D-STAR, compared to an equivalent analog system (e.g. comparing standalone repeaters to FM repeaters, and simplex to simplex), offers both the low speed data services (for text, imaging, small file transfer, messaging), and increased range, compared to FM. All in all, it's a pretty compelling package, when you look at it objectively. All D-STAR needs now is:
-->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 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. -->Second, the fact that data is available at the same time is neat.if you need it. If you are actually running an EMCOMM net and sending valuable files back and forth simultaneously and seamlessly on the same channel, I'd love to see it. The truth is, the data stream supports voice and slow speed data. If the need is for me to key up for 1 minute and tell Net Control my story AND transmit a file to him simultaneously, it works cool. However, that is rarely the need. Well, tests done here have seen 120 mile and longer paths achieved on D-STAR, that were not possible on FM. The test repeater at that site would literally allow a QSO between stations over 200 miles apart. This is _demonstrated_ performance. Keep in mind that there are no such things as 10000' mountains down here (highest in the country is a little over 7200'), best you'll get is around half of that for a repeater site (and this particular mountain was probably nearer 3000'). On VHF, the D-STAR repeater on the other side of town is much easier to access than the 2m FM repeaters in the same area. Best range is (obviously) while stationary, but mobile performance here has been on a par with FM. --> 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? 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". I personally have heard good signals over paths I know I was not able to work on FM, without taking extreme measures, such as using a band that handled the terrain better (i.e. using 6m instead of 2m to get over a mountain in the way). Our experience here is that mobile coverage quite variable compared to FM (sometimes better, sometimes worse - suspect it's dependent on how much flutter there is), base station coverage significantly exceeds that of FM. Looks like we're in markedly different environments to get such different results. ==> 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 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 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. >-->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. 73 Daron N7HQR [Non-text portions of this message have been removed]
