Cheap and Simple Backpackable APRS

Disclaimer: The information on this website is pretty old. I haven't updated it in years, and I no longer use the FD-160. By the time you read this, APRS probably uses touch-tones over mental telepathy or something else. You are welcome to look around, but don't take this as anything close to representing the state of the art of APRS.

Martin, KI6WJP 8/6/2020

Making a cheap, backpack portable APRS tracker

If you got here by following a link in my APRS status, you already know, but if you got here some other way, you may want to read about APRS here.

My Tracker has 3 main components:

1. handheld transceiver
2. gps receiver
3. APRS tracker cpu

My transceiver is an FD-160A purchased from a seller in Hong Kong on e-bay. Total cost including shipping was less than $60. This is a 2 Meter radio manufactured in China by Quanzhou Feidaxin Electronics. The manufacturer says the radio is capable of transmitting at 5 watts. My service monitor says that high power is 3 watts. Low power is 2 watts. Other than somewhat lower power than spec, the radio meets the specifications. The English version of the manual is nearly incomprehensible, but I managed to figure it out. In general, this is a good starter handheld transmitter. Probably the biggest failing is the lack of DTMF. Since I am using it for APRS, this is not a problem.

My gps receiver is a 'GPS3" was purchased from byonics. for $64. This is a totally bare bones receiver without any sort of case. This uses the SiRF Star 3 chipset and draws about 65ma.

There are several choices for the CPU for the tracker. One option was to roll my own using source and schematics from around the internet. I may end up doing that, but I was impatient to get something working, so I narrowed the choice down to the byonics tinytrack3 ($33 kit) and the Argent Data Open Tracker 1+ ($32 kit). I decided on the Open Tracker because the source code is available. I'm not a real fan of the freescale processor used in the OT1+, but any source for a less than desirable CPU is better than nothing for a great one.

After soldering the kit together and building some connecting cables, I had a complete APRS tracker for about $160. The whole package is kept in a small tupperware type container.

For use in the car, the tracker is powered with a 12 volt converter from the car battery and a mag-mount quarter wave whip antenna.

For backpacking, the unit is powered from the radio battery using the stock radio antenna. With the radio powering the tracker and GPS, the battery lasts about 9 to 10 hours. I need to see how long it lasts when on low power (2 watts).

Trips with the Tracker

Coast Starlight

One of the first big trips after getting the tracker working was a ride on the Amtrak Coast Starlight from Dunsmuir to Santa Barbara. I sat the tracker on the window sill in our "room". Given that an amtrak train is a big metal box, and I was using a lousy antenna at 3 watts, I was surprised that any packets made it out. The battery ran dead somewhere around San Luis Obispo.

Mount Shasta Climb

In June of 2009, boy scout troop 97 began a series of practice climbs on Mount Shasta in preparation for a summit attempt some time in July. Here is what the track looked like to Helen Lake at 10000 feet elevation.

The tracker was configured to transmit once every 5 minutes. All of the packets below 7600 feet in elevation did not get picked up by any digipeaters. Once we got above 8000 feet, then most of my packets were picked up by my igate at my house 8 miles away. On the way up to Helen Lake, most of the packets made it to the internet, but on the way down, most of them were lost because the tracker is in the outside pocket of my backpack and was facing away from the igate/digipeaters.

Later, for conditioning purposes, we climbed Mt. Lassen. Here is the track from the Mount Lassen Climb.

In this case, the closest digipeater was about 40 miles away. At the trailhead, none of the packets got out, but once we got to the main ridge we had pretty good success in getting out.

So far, the longest that my tracker has been heard is 186 miles. Not bad for a handheld radio with a lousy "rubber duck" antenna. This was while climbing Mt. Lassen at 9000 feet elevation. Most of my packets were picked up by digipeaters about 40 miles away, but one got caught by W6CX-3 in the hills above Oakland.

On July 20, 2009, after two months of conditioning hikes, the scout troop made the big push to climb Mt. Shasta. I ended up getting sick, and stopping at the base of misery hill. The rest of the climbing party made it to the top.

