Temporary APRS digipeater

[AI8P]

Hello,

Yesterday my ARES group ran APRS on 3 buses at the Akron Marathon.   We were using simplex on 144.39 with a J-pole antenna at the Command Central.    I was thinking that there would be some digipeaters in this area which would repeat the APRS so that we could hear it at our location.   However, that didn't happen and we lost the signal for much of the course.

So,  for next year I definitely need some digipeating magic.   I'm wondering if it's possible to use a standard 2M repeater as a digipeater.    If I get permission to use someone's repeater for the APRS traffic, would that work?  I'm particularly worried about the repeater cutting off the beginning of the APRS signal.   Does anyone know typical TX delays needed to successfully get APRS thru a repeater, and can units like the TinyTrak 3/4 handle a long enough delay to make this feasible?

thanks for any help.

Dennis, AI8P

[WG8Z]

Hi Dennis
It's possible if the repeater contoller co-operates with you.
Some controllers/repeaters don't have a clean enough audio path or rolloff to digipeat a decode-able
burst.....TT3 manual states delay can be set up to 1.7 seconds,certainly enough unless the repeater has
anti-kechunk turned on.
Also some controllers DTMF tone blankers will activate upon receipt of a burst,not good either.
 We have used our FM Voice repeaters for legacy packet and WL2K,it works great,eliminates the hidden transmitter syndrome.....
For Events requiring tracking we set up a temporary digi or two to cover the course/area and move off 144.390.
This all but eliminates the packet collisions.....
73 Greg/WG8Z

[AI8P]

Greg,

What did you use for temporary digipeaters?  I have some TinyTrak4 that would work, but they don't have the elevation/coverage of the repeaters.   So I have a year to figure it out, but I think the height advantage of a repeater will make it worthwhile to tie up a voice repeater for this.

Dennis

[WA9AFM]

Dennis,

     What was the configuration of the APRS stations on the buses and how high was the J-Pole at your command node?

[AI8P]

The bus APRS varied from a Byonics All-In-One at 10 watts with an external antenna suction cupped to the window of the fiberglass bus, to a 5 watt HT transmitting from inside the bus.

The HT inside the bus didn't really work at all.   The AIO at 10 watts with external antenna was lost for most of the race.

At the GIC, we were in a upper loge at a baseball park and had a J-pole on an outside window.  The antenna was not above the stadium roof and I don't anticipate being allowed to put one up there, that's why I want to have a digipeater that can feed me the signals there.

Dennis

[WA9AFM]

The problem with the Byonics RTG is it has no receiver and thus, 'crashes' will cause packets to be lost.  Consider going with a rig that has receive capability with a TTIII. 

I wouldn't recommend using a voice repeater for APRS.  A portable APRS digipeater can be set up easily.  Several rigs (Kenwood D700 & 710 and Yaesu FT-350) have standalone digipeater capability.

For the Oklahoma City Memorial Marathon, we have seven vehicles on APRS.  We'll always loose a few position reports, but happens even with routine operations.

Tom Webb, WA9AFM/5
Chair, Public Safety Communications
Oklahoma City Memorial Marathon

[WG8Z]

Hello again Dennis
Several of the Guys have Kenwood D-700s..... I personally have some portable digi's.... v-8000 and ft-2600 with kpc-3's and 17ah gell cells strapped on.
73
Zed

[AI8P]

With All Due Respect, I think some of you are missing the point.

Most of the repeaters in this area do not cover the entire Marathon route.  Only a few repeaters in Prime locations can cover most of the Marathon route.

Putting up a temporary digipeater that can cover the route will not be "easy", and is not likely even possible.

I cannot get onto the towers to put up an antenna for this purpose.

That is the reason I am considering using an existing repeater.

