APRS high school math

I can not believe that I forgot all those formulae I knew so good in high school

Those flying with APRS and still remembering calculus please help.


Question is - Will twenty 5W APRS transmitters reliably work in a radius approximately 100 km from the base station at altitude of 300 meters? No repeaters, flat surface no hills.

Somebody very interested just asked me the question and I have a brain lock Mathematicians, students, rocket scientists please help...

Vladyspassky said:

I can not believe that I forgot all those formulae I knew so good in high school

Those flying with APRS and still remembering calculus please help.


Question is - Will twenty 5W APRS transmitters reliably work in a radius approximately 100 km from the base station at altitude of 300 meters? No repeaters, flat surface no hills.

Somebody very interested just asked me the question and I have a brain lock Mathematicians, students, rocket scientists please help...

Click to expand...

Vlad, I can't provide a mathmatical answer, but based on my experience with a tracker in the plane I think you have a good chance of satisfactory coverage.

However, there are many variables that prevent a definitive answer; somem of which are, antenna used, the meaning of "reliable", the quality of the iGate receiver, and whether or not the frequency is clean in the area.

Good luck with the project, whatever it is!

My trusty ARRL handbook says the distance to the radio horizon (on the ground!) under average conditions can be estomated by:

d = sqrt(2h)

where d is the distance in miles (probably statute miles) and,
h is the height above the average terrain in feet.

Sensitivity issues aside, according to this and if my calcs are correct 300m elevation gives an horizon of 71km if the station is on the ground. At 100km you would need to be above about 162' AGL to hit the base station.

Doug
RV6
VK2GCV

Vlad,

I'd be very interested in your test results. I've been trying to evaluate a few different tracking methods to see what might work best to display multiple tracks during SARL races (such as the iPhone Tracklog app, Skycharts, SPOT, etc.)

APRS seems to provide the most reliable tracks under the widest variety of conditions, but until recently it appeared to be limited to one track per webpage displayed. I just saw the beta being tested to display 20 APRS tracks simultaneously, and figure that may be what you are looking at as well.

I'm going to try to run a Tracklog Group Track during the Rocket 100 race on 11/21 (if there are multiple iPhone users among the racers), and if there are multiple APRSers in the race, I'll also try to test that APRS beta. Your description of range and altitude is very similar to the parameters I'm looking at as well.

Please let me (us) know if you have any successes in testing, and I'll do the same (if you'd like to collaborate a bit, I'm all in!)

Cheers,
Bob

aprs

I have been able to use the show all link on the right side panel of aprs.fi site to show all tracks or targets selected in the prefrences for the site . would that be of any help for what you want to do .

Gary Holderbein

ki6piy

aprs at taylor race

Bob,
If the weather gods are good to us, a few of us will be coming down from Canada to the Taylor race. I will have a portable aprs unit in the plane with me, and will have it on for the race as well. Hopefully a few more will have one there as well to test the tracks for you.

rvmills said:

Vlad,

I'd be very interested in your test results. I've been trying to evaluate a few different tracking methods to see what might work best to display multiple tracks during SARL races (such as the iPhone Tracklog app, Skycharts, SPOT, etc.)

APRS seems to provide the most reliable tracks under the widest variety of conditions, but until recently it appeared to be limited to one track per webpage displayed. I just saw the beta being tested to display 20 APRS tracks simultaneously, and figure that may be what you are looking at as well.

I'm going to try to run a Tracklog Group Track during the Rocket 100 race on 11/21 (if there are multiple iPhone users among the racers), and if there are multiple APRSers in the race, I'll also try to test that APRS beta. Your description of range and altitude is very similar to the parameters I'm looking at as well.

Please let me (us) know if you have any successes in testing, and I'll do the same (if you'd like to collaborate a bit, I'm all in!)

Cheers,
Bob

Click to expand...

Vlad and Bob,

After thinking about your projects for a bit, I think it might be good to modify the tracker configs from what we usually use for aviation tracking.

My concern is that if SmartBeaconing is used on all the trackers, when several planes begin turning at the same time, you will see the mother of all frequency traffic jams! This will result in packet collisions at aprs.fi and a whole bunch of packets will be discarded.

