You can certainly open the squelch on your end, but at the events I was at recently, folks were able to reliably 'kerchunk' the repeater but not transmit audio - perhaps the transmitted audio just isn't often enough under bad conditions to open the repeater squelches, and that we can't change.
I have been musing on the possibility of getting around the canyon problem using longer wavelengths. This paper<http://images.rfdesign.com/files/4/0499WARNAG36.pdf> suggests that a Part 15 device could theoretically easily get 10 miles at 1705 kHz/100mW, at least during daylight. But it's very dependent on ground wave and noise floor, so probably it's no good for mobile stations for audio. But just maybe, with a low bandwidth digital mode, it would be enough for short texts, even if the antennas were suboptimal? I saw a video of a guy getting an urban 2 mile range with audio on medium wave AM using one of these kits <http://www.sstran.com/pages/AMT3000/overview.html>. I may get one just for experimentation purposes :) On Fri, May 23, 2014 at 8:34 PM, Guan Yang <[email protected]> wrote: > 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 >
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