# Homebrew GPS Tracker

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#### ksaves2

Wowsers. That took longer to find than I'd anticipated..... https://www.gnss.store/gnss-gps-mod...s-receiver-board-with-sma-for-uav-robots.html Still available but slightly different and certainly more expensive.... I seem to remember that after the Ublox5 was released, although the chipsets became more sensitive and you could pick up GNSS satelites that the dynamic performance became legally reduced to prevent use in guided things that hurt people.
Wow Norman, That form factor would be easier to mount in a rocket. Nonetheless, The GPS trackers out there are sufficient to effect a recovery. One tip I like to give is blow the main at as high an altitude that one's launch venue would be practical with. Under a good main, the positions are more likely to stream in and give a drift pattern. In a large enough field I'll blow the main at 1000'. Altitude is good for radio propagation.
Just out of curiosity, I went downstairs and found out I saved the dead ublox 5 GPS module with the amplified helical antenna. I also found my prototype EggFinder I hacked with a GPS chipset I think I bought from an English concern. I don't remember the designation offhand. I originally dropped the EggFinder and the patch antenna broke off the base. It ended up in my junk drawer until I decided to desolder the base and added this GPS (from England) with a helical receiver antenna with two wires. This GPS chipset isn't amplified but gave really good performance using GPS and the Glonass constellations. I notice the helical antenna is a little shorter than the Ublox 5 unit. Dang! I wished I would have spent the $400.00 or so to get some backup Ublox units when they were available. I recall it gave excellent performance even from my basement. I presume the receiver amplifier was the key there. Once my son is done using the computer to watch videos, I'll stick the units on the scanner and post them. Kurt #### jqavins ##### Helpful Smartass TRF Supporter Easy, you are trading your time to save money, simple as that. You can spend 5 minutes ordering a tracking system that is complete and ready to go for about$400, or one that requires an hour or three of your time for about $200, or you can try and build one yourself for even less money but potentially far more time. There is a direct correlation between how much money you spend vs. how much time you spend. So you are chasing money - you said you were a cheapskate and a goal of DIY was to save money. You can only save your money by spending your time on coming up with a DIY tracker, and you said only if it saved you a minimum threshold. It seems to me you have set a specific value on what your time is worth, so Time = Money. I have a nebulous value on the time and trouble I'd spend to save money. But the meaning of the phrase is that spending time costs money. Several people have suggested that the cost of making one's own is the price of parts and the price of time used. Giving up time is costly. Time = Money. Whereas in what I'm proposing, giving up one is saving the other. Give up time and exert effort to save money (homebrew) or give up money to save time trouble (purchase). The effort involved is more of the potential reason to purchase; it's cheapskate vs. lazy. Last edited: #### manixFan ##### Not a rocket scientist I have a nebulous value on the time and trouble I'd spend to save money. But the meaning of the phrase is that spending time costs money. Several people have suggested that the cost of making one's own is the price of parts and the price of time used. Giving up time is costly. Time = Money. Whereas in what I'm proposing, giving up one is saving the other. Give up time and exert effort to save money (homebrew) or give up money to save time trouble (purchase). The effort involved is more of the potential reason to purchase; it's cheapskate vs. lazy. I think most people understand that if 'spending time costs money' then if follows that 'saving money costs time'. But it all depends on perspective of course. You're doing the latter instead of the former, but the net result is the same, Time = Money. Not trying to beat a dead horse, just an interesting exercise in semantics and verbal math. Tony #### boatgeek ##### Well-Known Member I think most people understand that if 'spending time costs money' then if follows that 'saving money costs time'. But it all depends on perspective of course. You're doing the latter instead of the former, but the net result is the same, Time = Money. Not trying to beat a dead horse, just an interesting exercise in semantics and verbal math. Tony With many of my projects, it turns out that saving money costs time and a lot more money. I may be doing it wrong. #### jderimig ##### Sponsor TRF Sponsor Productive time = value = money. While you are making your own tracker you instead could use that time to trim your neighbor's bushes for enough compensation to buy a fully sorted tracker. #### tsmith1315 ##### Well-Known Member Easy, you are trading your time to save money, simple as that. I gotta agree with Joe. If the time you are trading has monetary value. That's only the case when you are using time that would have been used to generate income. If there's a zero chance that portion of time would have been used to generate income, that is literally free time. However, it can still be precious. #### gtg738w ##### FlightSketch - flightsketch.com The issue I perceive with the patch chip antenna on a flat board mounted vertically is that rockets spin, generally. Usually to help keep them straight in flight. So if you stand and hold your arms out you get the reception pattern of a chip antenna. That is everything in front of you and most of the front sides. Half of the sky....... Now if you start spinning all those satellites are going to go hello/ goodby depending on your rate of spin. A ceramic patch uses the ground plane as part of the antenna structure. Most will have an almost equal peak on the back side so there is no "dead zone". Mounted vertically on the pad or in flight you still have very useable gain over the entire sky. I recall it gave excellent performance even from my basement. I presume the receiver amplifier was the key there. GPS signals are already weak enough to be limited by noise. Adding an amplifier will actually degrade the signal to noise ratio at that stage. You can't just boost signal strength for free, the antenna still has to do its job. Low noise amplifiers are used to minimize the noise impacts from downstream components in the chain - cables or filters/amps in the front end. You'll see active antennas listed as +20dB but it could be a -5dB antenna gain with 25dB of amplifier gain. The actual antenna gain is what matters most but if you also want an isotropic pattern, there is a physical limit on performance. #### Tetrahedron ##### Well-Known Member Nope. For me that's a completely irrelevant question. I have no interest in entrepreneurship; I just want a GPS tracker and I'm scared off by the prices. (I had not found the$100 Eggfinder system.) As I said above, I know I can't build a car for less than I can buy one. On the other hand, I know I can cook a damn good steak for less than I can buy it at a restaurant. I'm not trying to open a steakhouse.

