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[aprssig] Packet Radio Tone Generation

James Washer washer at trlp.com
Sat Dec 18 13:20:18 UTC 2004


I cannot claim to have written the code yet... but I've been thinking about it so here are my thoughts

2200 will NOT fit nicely at a zero crossing.

The two tones must remain "in phase"... i.e you cannot "jump" to the zero crossing point when you change tones.

Therefore, the best thing to do (IHMO) is to run two clocks, one, generating the correct ramp for the current tone, and another telling you when to change the first timer, and hence, the tone.

 - jim


On Sat, 18 Dec 2004 21:12:04 +1000
"Andrew Rich" <vk4tec at tech-software.net> wrote:

> Howdy,
> 
> Working the numbers for 1200 Baud packet generation using a PIC.
> 
> Does this look right ?
> 
> 1200 Baud = 1200 possible symbol changes per second
> 
> 1 Symbol change possible every 833 uS
> 
> Tones used are 1200 Hz and 2200 Hz
> 
> How then does 1200 and 2200 fit into the scheme ?
> 
> Does one cycle of 1200 Hz equate to enought for one symbol ?
> 
> 2200 does not seem to fit cleanily assuing zero crossing
> 
> Cheers Andy VK4TEC
> 
> 
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