I don't know the particulars of what type of tracking you are needing for the races. If fine resolution of the aircraft are not needed in turns, you will still get good tracking without SmartBeaconing. Another feature of the tracker config software is the ability to use a GPS time offset. Each tracker could have a different offset so collisions could be minimized.

We'll be looking forward to hearing how the trackers perform during the races.

Range Calculations

The actual range will generally be shorter than the maximum predicted range based purely on antenna height and power as the factors in determining the radio horizon. To calculate the actual range, you need to know the transmission path losses, antenna gain (on both sides) and the receiver sensitivity. My guess is that for trackers at an altitude of 300 meters, and a reasonably good receive antenna, you will be on the border of establishing a solid link. Packet collisions are another story. You have probably heard anecdotal stories of people hitting digipeaters at 1000 foot altitudes at ranges of several hundred miles, even with lower power transmitters. Air to ground is much more forgiving then radio waves carried over the water or ground. I would test the coverage before relying on it for an actual operation though!

Allen
VHS
AF60F

Gents,

Just wanted to catch up and reply to a couple posts, so here goes:

Vlad, replied to your PM, and sent the link to the blog that discusses multiple tracks on APRS (re-pasted here):

http://oh7lzb.blogspot.com/2009/10/beta-test-multiple-target-tracking-on.html

That blog has a link to the beta APRS.FI, which is here:

http://beta.aprs.fi/

Good luck to your friends in their testing!

Sam, I do understand what you are saying...multiple turning aircraft with smart beaconing on = potential igate overload. During a race, the aircraft are launched about 30 seconds apart. so there aren't usually multiple aircraft at one turn at the same time. However, its still a small geo area, and there could be several airplanes at various turn points in the race, all still sending packets at rapid intervals. So smart-beaconing off may be a very good way to go. Rapid updates would enhance the viewing for race fans though, so would you have a recommended minimum packet interval to avoid packet collisions (for instance, would 30 seconds be too much data traffic?)

As for the GPS time offset, I'll have to get smarter on that (I'll have to confess, I still don't have my HAM or my APRS...keeps getting slid to the right by airplane repair work or job-work. I've talked to Allen about the gear, looked at the forum for the gouge you've provided...now just gotta get the tests, study up and then go for it. Might be able to put the unit on my XMAS list!) Once I get it and really tinker with the settings, I know I'll understand more what you are talking about.

In the meantime, I'll try to work with the racers at Taylor to try Smart Beaconing off, and see what we can do. I'll post a list of racers with APRS running in Taylor on the 21st, and maybe a few of you can tune in and let us know how it looks! Gary, will work with you and the others to get things set up!

Thanks much!
Cheers,
Bob

rvmills said:

Sam, I do understand what you are saying...multiple turning aircraft with smart beaconing on = potential igate overload. During a race, the aircraft are launched about 30 seconds apart. so there aren't usually multiple aircraft at one turn at the same time. However, its still a small geo area, and there could be several airplanes at various turn points in the race, all still sending packets at rapid intervals. So smart-beaconing off may be a very good way to go. Rapid updates would enhance the viewing for race fans though, so would you have a recommended minimum packet interval to avoid packet collisions (for instance, would 30 seconds be too much data traffic?)

Click to expand...

Good questions, Bob, and I suspect we are too close the bleeding edge of aprs race tracking to know the best answer. Thirty seconds with no SmartBeaconing would probably be a good starting point, and mods can be made after a race or two if necessary.

As for the GPS time offset, I'll have to get smarter on that (I'll have to confess, I still don't have my HAM or my APRS...keeps getting slid to the right by airplane repair work or job-work. I've talked to Allen about the gear, looked at the forum for the gouge you've provided...now just gotta get the tests, study up and then go for it. Might be able to put the unit on my XMAS list!) Once I get it and really tinker with the settings, I know I'll understand more what you are talking about.

Click to expand...

In a nutshell, the tracker pulls time from the GPS so all trackers should be pretty much in sync. Take a look at the field on the right side of the config labeled "time slotting":



Each tracker could be set with a different offset from the top of the minute. Since SmartBeaconing would be disabled, each tracker's beacons should be sent at its individual offset. Guess you would divide 60 seconds by the number of trackers to find the offset.

Most likely some packet collisions would still occur at the iGAte but maybe this would minimize the problems.