is the time that I put into it ($0) plus any parts I may burn up in the process. Update: I checked out the Eggfinder system. For what I have in mind I'd have to buy the basic transmitter ($70), the LCD handheld receiver kit ($55) and LCD GPS module add-on ($40). So $165. That's not unaffordable, but I'm a cheapskate. If I can do it myself for$65 and save a hundred bucks, that's probably worth it. If I can do it myself for $140 and save twenty-five, that's not. Yes, I did it and it's about$65 in parts and it works pretty good, not perfect. It took me some time searching online and watching youtube videos.
I'm using LoRa modules at 433 Mhz (or 916Mhz for license free) and uBlox GPS (or others) and a fast processor on a development board like ARM Cortex M0+.
The code is all Arduino and I know others have done it too.

-John

#### rokit

##### Well-Known Member
I have a nebulous value on the time and trouble I'd spend to save money.
My comment was meant to try to quantify some of the positive values of spending time. Sorry if that wasn't clear. To hopefully make things more clear, I support you investing time towards this effort. I tried it myself, learned a few things, and enjoyed it more than whatever I would have done otherwise.

#### manixFan

##### Not a rocket scientist
...<snipped for brevity>...
Update: I checked out the Eggfinder system. For what I have in mind I'd have to buy the basic transmitter ($70), the LCD handheld receiver kit ($55) and LCD GPS module add-on ($40). So$165. That's not unaffordable, but I'm a cheapskate. If I can do it myself for $65 and save a hundred bucks, that's probably worth it. If I can do it myself for$140 and save twenty-five, that's not.
I have a nebulous value on the time and trouble I'd spend to save money. But the meaning of the phrase is that spending time costs money. Several people have suggested that the cost of making one's own is the price of parts and the price of time used. Giving up time is costly. Time = Money.

Whereas in what I'm proposing, giving up one is saving the other. Give up time and exert effort to save money (homebrew) or give up money to save time trouble (purchase). The effort involved is more of the potential reason to purchase; it's cheapskate vs. lazy.
Since the idea of time = money seems to have become a big part of this thread, I think it's fair to expand on it a bit more. Folks seem to be on both sides of the fence on the time = money equation, in that time only has a monetary value if you can get paid for it. I provided what I consider to be a corollary argument, that money can be used to save time, or time can be used to save money. The net result is the same, how much time you spend on a project can correlate to how much money you spend, In that case, you are basically paying someone else to save you time, which gives a value to time in terms of cost to you.

jqavins - I don't think you have a nebulous value on your time - look at the first post quoted above. If you can save $100, you'd pursue a DIY tracker. But if you can only save$25, you'd pass. So you seem to have a pretty good idea of what your time is worth, even in the absence of time = income.

I realize that many reading this will think it's a trivial argument. But I find this an interesting discussion because I have been somewhat irrational at times at the amount of time I'll spend to save a few dollars, when clearly the reward in the end was not saving money, but having learned something new or gained additional experience. That in and of itself is reward enough to do many things even though I may have been able to purchase a less expensive alternative, especially when time is factored in. I find it helpful to understand my true motivation behind a particular project in order to best try and accomplish my goals.

Tony

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#### ksaves2

A ceramic patch uses the ground plane as part of the antenna structure. Most will have an almost equal peak on the back side so there is no "dead zone". Mounted vertically on the pad or in flight you still have very useable gain over the entire sky.

