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APRS coverage

Leland

Leland

Well Known Member
There has been some discussion of APRS coverage in this Thread. On flying to Oshkosh from Northern California last week, at 13.5 K, I found coverage gaps in eastern Utah, Wyoming and western Nebraska. Even flying below low-lying cloud cover east of Yankton South Dakota, coverage was reasonable. Not surprisingly, areas of the country with no population seem to have poorer coverage. My Byonics Micro-Trak antenna and GPS are located on the rail behind the seats of my RV9A slider. Perhaps this is not an ideal location but it works well in populated areas like Wisconsin.
Leland



http://aprs.fi/?call=KI6RGH&dt=1216771200&mt=m&z=11&timerange=3600
http://aprs.fi/?call=KI6RGH&dt=1216857600&mt=m&z=11&timerange=3600
http://aprs.fi/?call=KI6RGH&dt=1216944000&mt=m&z=11&timerange=3600
 
Leland said:
There has been some discussion of APRS coverage in this Thread. On flying to Oshkosh from Northern California last week, at 13.5 K, I found coverage gaps in eastern Utah, Wyoming and western Nebraska. Even flying below low-lying cloud cover east of Yankton South Dakota, coverage was reasonable. Not surprisingly, areas of the country with no population seem to have poorer coverage. My Byonics Micro-Trak antenna and GPS are located on the rail behind the seats of my RV9A slider. Perhaps this is not an ideal location but it works well in populated areas like Wisconsin.
Leland



http://aprs.fi/?call=KI6RGH&dt=1216771200&mt=m&z=11&timerange=3600
http://aprs.fi/?call=KI6RGH&dt=1216857600&mt=m&z=11&timerange=3600
http://aprs.fi/?call=KI6RGH&dt=1216944000&mt=m&z=11&timerange=3600
Click to expand...

Great trip, Leland, and hope you are having a great OSH!

Perhaps for the first time, we have an opportunity to make a more or less head-to-head comparison of different APRS tracker installations. Some assumptions have been made over the past few months concerning how installation variables effect tracker performance, but maybe now we have some semi-hard data to examine.

Leland didn't specify which tracker he is using but I'm going to assume it is the 300mw version of the Micro-Trak due to the track he put down and the fact the antenna is mounted right behind his head :eek: :) . Here is a screen shot of his track nearing the Ripon approach into OSH:

RGH.jpg


Assuming Leland didn't turn off his tracker at Ripon, it appears tracking was lost as he descended to the Ripon approach altitude and no Smartbeaconing showing the turn. The bubble covers some of the beacons but some beacons were missing in the track. This is not particularly surprising since the antenna is located in the cabin (and if a 300mw transmitter is installed).

Here is a screen shot from my flying buddy Billy Baggett as he flew the Ripon approach with his 300mw Micro-Trak and a belly-mounted external whip antenna:

3AB.jpg


Notice how this tracker laid down a great series of beacons all the way to the turn to final on 36L (even the loop around Ripon....was there a crowd at Ripon?? :)).

Here is the tracker from another TVRVBG'er, Kevin Belue, who has the 8-watt MT-8000 pushing a belly-mounted external whip antenna:

7KB.jpg


Kevin sent home beacons as he was taxiing off 36L onto the grass (his last beacons didn't make it to the map for some reason). It also seems his tracker is kicking into SmartBeaconing when large speed changes occur--gotta take a look at the config of his tracker and see how he set it up.

There is no doubt an external antenna is worth the effort if maximum performance of a tracker is desired. If an internal antenna of some sort is used, and flights through very sparsely populated areas is planned, the 8-watt tracker is the way to go.

There has been discussion about the wisdom of using the MT-8000 family of trackers at full power. I certainly appreciate the concern about being a good citizen of the APRS community even though I doubt consensus on this question will ever be reached. But I have not heard any reports of problems created by the "big" trackers and it seems we can have great performance from the MT-8000's without causing any headaches to the APRS network. The above examples are interesting as we consider the impact of higher power and efficient antennae.

Happy tracking! :)
 
Last edited:
Sam,

I agree that the antenna is critical. But I see something else in your data.

The difference between 300mW and 8W was dropping 10% of the points vs. dropping 5% of the points. This is based on a small sampling, and assumes equal APRS traffic at both sampling periods. Based on the locations and the fact that they are single point losses these dropouts were likely due to ground stations transmitting at the same time as the aircraft. Apparently some ground stations were able to overpower the 8W aircraft.

Is the extra power worth it for another 5% of your tracks making it through?

As a sidebar, I wonder how much power you would have to run to get all of them through? I wonder how many would make it through with 30mW? Is it better to transmit less often with more power, or more often with less power?

As far as using 8W on an internal antenna, I have a feeling that 8W in the cabin could cause some interference issues with most intercoms, some Van?s manifold pressure gages, and maybe even your panel dimmer.:)

I know 300mW doesn't seem like much, but I think we've all seen the crazy reports of reception 200+ miles away. When I was in college, we regularly tracked weather balloons with 30mW beacons out to 150 miles (using omni antennas).