Dennis

[K0JEG]

OK, here's two ideas:

1) Put a digipeater in one of the vans, with an external antenna and higher power. If grounding is a problem (you mentioned fiberglass), use a 1/2 wave antenna, like the Diamond NR770HA (I use it with great results). Use a gain antenna at the finish line (collinear, or a yagi if the race is in the same direction the whole time). The digi will have a better chance of picking up the other vans and passing them along, and will save a few bucks on the whole setup. And a better your setup on the vans the more likely you'll be picked up by other digipeaters.

2) Put a mobile IGate in one of the vans. Not an all-ham solution, but many smartphones will work like a hotspot or tether to get a PC on the Internet. Most of the IGate software out there is stable enough to work for a few hours without intervention. Set a path to another IGate that can be heard by the finish line if the owner has it set to gate traffic in both directions, or just have a hotspot at the finish line.

Everyone looks at the low Wattage beacons and think they'll do the job. They work great for some applications (like balloons), or if there are a lot of digipeaters around. If you're working without an infrastructure you need to do a lot more work. AFSK isn't very forgiving and voice repeaters aren't really designed to reliably pass it.

[K7RBW]

I agree with K0JEG...It just depends on which problem is easier to solve: receive the packets at the command post or receive the location information.

If you want to receive the packets, then you'd need digipeaters of one form or another placed where they'll get coverage AND beacons that are powerful enough to provide a reliable signal. My experience with low-powered beacons such as the AIO is that overall reception is pretty low when compared to more powerful mobile radio installations. My most recent mobile APRS rig used a 50-watt mobile rig, which helped, but even then there were dropouts. APRS packets are very short and very brittle (i.e. easily disrupted).

Strategic antenna placement for your digipeaters will be key, and using a freq that's not 144.39 would help reduce packet collisions to just your own radios, which is something you can work to minimize when you configure the beacons.

If you want to receive the information, you could place receivers and i-gates around the area to pick up the signals and upload them to the APRS servers. You can do this with non-APRS freq and  reduce the freq. congestion by not needing to repeat all the packets and not competing with all the other APRS traffic. The command post could just watch things in almost real-time by monitoring an APRS website. This would require some type of internet connection for each receiving station.

The problem with digipeaters is they use up the bandwidth that could be used by beacon stations.

The other thing to consider is whether you're asking too much of the APRS system. Are you expecting real-time, up-to-the minute location information of every unit, 100% of the time? That's probably asking too much without engineering a pretty robust system.

If you have reliable voice repeater coverage and volunteers, it might just be easier to do like you see in those old movies of British Bomber Command where you had a big map (real or virtual) and your field crew reports in with their location to the volunteers who update the map. I was playing with developing a web service that would do that on a Google map program. I had one page where you (i.e. your volunteers monitoring the voice frequencies) could input locations of your field assets (either numerically or graphically) and then another page would show those locations on the map for the command post view. That might be easier (and cheaper) to engineer than a 100% reliable APRS  system.

[AI8P]

Thanks to all for the many insightful suggestions.

I don't have internet at the Command Center for the Marathon and I hesitate to have someone in a van being connected to the Internet by cell phone for 6 hours and also don't want to do it with my cell at HQ either.   Additionally,  I don't want any delays as the Race people are constantly wanting to know exactly where the SAG bus is.  And a 50watt digipeater would not reach me from the Valley any better than the 10W beacon.

My experience with the 10W beacons with external antenna have been more favorable than some.   Last year I did an RF survey of the county using 10W APRS.   I have reviewed that data (should have thought of that sooner!) and concluded that:
1.  If I install a digipeater at the downtown EOC, it will cover all of the Marathon route except for the Valley
2.  An ARES member on the Western side of the city can cover most of the valley from his tower. 
3.  Time slotting should virtually eliminate packet collisions

I don't have weekend access to the EOC (no overtime for the government these days!) so I would have to install the digipeater there on Friday and just have it run all weekend - I would put it on an alternate freq so that it wasn't handling any traffic but mine.

Also, reception of the West side member (he has an APRS weather station) was intermittent during the Marathon, so I will need to get a somewhat better antenna at Race HQ to make sure I can get his signal.

