va3db, avatar
Reminding me how badly CSMA scales to packet radio, unless we could manage to get the /CD part in that is.
I wish there were some like minded hams near me so we could experiment with slotted Aloha. The early work with the Montreal protocol I did was all CSMA. Store and forward of course is a great use of a high tower as well and we had that on early Amateur Radio sats. (Larry Kayser)

HT @rdviii


@va3db @rdviii I fear that CSMA/CD on radio won't work.

The reason an FM relay has an input frequency and an output frequency is this: if you transmit, and would receive on the same frequency, then your own transmission would overpower your receiver frontend and would make it deaf.

Now assume you'd invent something that would solve this problem. Then you still have the problem that the signal of another participant on the same channel would be several orders magnitudes below your own transmission. Making the /CD part (collision detection) quite difficult.

And therefore FM repeaters use two frequencies. And packet radio uses CSMA, but not CSMA/CD.


@va3db @rdviii Oh, it occured to me that technially "FM repeater" isn't correct.

Or not showing the full picture.

Linear transponders which don't care for modulation (e.g. the one on ISS) also use different input / output frequencies. Hence their name, "transponder".

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