On Tue, Aug 18, 2009 at 9:26 PM, spencerhamons<[email protected]> wrote:
> I have been reading through all the various information about Wide > Aliases on the board, and am a bit confused as to how best utilize > this where we are here in Alaska, and for the uses that we want to > utilize this for. A lot of the stuff we have been talking about here is well beyond where you want to be concerning yourself with at this point. The basics from your standpoint are pretty simple. 1) Define the area that you want to be able to track stations. 2) Figure out what you're going to use for tracker... ie low power HTs with bad antennas, or mobiles with good antennas 3) Determine how many digipeaters you are going to need to cover the area. (You'll need more digis if you are using poor trackers) 4) Put it all together and play. If you have one good high site that can see for a long distance, and it covers everywhere you want, then it's pretty easy. Put up a digi there, and get the trackers on the air. If you need more coverage, then you need to look at placing the digipeaters where they don't have serious coverage overlap. Good placement of the digipeaters is key to making a network that works well. Digis placed too close together can cause lots of noise, and degraded performance, whereas digis placed too far apart can leave gaps in coverage. It's a game you need to play. If you are out in the boonies where there is no one else around, then you don't have to worry about packets from neighboring areas flooding into your area using up local airtime, etc. > We are just now getting into APRS here, but we do not want to abuse the local > spectrum that we have. That's going to be a non-issue for you. A small close knit community can work well together to keep things working nicely. Problems arise where areas put too many digis too close together, or high digis that move traffic over hundreds of miles. There's only so much airtime available, and areas that have high density that overloads the channel invariably end up in the "shooting yourself in the foot" scenario. A user looks at the aprs.fi page, and sees that his track isn't showing every packet he sent. So, the usual solution is to boost the output power, because "The digis aren't hearing me!". That works for him until everyone else that he's now clobbering to be heard by the digis increase their power. Up goes the power again, and the others follow suit. Soon everyone is at 50 or 100 watts, and throughput is suffering. A single digipeater isolated from any other APRS network can easily handle about 50 itinerant stations with reasonable settings. If everyone wants to send a packet every 15 seconds 24 hours a day, that's probably not going to work, but if those that are in motion send a packet per minute, and back off when stopped, you can probably see reliable use. If you add a second digipeater to the network, your total throughput will drop because those packets are using more airtime. Remember that if you send a position report that uses up 1/2 a second of airtime, and ask for 1 hop on a digi, you now effectively use up 1 second of airtime. If you have 2 digipeaters, and ask for 2 hops, you'll now effectively use up 1 1/2 seconds of airtime for that one packet. Even if you can only hear 1 digipeater, that 1 1/2 seconds of time is used up. The local digipeater hears the initial packet in the first 1/2 second, sends the digipeat in the second 1/2, and then the local digipeater hears the remote digipeater digpeating the packet. A lot of people miss the fact that even though it sounds like the frequency in the local area is clear, according to the digipeater, the frequency is in use. If you think about areas where there are 3 or 4 digipeaters in range of the local digipeater, that local digipeater can be listening to a lot of activity on the surrounding digipeaters, but to the local user in the valley below, it sounds like the channel is empty. If they are sending low powered packets into the network, and not being heard, it is easy to make the assumption that there's a problem with the tracker, or possibly with the digipeater. In fact, it's just the fact that the digipeater can hear the surrounding digipeaters on the horizon much louder than the low powered tracker down below. > Right now, we have one "base" digipeater with 35 watts on a fairly > prominent hill. That base digipeater (mine) is IGated. This is a good start. > Otherwise, all other signals are coming from HT's or the occasional > mobile unit that someone has mounted. Of course, we want the HT's > to relay and the mobile to digipeat the signal. Okay, lets get terminology straight. RELAY can get confused... RELAY used to be an alias used by low powered mobiles when asking for a boost into the network from a home based station. I'm going to guess that you want the HTs to simply send position reports out into the network. It also sounds like you would like to have the higher powered mobiles to act as boosters to help the low powered trackers into the network. There are some things to deal with when trying to setup mobile fill-in stations. Normally the fill-in booster stations should be strategically located fixed stations. They would be located in areas where low powered trackers consistently can not get into the local digipeater, but that local digipeater can be heard in the area. If you can't hear the main digi in the area, it is probably better to look at adding another digipeater to cover the area. When you put these fill-in digipeaters into a mobile unit, they can work quite well when situated in appropriate areas. If however that mobile fill-in is parked in an area that is well covered by the main digipeater, it simply adds extra noise to the network. If we had intelligent fill-in digipeaters that would only digipeat a signal if the main digipeaters didn't respond, then it would be a great idea. Think about what happens when 4 or 5 mobile fill-in digipeaters end up in the parking lot of the local coffee shop on Saturday morning... > How would you suggest do this? Obviously the OT2 would do a bang up job of working as a tracker on these mobile vehicles, and acting as fill-in digipeaters at the same time as well. You could very well build the system you envision, and have it work for you... just be aware of the issues that you could end up facing, some of which I have touched on above. > To add some questions to the list, our local radio club is purchasing > a Kenwood D710, and our local radio station is allowing us to mount > our antennas for that unit at 210 feet. When that becomes available, >we will have much better coverage, but the HT's will still be a big > factor in our environment. What will the D710s role be in this system? Are you going to be using it as a digipeater? Just wondering why the 210 foot antenna height. I would suggest that the D710 is not a cost effective digipeater. There are much more economical options available, and ones that can fill the role of a digipeater better. The D710 gives you a good user interface for mobile operations. Connect it to an Avmap G5, or to a Nuvi 350 with GTRANS cable, and you get a great mobile mapping setup. > Any suggestions from you folks on how to best set this up? There are suggestions, but let's figure out what it is you are wanting to do first. > Again, we want to get our local group to use it (we have close to > 50 Hams in the area), but we do not want to abuse our spectrum. Are those 50 APRS equipped hams? 50 on an isolated network running reasonable rates when active should be quite acceptable. Abuse is a low priority worry at this time. James VE6SRV