I was a bit surprised that I did not get better coverage from the APRS system. All of the packets were received by my home IGATE. There are gaps where my home was behind a ridge. I would expect that at least the Redding digipeater would have picked up in those areas that are not covered by my home IGATE.

APRS on the Pacific Crest Trail. Sept 6, 2010

Over Labor Day weekend, my family hiked 5 miles along the pacific crest trail to Porcupine Lake. On the way in, I carried my tracker with a modified rubber duckie antenna. Here is resulting track.

The tracker was configured to transmit every 5 mintues. Only 3 packets were picked up until we crossed around the shoulder of porcupine peak where we were line of sight to the Mount Shasta Igate. In spite of 3 watts and the poor antenna, several of the packets where picked up by a digipeater 107 miles to the east.

In preparation for the PCT Golden Packet Event, I built my own Arrow J-Pole which breaks down to a bundle about 20 inches long. I carried it in to see how well it worked with my handheld once we reached camp. The results were great. The next day, on the way out, I decided try the Arrow J-Pole with my tracker. I tied my Arrow J-Pole antenna to my backpack and hooked it to the tracker. Here is the resulting track:

This track is much better. Every packet got out to the internet except for three packets. There are no digipeaters to the west, so coverage is poor when on the west side of the ridge. The Arrow J-pole is a wonderful antenna; However, it is nearly 6 feet long and sticks up about 3 feet above the top of my backpack. When I left the trail briefly for a break, I got hung up in branches. Fortunately, the Arrow is pretty sturdy, so nothing got bent. Here is the arrow website. I recommend their antenna without reservation. http://www.arrowantennas.com/

Troop 97 hiking in Castle Crags State Park

On Sept 18, 2010, Troop 97 hiked to the base of the "dome" in castle crags state park. Here is the track.

I didn't get the best coverage (I didn't carry the big arrow j-pole). Less than half the packets got to the Internet. The weather was forecast to be heavy rain. Fortunately, it held off until after we got back to camp.

APRS Coverage along Interstate 5 in California

This image shows the typical coverage I get on Interstate 5 using a 1/4 wave mag mount whip antenna.

Generally, Interstate 5 has good coverage with a minor gap between Orland and Willows. However, north of Redding, as you get into the hills around Shasta Lake, the coverage gets really spotty. For the most part this is understandable, but the SHASTA digipeater should do a better job once you reach Castella. My home APRS system hears cars driving by on I5 that never get digipeated by the SHASTA digipeater. The Shasta digipeater is on Soda Ridge above Dunsmuir. It has good visibility of I5 for at least 20 miles, but very few packets get picked up.

There is a big hole in coverage north of Black Butte to the Siskiyou Summit. We really need a digipeater that covers the Shasta Valley.

Smart Beacon Rates

The APRS forum at Vansairforce.net was the thing that got me interested in APRS and re-sparked my interest in ham radio. The quick start guide there in my opinion is offering some poor advice on configuring smart beaconing.

This shows an aircraft making a complete circle in 40 seconds at 1900 feet altitude. The tracker was configured with a wide2-1 path. All 10 packets were received directly by igates. Packets were being transmitted at a rate of 1 every 4 seconds. There are at least 5 digipeaters within 30 miles of this location. It is likely that all 5 digipeaters heard the packet, and unless it was corrupted, the packet was re-transmitted. That means that this single circle generated a flood of 50 packets over a 40 second period.

This is NOT what APRS was designed to do. If you want to draw pretty pictures in the sky, please be careful that you are not saturating our precious shared frequency. At most, your UI Path should be WIDE2-1. If you are in an area with good coverage by igates, consider no path at all. If 80 percent of your packets are getting through, then APRS is working as designed.

Here is the configuration as suggested on vansairforce

The "Min Turn Time" is the number of seconds that must pass before retransmitting while turning. In my opinion, this should never be shorter than every 30 seconds.

Airplane APRS users need to be very careful how their trackers are configured. At high altitude, a low powered tracker will transmit more than a hundred miles. If you send a packet every 5 seconds, you will be tying up a very limited resource for hundreds of miles around you.