Paige
 
Sam Buchanan said:
Leland didn't specify which tracker he is using but I'm going to assume it is the 300mw version of the Micro-Trak due to the track he put down and the fact the antenna is mounted right behind his head :eek: :) . Here is a screen shot of his track nearing the Ripon approach into OSH:

Here is a screen shot from my flying buddy Billy Baggett as he flew the Ripon approach with his 300mw Micro-Trak and a belly-mounted external whip antenna:
Click to expand...

Sam, your assumption is correct, my tracker is the 300 mw version. The antenna is the $19 "manufactured" model from Byonics. It would be neat if somebody published comparable results using a wing-tip mounted antenna.

Coming home from OSH, I lost panel power and had to use a hand-held ICOM radio connected to the ELT antenna that is mounted inside the cabin. My reception was quite good but Flight Following said my transmissions were almost too garbled to read.

Question: where can I buy an adaptor to convert from the small connector on the tracker to a regular BNC cable and connector?
Leland
 
The small connector is a SMA connector. Here are some sources:

FRY's electronics

Jameco

If you have a local Ham radio store, they probably carry them also.

One thing to be careful of... A reverse polarity SMA (RPSMA) also exists for use in wireless networks, make sure the one you get has a center pin.

Paige
 
Bob,

The APRS track for N97KB is my plane. The transmitter is at the power level set at the manufacturer - I haven't changed it. I haven't checked it to see if it is 8W either. It works great, whatever the power is. Also, you'll notice on the track in to OSH that it transmits a lot in certain places. I have the Smartbeacon set to transmit more often when I slow down below about 90mph or I'm in a turn.

Kevin
RV-6A
RV-10
 
PaigeHoffart said:
Sam,

I agree that the antenna is critical. But I see something else in your data.

The difference between 300mW and 8W was dropping 10% of the points vs. dropping 5% of the points. This is based on a small sampling, and assumes equal APRS traffic at both sampling periods. Based on the locations and the fact that they are single point losses these dropouts were likely due to ground stations transmitting at the same time as the aircraft. Apparently some ground stations were able to overpower the 8W aircraft.

Is the extra power worth it for another 5% of your tracks making it through?

As a sidebar, I wonder how much power you would have to run to get all of them through? I wonder how many would make it through with 30mW? Is it better to transmit less often with more power, or more often with less power?

As far as using 8W on an internal antenna, I have a feeling that 8W in the cabin could cause some interference issues with most intercoms, some Van’s manifold pressure gages, and maybe even your panel dimmer.:)

I know 300mW doesn't seem like much, but I think we've all seen the crazy reports of reception 200+ miles away. When I was in college, we regularly tracked weather balloons with 30mW beacons out to 150 miles (using omni antennas).

Paige
Click to expand...

As I stated in my original post, I doubt we are going to reach consensus on how much power is "correct". :)

My main point was how eight watts will be advantageous when flying in areas of sparse population. The examples I cited certainly aren't a scientific sample but are the first time I've seen three different tracker configurations in the same area in a short period of time. Just thought it was interesting to compare the performance of trackers where we knew the particular setups.

Bob Brown said:
Sam-Do we know that Kevin had the 8w tracker turned all the way up?
Click to expand...

Bob, I am almost certain Kevin is running the MT-8000 as it came out of the box--full power.
 
Leland said:
Sam, your assumption is correct, my tracker is the 300 mw version. The antenna is the $19 "manufactured" model from Byonics. It would be neat if somebody published comparable results using a wing-tip mounted antenna.
Click to expand...

Leland, there are numerous 300mw trackers running Pete Howell's wingtip antenna. Check out the "Airplane Tracker" sticky at the top of this forum to see how Pete's original setup performed. This has proved to be a good combination and I think you will see a much improved track if you decide to use Pete's antenna. If you go with the wingtip antenna you might as well put the tracker and GPS out there as well. See Pete's installation for more detail.

Looks like you made it safely back to the Left Coast! :)
 
Sam,

It would be interesting to see just how much an 8W transmitter would extend your range in a sparsely populated area. VHF is primarily limited to line of sight; you can go beyond line of sight through diffraction but I'd be surprised if you got more than an additional 10% out of it.

Line of sight at 10,000' is about 140 miles; a 300 mw transmitter with isotropic (spherical radiation pattern) antennas at both ends will put a 2.6uV signal into the receiver, 8W will put a 13.7uV signal into the receiver (a cheap mobile ham transceiver has a sensitivity of 0.2uV). The theoretical range I came up with for 300mW is 147 miles. For 8W, I come up with 157 miles.

This is all based on flat terrain and average soil. If you're flying over mountainous terrain, you'll probably see a greater improvement due to knife edge diffraction.

I'm doubtful that the extra 10 miles is going to do much to close coverage gaps. Unless you have some serious antenna issues (like 15dB loss) I think an 8W transmitter would be much more useful in a ground based transmitter, since path losses can be much higher there due to obstructions.

