At 01:50 AM 7/11/2009, you wrote: >-->First, there is literally no increased range. Do the math, look at the >required signal strength required at the receiver to reliably decode packets >and produce error free voice. Compare that value with your traditional >analog FM repeater receiver. Guess what, very much the same. No magic
Do some real world tests, side by side. I've seen an improvement in _useable_ range when switching from FM to D-STAR, and in some cases, repeater access on paths where FM is not viable (insufficient quieting to open the repeater's mute). The improvement for fixed stations is particularly significant. Mobile results vary (especially on 2 metres), due to the effects of multipath flutter, and can be better or worse than FM, depending on the local environment. I'm not talking theory here, but observations, both my own and those of others in areas I've known for 20 years (RF wise). >here, this is just RF. On the bench, side by side, you require a particular >measurable signal strength to open the receiver and produce reliable voice. >There is no magic in GMSK that provides recoverable audio where FM does not. >The difference is perception of noise. When the signals are compared on the >edge, at the same signal level, the FM gets noisy and the GMSK is quiet. >Push a bit farther and the FM gets very noisy, and the GMSK goes into R2D2 >and is unintelligible. True. The question is whether the FM gets too noisy or the GMSK goes R2D2 first. In many cases, it's the FM that becomes too difficult to use first. I'm not sure at what BER the R2D2 on D-STAR becomes a problem. I suspect it's somewhat higher than the BER (1%?) that the receiver sensitivity is specified at. The FEC that AMBE uses is very effective at producing readable audio under adverse conditions. >--> Awesome. Sounds like your analog repeaters need a tune up. I've been >able to demonstrate exactly the opposite in my terrain. So.who is right? Different terrain, no doubt. There are large areas of relatively flat plains in parts of the state. I'm in the middle of one of those plains (the basalt plains of Melbourne's west), and to the north of the mountains, the plains extend very far. That's probably one of the reasons. The same results have also been observed on simplex too. Does the radio "detune" itself when switching modes? ;) >Here is the deal, go pick up some GMRS handhelds at the store and look at >the 14 mile range they claim. Can they do it? You bet, line of site, no >interference, mountaintop to mountain top. Want to guess what they get in >town walking around between the buildings? It ain't 14 miles :-) We pushed >1200 DD ID-1 connectivity over 70 miles. Line of sight, hilltop to hilltop, >worked awesome. Same equipment, in town, not line of sight..less than one >mile. "demonstrated". Again, different terrain. I could take you out of town and get that 14 mile range. I'm sure it would be possible on the Hay plains (where an ant hill is the highest "mountain"). I can go the other way and get 50 or more miles out of those handhelds, if I went up a mountain. If you launched one onto a satellite, try 1000 miles. Range is relative to path, so your argument doesn't mean much, unless you're going to compare D-STAR and FM on the same path. You've had some poor results with D-STAR. Assuming all other things are equal (most equal is to use the same radios and switch modes), that suggests some environmental factor, and usually multipath is the culprit. >==> Again this begs the question about how well your analog stuff is >working. There is no magic in the GMSK that makes it perform better than Well, the analog performance is taken over a 20 year period, and a number of the repeaters had been overhauled in that time. >analog, except the fact that it is digital. Remember analog cell phones? >When it was on the edge, you got noise and static. Then they went digital. >Did the range increase because of the different mode? Nope, it's RF. What Apples and oranges. Power, cell size, etc. Here, we went analog, then GSM (still using it), then CDMA came along (now defunct), and now 3G. Each is to different to compare. >did change is the 'noise' went away and when you were on the fringe you got >garbled or no audio. The short answer.digital modulation (GMSK in this >case) is different than analog, but the 'transport' is still the same. It's a matter of which processing chain does the better job (16 kHz wide FM and human ears, or 6-7 kHz wide GMSK and AMBE with FEC). Throw in the usual collection of misaligned audio on the analog side (too soft, too loud, etc). All bets are off. :) There is an obvious 3dB advantage on the D-STAR side though, if you look at these figures. No magic, just bandwidth. > >-->Hmmm..you do get NOAA weather alerts over your D-Star repeater? We do on > >analog. You get site telemetry (battery voltage, VSWR, etc.) over your > >D-star? We do with analog. You have remote control of any of the site > >I don't see why D-STAR couldn't do those things. Someone has to >write the apps to do this, just like someone had to write the code >that allows your FM repeater to "speak" this telemetry. > > > >==> It could, it just doesn't, and may never do it. Believe me, I'm not >opposed to D-star, I have a VHF repeater, mobiles, portables and several >ID-1's we use for linking. What IS frustrating is the 'hype' that it is >somehow 'superior' to analog because it magically draws in signals that >can't be done with analog. Haven't been able to duplicate that on the bench >or in the field. Well, it's been demonstrated here by many, and the first evidence started coming in _before_ we had any repeaters, from people trying digital and analog side by side (there is a mode switch on the D-STAR radios). I've had good results, but mileage varies. 73 de VK3JED / VK3IRL http://vkradio.com