I envision putting the EOC and member digipeaters on separate frequencies so I can switch between them as necessary at Race HQ.   I need to investigate the possibility of either switching the beacons between 2 frequencies (easily done with the AIO) or running a split frequency operation on one of the digipeaters

Thanks to you gentlemen I have been disabused of the notion of using a voice repeater, so I'm a step closer to a workable solution.   I do have a year to work out the details, but thanks much for your input.

Dennis

[K0JEG]

Additionally,  I don't want any delays as the Race people are constantly wanting to know exactly where the SAG bus is. 

Well, there's a big problem right there! When most people hear about APRS they tend to think it's like an ATC radar display or (even worse), a TV tech-crime drama. Setting expectations to a reasonable level will make a huge difference. 

My experience with the 10W beacons with external antenna have been more favorable than some.   Last year I did an RF survey of the county using 10W APRS.   I have reviewed that data (should have thought of that sooner!) and concluded that:
1.  If I install a digipeater at the downtown EOC, it will cover all of the Marathon route except for the Valley

That sounds like a great idea. And you might even be able to make the case that a permanent digi at that site could be a year-around benefit.

2.  An ARES member on the Western side of the city can cover most of the valley from his tower. 

Again, see if he/she would consider putting up a permanent digipeater. Having lived in an area where I had the only digipeater for about 60 miles (and in a lousy location) to an area with 3-4 good digipeaters, I can say that it doesn't take much to get coverage.

I envision putting the EOC and member digipeaters on separate frequencies so I can switch between them as necessary at Race HQ.

Running race updates shouldn't cause too much extra traffic on the network, I see them all the time in my area.

I need to investigate the possibility of either switching the beacons between 2 frequencies (easily done with the AIO) or running a split frequency operation on one of the digipeaters.

There was a plan on Bob Bruninga's site for building a 1200->9600 baud gateway using a D-700 and KPC-3 a while back. Look around, he's got a lot of good plans (although his budget seems to be higher than most).

It sounds like you're getting the right idea. You've got time, you know the route, so experiment. If 143.39MHz doesn't work well, try 70cm. 440MHz antennas are much smaller, so gain antennas are much easier to handle. But to me, it sounds like it won't take much for you to get better coverage with the 2 digis you spoke of, and there's not a ton of traffic in your area (or there'd be better coverage already). Also consider putting up PC based stations at food stations and for medical folks. That way they can send SMS-type alerts to the coordinators via the system in addition to the trackers. It gets a little more involved (mostly with keeping them powered up and manned), but messaging always seems to be forgotten in APRS world.

[N2ZNC]

You might want to look at Bob Brunigas website, especially at http://www.aprs.org/HAMsupport.html
Here he provides some info on a maryland trail, aprs project.
His site also has some info on setting up a digipeater. There are a couple of other info sites, that go into detail on setting up the kenwood d-710a. You could set up a mast with a good vhf antenna. Im experimenting with a Diamond x-500 a 40ft mast system, and a kenwood 710a to operate portable.

The portables transmit their position info on a separate freq offset with the digi listening on this freq. This reduces packet collisions. Im still learning and experimenting with this too.

good luck

George

[AF6OF]

 You can often send APRS data though a voice repeater, but many have CTCSS access, and many trackers are simple beasts, having no ability to send a CTCSS or DCS signal coincidentally with a transmission. You will probably have to enlongate your TXD settings to allow a voice repeater time to avoid clipping. It sounds like you need airborne digi support!

Allen AF6OF
VHS/Byonics

[W2RWJ]

I don't have internet at the Command Center for the Marathon and I hesitate to have someone in a van being connected to the Internet by cell phone for 6 hours and also don't want to do it with my cell at HQ either. 

Dennis,
You might want to borrow an Airlink Raven XE.  Most come with an ethernet port.  Here's a link:  http://www.sierrawireless.com/product/airlink/ravenx.aspx

They do work with Gateways and igates.   If you are buying on eBAY, ignore anything that says CPDP.   

Martin