much easier than AFSK because 0/1 output can be used directly without any need for sine waves.

Also bandwidth of Felsweb's audio is good enough to pass binary signal directly to laptop sound card. And yes, AGWPE reads it just fine.

The biggest problem was getting scrambling procedure right - I ended up using trial and error approach until hitting the right combination.

Mike, I hope ground station is in good shape - I may be able to test it very soon.

Regards,

Val.

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That is great news!

Is the signal just an analog copy of a simple TTL-like level RS-232 (no tones used)? What exactly is meant by "scrambling?"

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Amazing Cyber!

I did some more work on the ground station this week, APRS and also fixed the tracker. Now that I can use the TinyTrak it makes it easier to debug as well.

If you start using it, I will be much more motivated to put more time into it. ;-)

Cheers,

Mike

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Wow, Cyberflyer, that is an accomplishment. Congrats. I wonder how well the audio channel of other video Tx will cope with 9600 baud? What does your breadboard look like?

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Mr. RC-CAM, the modem is using TTL levels that are fed directly into audio input of Felsweb TX. Scrambling is additional data randomization process that is required for 9600 bd FSK operation - it is not present on 1200, 2400 bds AFSK.

Mike, can your ground station app read attitude data in the format that we agreed on? If yes, I'd like to start testing it.

I attach picture of development board with modem implemented on ATMega128. It sits next to RC-CAM's video swith board inside my system box.

Regards,

Val.

post-6-1081609251_thumb.jpg

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