On Fri, May 23, 2014, at 20:10, David Reeves wrote: > Ok, so is the reasoning here that some kind of direct FSK modulation will > suffer fewer of the propagation difficulties that we've seen with > reception > of voice/AFSK?
Yes; certainly on a per-baud basis. I've found that a lot of the time under bad propagation situations you can actually hear voices if you open the squelch. Something not mediated by the FM voice thing should be better. RFM23BP has a best case RX sensitivity of -120dBm, which is well below the noise floor at these frequencies. Of course we will have to test it. But even if propagation is just as terrible as FM voice, it will be easier to copy a digital transmission because we can do aggressive forward error correction and easily repeat transmissions many times. It's frustrating to be able to hear that there's *some* voice without understanding the words. Also talking to people is horrible even under ideal circumstances. > I'd assume this would be simplex only, which has in fact been by far the > most reliable over the few small-area (< 3 miles) urban nets I attended > recently. If we could get up to a 10 mile range somehow with some clever > digital processing, I'd think that would be very useful indeed for us > canyon-dwellers - do you think that might be possible? We could have digipeaters. That alone would help a lot. A 2m or 70cm FM voice repeater is a big hassle to move around and set up. With a $50 digipeater we could just plant them in various locations in the field and cross our fingers that they won't get stolen - and it won't be a huge deal if they are. _______________________________________________ Radio mailing list [email protected] https://list.hackmanhattan.com/listinfo/radio