My next point, is that beaconing every 60 seconds is approaching the limit of what is considerate. Yes, I know that you are moving at 3 miles per minute, but when you are moving in a straight line, I can extrapolate your position quite closely based upon your speed and direction at the time you last transmitted. If you turn, then the smart beaconing kicks in and sends out a packet to show that you turned the corner.

In my car, I have the smart beacon set to transmit no more frequently than 30 seconds. My beacon rate is 180 seconds. These settings conform to the suggested values at http://info.aprs.net/index.php/NorCal_APRS_Regional_Info

Paths for mobile use in California

WIDE1-1 works nearly everywhere in California. Use WIDE1-1,WIDE1-2 only if needed.

Let's look at this objectively. The world doesn't care about your perfect trail of packets. A Missing packet here or there isn't cause for alarm. If 80 percent of your packets are making it to the Internet, then APRS is working as designed. Nearly every digipeater in California has at least 1 igate in its coverage area. More than 1 hop is just adding to congestion on the channel without significantly increasing the number of packets that get to the Internet.

Consider this trip between LA and Stockton with a two hop WIDE1-1,WIDE2-1 path. Over the entire trip between LA and Stockton, all packets except 12 made it in a single hop. Other than the 80 miles between Kettleman City and Firebaugh, a WIDE1-1 path would have been perfectly adequate. If you live in that area, an Igate would be a good addition.

There are a few places in the canyons or mountains where there is no coverage at all. Adding another hop to your path won't help get your packet to the Internet. If you routinely travel in an area without coverage, consider adding a fill-in digipeater. Don't add to your path in the vain hope that somebody will hear you.

The above is written for the APRS user who has only viewed APRS on the Internet. If you follow APRS over the air, then you probably already know all this.

Self Contained Battery Life

One of the most useful configurations of my tracker is the self contained "backpack mobile" mode. In this configuration, the tracker and GPS receive power from the radio battery. Usually, I have the tracker programmed to transmit every 5 minutes rather than use smart beaconing. On the Mount Shasta climb, the radio was set to "high" power (3 watts). The battery lasted until 10:00am. I think I turned on the tracker around 1:30am, so that means I got 9.5 hours of use from the battery.

I have since done some testing and have found that I can get 11.5 hours of use from the radio battery if I use "low" (2.5 watts) power. The interesting thing is that the OpenTracker reports that the voltage drops from 7.4 volts to 6.5 volts in 2 hours, then stayed there until the radio stopped transmitting 8 hours later. It might be that the below 6.5 volts, the 7805 regulator is allowing the 5 volts to drop, so the A/D reference voltage is sagging along with the battery. A low dropout regulator instead of the 7805 may help with this.

I think that the GPS is probably drawing more power than necessary. It has a LED on all the time it has a satellite lock. If I get really ambitious, I'll dig into the source code and try to figure out how to put the GPS into low power mode in between transmissions. I also assume there may be a way to put the tracker CPU itself into low power "sleep". I should be able to keep the realtime clock running so it can wake itself up. If I do this, then the smart beaconing won't work, but I'm hoping I can get enough battery to last an entire day. With the radio alone, the battery lasts nearly 3 days.

On the coast starlight trip, the battery lasted about 15 hours. The battery was brand new and I was using smart beaconing. Smart becaconing may be the way to go. For backpacking, I find that the trails are seldom straight, so I decided that smart beaconing would be transmitting every time the trail made a jog to get past a tree or boulder. However, I'll need to try it out on a real hike to see how well the smart beacon code works when you are on a winding path. I guess I could set the min transmit time to 5 minutes. I may give it a try sometime.

Pacific Crest Trail Golden Packet Event. July 24, 2011

On July 24, 2011, hams are hoping to send an APRS packet from Mexico to Canada roughly following the route of the Pacific Crest Trail. I have volunteered to place a digipeater on Mt. Eddy in Northern California as part of this event.

Here are some google earth screen shots showing two possible paths from Mt. Eddy. This shows the path to the north. In the distance is "The Watchman" on the northwest rim of Crater Lake 113 miles to the north.

130 Miles to the south, Saint John Mountain has an easy line of sight path. 121db of free space loss. We should be able to talk from peak to peak with a 5 watt handheld radio.