In the meantime, I'll try to work with the racers at Taylor to try Smart Beaconing off, and see what we can do. I'll post a list of racers with APRS running in Taylor on the 21st, and maybe a few of you can tune in and let us know how it looks! Gary, will work with you and the others to get things set up!

Thanks much!
Cheers,
Bob

Click to expand...

We look forward to seeing how this works. Yep, send Santa a note!

Packet collisions with APRS

Since this gentleman is setting up his own I-gate, he could use more than one frequency off the APRS National channel, and just use multiple receivers at the base station end. This would help his throughput tremendously.

Allen
VHS
AF60F

VHS said:

Since this gentleman is setting up his own I-gate, he could use more than one frequency off the APRS National channel, and just use multiple receivers at the base station end. This would help his throughput tremendously.

Allen
VHS
AF60F

Click to expand...

Allen, I thought about that option but didn't suggest it because I didn't know how complicated they wanted to make their system. Having only 2-3 trackers on a freq should really clean things up. Also don't know how many freq agile trackers they have.

But that may be the ultimate solution.

Sam and Allen,

Copy all, and as I work with APRS-equipped racers for the Rocket 100, I'll ask that they turn Smart Beaconing off, and once I know how many have APRS on board, I can see if I can assign appropriate time offsets for them each to use.

I'm going to go on the SARL site and see if I can set up a group of APRS tracking racers, and will post call signs here before the race. I'm also going to see how many racers have iPhones and set up Tracklog group tracking for the race if there are others besides me with Tracklog. Will post that info before the race as well. It'll be interesting to compare the two, if I can gather enough participants in each category.

As far as the igate that you mentioned, I think you are talking about Vlad's friends setting one up, but not sure. They are in a galaxy, far, far away, so not sure if or how the freqency management will be an issue for them. With respect to SARL races, it does bring up an interesting concept...that of a mobile igate, or one that could be moved from race to race and set up at the start/finish airport. Hmmm...something to think about and refine after some initial testing. If we choose that route, I'll be back to pick your brains on multiple frequency usage as you guys are discussing.

Thanks much, and I'll shoot back some info on race tracking for next weekend after I set it up.

Cheers,
Bob

Bob: We have a similar problem I'm trying to work out with our late spring race the "Race to Ridgeland". I'm trying to get the local ham guys interested; perhaps they could establish a mobile iGate in the middle of the course and transmit through the internet from there, accessible to "race control" at the start/finish line. I still haven't figured out how to get my hands on 20-30 sets of APRS transmitters to issue to the racers.

If that won't work, I would really appreciate hearing what other ideas there may be out there. We fly approx 125 miles in our race with some mildly complex turns at the airports we use for turn points; and yes, we occasionally get those who don't make the correct turns, but I can't afford to have spotters at every location. It would be great to be able to ensure that all contestants actually fly to every turn point without the overhead of a bunch of volunteers having to drive an hour or so each way to get to the turn points.

Please keep us informed on your progress!

Lee...

rvmills said:

As far as the igate that you mentioned, I think you are talking about Vlad's friends setting one up, but not sure. They are in a galaxy, far, far away, so not sure if or how the freqency management will be an issue for them. With respect to SARL races, it does bring up an interesting concept...that of a mobile igate, or one that could be moved from race to race and set up at the start/finish airport. Hmmm...something to think about and refine after some initial testing. If we choose that route, I'll be back to pick your brains on multiple frequency usage as you guys are discussing.

Cheers,
Bob

Click to expand...

Bob, you definitely need to think in terms of a mobile iGate if there is not good iGate population near the race. All you would need is some simple equipment and broadband internet access. No license required to operate an iGate.

http://www.vansairforce.com/community/showthread.php?t=30180

logansc said:

Bob: We have a similar problem I'm trying to work out with our late spring race the "Race to Ridgeland"...snip...Please keep us informed on your progress!

Lee...

Click to expand...

Sam Buchanan said:

Bob, you definitely need to think in terms of a mobile iGate if there is not good iGate population near the race. All you would need is some simple equipment and broadband internet access. No license required to operate an iGate.

http://www.vansairforce.com/community/showthread.php?t=30180

Click to expand...

