30 dBm is 1W, right?
On Fri, May 23, 2014 at 9:13 PM, David Reeves <[email protected]> wrote: > 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 >> > > > _______________________________________________ > Radio mailing list [email protected] > https://list.hackmanhattan.com/listinfo/radio >
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