Anyone have any empirical data?
Anyone want to check my math?

Paige

BTW, I'm not trying to tell anyone what the "correct" power is; I'm just showing why I don't see the utility.
 
PaigeHoffart said:
Sam,

It would be interesting to see just how much an 8W transmitter would extend your range in a sparsely populated area. VHF is primarily limited to line of sight; you can go beyond line of sight through diffraction but I'd be surprised if you got more than an additional 10% out of it.

Line of sight at 10,000' is about 140 miles; a 300 mw transmitter with isotropic (spherical radiation pattern) antennas at both ends will put a 2.6uV signal into the receiver, 8W will put a 13.7uV signal into the receiver (a cheap mobile ham transceiver has a sensitivity of 0.2uV). The theoretical range I came up with for 300mW is 147 miles. For 8W, I come up with 157 miles.

This is all based on flat terrain and average soil. If you're flying over mountainous terrain, you'll probably see a greater improvement due to knife edge diffraction.

I'm doubtful that the extra 10 miles is going to do much to close coverage gaps. Unless you have some serious antenna issues (like 15dB loss) I think an 8W transmitter would be much more useful in a ground based transmitter, since path losses can be much higher there due to obstructions.

Anyone have any empirical data?
Anyone want to check my math?

Paige

BTW, I'm not trying to tell anyone what the "correct" power is; I'm just showing why I don't see the utility.
Click to expand...

I have flown both the 300mw and 8-watt versions of the Micro-Trak, both with the same external whip antenna. I don't have a clue as to the "theoretical" range of the two trackers, but the higher-powered rig definitely lays down a more consistent track than the low-power tracker, especially at low altitudes. The performance of the MT-300 is good at low altitude, but the performance of the MT-8000 is superb.

I like superb. :)

Nearly all my flying is less than 5000' AGL and in hilly terrain so I'm not sure how relevant the above calculations are to my flights.

But....I don't want this matter of "range" to progress into an endless discussion about aspects of APRS that are almost impossible to verify. What we can all agree on is the wonderful addition to our aircraft that APRS represents, and the enjoyment many of us receive from this aspect of amateur radio.
 
Last edited:
Sam,

I'm sure 8W works better for your mission. Maybe I should have said low altitude environment instead of "ground based transmitter".

I ran the numbers at 10,000' AGL because the original poster said he was at 13,500 when he experienced the coverage gaps.

My feeling is that the gaps he experienced were due to lack of ground stations, or poor antenna performance, but not lack of power.

Paige
 
Will the Micro-Trak unit also act as a digipeater? Even at 5000 feet what a way to extend the range of the APRS network... :)

I pulled my old Kantronics KPC-9612 TNCs out of the box and wired one up to a ham handheld at 144.39. Listening on 144.39 without the TNC hooked up, I could hear packets being received from other stations, but as soon as I turned on the TNC I'd get nothing. I was monitoring from a second radio to verify, but sure enough, my TNCs (both of them) are causing interference on 144.39 when they are powered on. What a PITA. *sigh* Unfortunately I don't have any other radios that I can put on that freq. When I had them setup previously, I was playing with 9600 baud on the 440Mhz band, and had never tried on 2m before.

-Dj
N1JOV
 
deej said:
Will the Micro-Trak unit also act as a digipeater? Even at 5000 feet what a way to extend the range of the APRS network... :)

I pulled my old Kantronics KPC-9612 TNCs out of the box and wired one up to a ham handheld at 144.39. Listening on 144.39 without the TNC hooked up, I could hear packets being received from other stations, but as soon as I turned on the TNC I'd get nothing. I was monitoring from a second radio to verify, but sure enough, my TNCs (both of them) are causing interference on 144.39 when they are powered on. What a PITA. *sigh* Unfortunately I don't have any other radios that I can put on that freq. When I had them setup previously, I was playing with 9600 baud on the 440Mhz band, and had never tried on 2m before.

-Dj
N1JOV
Click to expand...

Here is a quote from the Micro-Trak Yahoo group by Allen Lord, designer of the Micro-Traks about an upcoming product:

"The second product we showed was a Micro-Trak based on the TinyTrak 4
controller. This device will allow you to send and receive tracking
information, and display it on your PC, our compatible GPS display
receiver. Byon is also working hard right now on developing
digipeater firmware for this unit."

Looks like that will be your airborne digi. :)
 
Sam Buchanan said:
Here is a quote from the Micro-Trak Yahoo group by Allen Lord, designer of the Micro-Traks about an upcoming product:

"The second product we showed was a Micro-Trak based on the TinyTrak 4
controller. This device will allow you to send and receive tracking
information, and display it on your PC, our compatible GPS display
receiver. Byon is also working hard right now on developing
digipeater firmware for this unit."

Looks like that will be your airborne digi. :)
Click to expand...


Could this be the path to our own airline like ACARS system?
 
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