Lee, will keep you up on the progress, and will post something later this week about how many APRS-equipped racers we'll have in Taylor this weekend (so far the response has been slow, but I may not have good info till the night before). I'll start a separate thread before I blast off for Taylor, probably in the test or general section (since it will have iPhone and SPOT info in it as well), and will post a link here.

Sam, I have looked through that iGate thread before, and it looks pretty straight-forward. Will have to get my arms around how to make it truly mobile, so we can send it to each race venue. Best thing would be a plug and play unit and antenna that a race coordinator can attach to a computer in the host airport's FBO (or wherever a BB internet connection might be available). If the software needs to be resident on the host computer, we might have to to make it a a laptop that goes from place to place with the needed hardware and antenna along for the ride. The antenna seems the most problematic, though we probably don't need one sized for NASA mission control...like yours! kiddin'...its actually pretty cool...how'd ya talk your bride into letting you throw that up!?!?

Thanks again, and keep your fingers crossed for a little multi-plane APRS viewing this weekend!

Cheers,
Bob

Oh, by the way, as I build my XMAS list ...last time I talked to Allen, and since I plan to do the Pete Howell in-wingtip/nav light powered install, the recommended set up was an MT-8000FA, a GPS-2 GPS antenna, and a Howell Enterprises J-pole transmit antenna (which I have already procured from Pete and his son). Does that still sound like a good plan given my planned uses of general X-C, Reno Area SAR volunteering and SARL race tracking? Or has any new tech come along that I should consider?

rvmills said:

Sam, I have looked through that iGate thread before, and it looks pretty straight-forward. Will have to get my arms around how to make it truly mobile, so we can send it to each race venue. Best thing would be a plug and play unit and antenna that a race coordinator can attach to a computer in the host airport's FBO (or wherever a BB internet connection might be available). If the software needs to be resident on the host computer, we might have to to make it a a laptop that goes from place to place with the needed hardware and antenna along for the ride. The antenna seems the most problematic, though we probably don't need one sized for NASA mission control...like yours! kiddin'...its actually pretty cool...how'd ya talk your bride into letting you throw that up!?!?

Click to expand...

Bob,

I have a wonderfully patient spouse who years ago gave up trying to guess what I would drag home next.

There may be some self-contained options for an iGate (though I've never seen them) but I suspect you will need to contact an experienced ham for that info and the cost will be higher than what we are spending on our iGates and simple aviation trackers.

A dedicated laptop would be a good way to go. The only hassle you might face is the audio interface between the receiver and the iGate software. Some audio cards don't play nice with the iGate software and fiddlin' is required. But once the iGate is sorted out it would be a simple process to connect the laptop to a broadband connection and portable antenna. Here is one compact option:

http://www.gigaparts.com/store.php?action=profile&sku=ZMF-1740

Oh, by the way, as I build my XMAS list ...last time I talked to Allen, and since I plan to do the Pete Howell in-wingtip/nav light powered install, the recommended set up was an MT-8000FA, a GPS-2 GPS antenna, and a Howell Enterprises J-pole transmit antenna (which I have already procured from Pete and his son). Does that still sound like a good plan given my planned uses of general X-C, Reno Area SAR volunteering and SARL race tracking? Or has any new tech come along that I should consider?

Click to expand...

That is a proven combination which should work great.

Thanks Sam! Will keep that link and see what I can come up with this winter, and hopefully APRS Race Tracking will be a hit!

To bring this full circle to Vlad , hopefully this discussion might also help your friends in their experiment. Do Muscovite APRS trackers use the same freqs (I'm assuming it'd be in the same 2 meter band), and do you think they would have the connectivity available to make a portable or base station iGate?

It'll be interesting to hear how they skin the cat on this!

Cheers,
Bob

Bob, another idea for the iGate antenna is to get another one of P&R Enterprises' j-poles. Just put the antenna in a piece of PVC pipe and raise it as high as possible AGL. Keep the antenna oriented vertically--the j-pole is designed to work without a ground plane.

rvmills said:

....


Do Muscovite APRS trackers use the same freqs (I'm assuming it'd be in the same 2 meter band), and do you think they would have the connectivity available to make a portable or base station iGate?

It'll be interesting to hear how they skin the cat on this!

...

Click to expand...

Bob, Sam I will post the results of the experiment if any.