I will be using my GE MVS radio (heavy, but built like a tank) with a Kantronics KPC3+ TNC as a digipeater. I know that Bob doesn't like the KPC3+, but I'm confident that I can properly adjust the deviation and levels. I will be using an open stub J-Pole which has good gain.

I'll hike in to upper deadfall lake the day before the event. This is about 3.5 miles most of which is along a dead level stretch of the PCT. The last half mile is a pretty good uphill climb to the lake. I'll spend the night on the meadow at upper deadfall lake. Sunday morning, I'll make the 1.5 miles to the summit. After the last packet on Sunday, We'll break everything down and hike out 5 miles. Alternatively, I can come in from the east via the Sisson Calahan trail. This is a somewhat shorter route, but involves more elevation gain. I'm hoping to have at least 1 or 2 other people along to help carry gear. (12VA gel cell batteries aren't light.). If you are interested, give me a shout.

If you want more information about the PCT Golden Packet Event, read about it at http://aprs.org/pct-golden-packet.html

As of June 3, 2011, only 2 sites have committed to be activated. Mt. Eddy and Arnold,CA. Bob B suggested St. John Mountain west of Willows. This has a clear shot to Mt. Eddy, and a somewhat obstructed 150 Mile path to Arnold. In both cases, the path loss is around 122dB so APRS should work just fine.

Here is my map of the PCT Golden Packet sites as of 7/16/2011

APRS via the International Space Station

Many hams have a goal of making contact via satellite. The easiest way of doing this is to use APRS via the ISS. Here are the things that I used to make contact via the ISS:

Windows 2000 PC with serial port.

UISS http://users.belgacom.net/hamradio/uiss.htm An easy to use AX25 UI program optimized for satellite usage

Orbitron http://www.stoff.pl A free satellite orbit tracking tool

AGWPE http://www.sv2agw.com/downloads/default.htm AGW Packet Engine to connect to TNC

Opentracker KISS TNC

Transmitter on 145.825mhz

I have heard of people using a 5 watt handheld with a directional antenna. I tried my 3 watt handheld, but never got digipeated. To make contact, I used a 40 watt GE MVS commercial radio reporgrammed to the 2 meter ham band.

I watched the orbitron screen as the ISS came up over the horizon to the northwest. I began to hear noisy packets as it rose above 10 degrees. Every minute or so, I transmitted my location. Once it was about 15 degrees above the horizon, I heard my beacon digipeated. On this particular pass, the ISS only reached 17 degrees above the horizon, so I only got one packet digipeated. A ham in canada replied to me, but my response never got digipeated.

http://ariss.net/ is a website that tracks APRS stations which have been digipeated by the ISS. Here is a snapshot of the screen after I got digipeated:

here is the raw traffic from the ISS around the time when I got digipeated:

00:00:00:56 : VE6EGN]CQ,RS0ISS-4*,qAR,WA6LIE-4:hi to ki6wjp<br> 00:00:01:33 : AI7W-1]CQ,RS0ISS-4*,qAR,N6VUD-2:=4403.59N/12303.44W-Steve Eugene, Oregon [CN84lb] {UISS40}<br> 00:00:01:48 : W6XLR]APU25N,RS0ISS-4*,qAR,WA6LIE-3:=3737.28N/12205.12W-Rich, CM87<br> 00:00:02:30 : RS0ISS-4]CQ,SGATE,qAR,WA6LIE-3:]ARISS - International Space Station (BBS/APRS on)<br> 00:00:02:45 : AI7W-1]CQ,RS0ISS-4*,qAR,WA6LIE-4:=4403.59N/12303.44W-Steve Eugene, Oregon [CN84lb] {UISS40}<br> 00:00:03:35 : AI7W-1]VE6EGN,RS0ISS-4*,qAR,WA6LIE-3:It's been a while.<br> 00:00:03:42 : KI6WJP]APRS,RS0ISS-4*,qAR,N6VUD-2:=4117.56N/12219.12W-Hi from Mt Shasta, CA (CN81) {UISS52}<br>

This reads from the bottom up. (The time stamp is how recent the packet is.) You can see that VE6EGN said hi to me, but I never saw his packet over the air.

Contacting Me

If you want to send me an email, try firstname.lastname@gmail.com.