James - thank you for taking the time to post this response. I'm sure it took a while to do, but this is the most comprehensive response I have seen yet.
I will reply back to some of your points. I would suggest that you go to http://aprs.fi and do a lookup on Bethel, Alaska. Don't look at the "Map", but in the upper right corner, select "satellite". I think that will give you a good idea of our area here in Bethel. I'll answer one of your questions first, and that is the reason for the 210 foot antenna height. Basically, on of the founding members of our local radio club is the chief engineer of our local (one of two) radio stations. The old analog television antenna has to come down, and because of FCC rules, it is easier to put "something" on the top of the tower and keep the height the same than it is to lower the tower. Therefore, we are going to put our local VHF and UHF repeater antennas at the top of the tower when the work is done. While the engineers are doing that work, we are going to have them put the antennas for the digipeater up there as well. Right now, our antennas are at 176 feet, and give us pretty good coverage. Remember, there are no other towns around us, so we need to get everything that we can out of the equipment we have available. Back to the placement of digipeaters. We anticipate that once the primary digipeater is in place on top of the radio tower that it will be our primary coverage device. What my concern is, and I think you are correct that it will just be a matter of playing with it, is whether or not mobile units placed on the periphery of town would be useful at all. Our town is very small (see the satellite image), so although I could see the potential of peripheral, fill in digipeaters helping out the HT signals reach the main tower / digipeater / IGate, I'm just not sure that they would be that beneficial. There are a few uses that we would like to use APRS for. Our radio club does quite a bit of work with the Yukon-Kuskokwim Health Corporation during emergency drills, mass dispensing exercises, pandemic drills, etc. We want to be able to use the bulletin board and other capabilities of the system to effectively move data during these exercises. Search and rescue is a major player, especially in the winter here, and we would like to be able to send messages to the search teams from a command post in town, as well as use it for position reporting. We also help support the Kuskokwim 300 dog sled race, and see position reporting as a big potential. As we are setting up our system, our biggest concern is with search and rescue. Although we are trying to increase licensure of that group, only a small portion of the SAR team has an amateur radio license. We are considering purchasing some trackers to place on snow machines for some of the non-licensed rescuers (we have some questions into the ARRL lawyers about some of this). Those that are licensed, we would like them to be able to use all the functionality of APRS, not just position reporting. The big issue here is safety. These SAR groups can go 40 - 60 miles out of town out onto the tundra to try to find someone who didn't make it in from a trip. In mid- winter, 4.5 hours of daylight is about all we get, so safety is a big consideration for this group. We want to be sure we can accomodate any operator in any way possible. That was part of the reason for chosing the Kenwood as a digipeater. We can utilize VHF and UHF, depending on the equipment a rescuer has as well as whatever antenna can get out the best given the conditions on a specific day. Also, the ability to update the group with areas that have been searched and other situational information from the command center is important to us. Finally, point well taken on the what happens when all the APRS stations are at the coffee shop on a Saturday morning, all digipeating the signals. Good illustration. To answer your last question, we have 50 not-so-well-equiped Hams. There is a core group of about 10 hams that have nice equipment, multi-band operations with decent antennas. There are about another 25 hams that have HT's with rubber duck antennas and no APRS capabilities. We then have some Hams that only use their radios on their boats and snow machines as an "emergency" device, primarily to get to the autopatch since cellular phone coverage is VERY limited and spotty here. I have to say that this environment is very challenging at times, but is an amateur radio heaven because of the possibilities of what we need vs. what we have. Thanks again for your comments and the time you put into your post. Spencer --- In [email protected], James Ewen <ve6...@...> wrote: > > On Tue, Aug 18, 2009 at 9:26 PM, spencerhamons<spencerham...@...> 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 >