GPS signals are already weak enough to be limited by noise. Adding an amplifier will actually degrade the signal to noise ratio at that stage. You can't just boost signal strength for free, the antenna still has to do its job. Low noise amplifiers are used to minimize the noise impacts from downstream components in the chain - cables or filters/amps in the front end. You'll see active antennas listed as +20dB but it could be a -5dB antenna gain with 25dB of amplifier gain. The actual antenna gain is what matters most but if you also want an isotropic pattern, there is a physical limit on performance.
Agreed Russ,
I have to say that Ublox 5 with the helical antenna was advertised as amplified so likely used a low noise amp and probably was filtered. I remember it was the
best performing chipset I saw. Another comment is to the cost debate. I messed around because I liked working and learning from the electronics. All in all I probably spent a fair amount of dollars and I looked at it totally as a learning experience. I agree, it's simpler just to buy a unit rather than prototype and build one's own. Only reason to build is because one likes to build. For that there are GPS tracker kits out there. Kurt

#### Dan Griffing

##### Well-Known Member
TRF Supporter
Why? How? I challenge anyone to provide a justification for that statement which surpasses the below.

dupe

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TRF Supporter

#### manixFan

##### Not a rocket scientist
This is getting way off topic and into classic issues about the fundamental issues of economics.
I respectfully disagree. The OP has responded multiple times with his reasoning and approach to the issue of the time = money. If the OP was ignoring it or objecting to the discussion, then I would say it is off-topic. But since the OP is actively engaged in the conversation, I don't see how it can be off-topic. Money was part of the original proposition, so it seems relevant to the discussion.

Tony

#### jqavins

TRF Supporter
"Off topic"? Well, it's gone pretty darn far off on a tangent. Just not unwelcomely so.

#### GrouchoDuke

##### Well-Known Member
Designing your own rocketry electronics is a pretty all-encompassing significant life & emotional event -- I'm pretty sure everything is on topic.

#### Dan Griffing

##### Well-Known Member
TRF Supporter
Designing your own rocketry electronics is a pretty all-encompassing significant life & emotional event -- I'm pretty sure everything is on topic.
I’m not against designing your own rocketry electronics. But I’m doing it for things that I need but can’t readily buy for less money or time.

As a retired engineer, I know what’s involved in developing a professional quality instrumentation electronics PCB and getting it right. While working I frequently decided whether it was better to build or buy. This is the same decision rocketeers make on designing and building their own rocketry electronics. Its not rocket science.

DIY doesn’t have to be for everything.

#### cerving

##### Owner, Eggtimer Rocketry
TRF Supporter
That reminds me of an old Steve Martin sketch (I couldn't find the video, unfortunately). He's talking about his neighbor the engineer, and a conversation he had with him, his neighbor says incredulously..."You bought one of those? You really bought one of those?....

You bought a refrigerator?"

#### ksaves2

Here is a scan that shows the Eggfinder with a helical antenna Uputronics GPS that is OOP. Uputronics still has some neat stuff on its site: Uputronics

The Uputronics GPS the receiver is not amplified but still with good performance. The loose GPS is the Ublox 5 that had an amplified receiver in it. The antenna has a beefier base to it. It worked very well but as I mentioned before I dropped it and broke it. I did have it plugged into that EggFinder prototype and saw excellent performance.

Once Sarantel was sold, I couldn't find anymore small amplified GPS chipsets. There is an amplified GPS receiver antenna with an SMA plug on the Uputronics site that I suppose could have the cable cut down and used in a tracker for a larger rocket. Have to provide more battery juice I expect to power the antenna, receiver and radio.

It just takes two wires to the Eggfinder and I believe the EF had a 5V out terminal and that's what I used to power the GPS. I think most GPS units now are 3 volts or lower so that has to be taken into consideration for rolling your own. My contention is roll your own only if one enjoys doing it and has the skills. I spent money learning the minimal skills and I certainly can't design a system from the PC board up. Kurt Savegnago
(Sorry the scan is sub optimal but my camera is on the fritz)

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#### OverTheTop

##### Well-Known Member
TRF Supporter
My situation is that I spend $100-200 (or maybe less) and several days to a few weeks on a mid power rocket, stick a single use G80 in it, and never see it again because it is lost in the waist-high grass where an hour of walking a search pattern turns up nothing. After this has happened over and over, I need a locator, and am willing to save$100 bucks by doing it myself, if that's feasible, which is where the whole thread started.
You are so going to love the feeling when you use your GPS tracker and walk up to the rocket the first time .

#### RocketScientistAustralia

##### Well-Known Member
All things in life are a trade off. All antennas have good points and bad points. A Yagi can have great amplification, but can be limited to a very narrow viewing field. A Quadrafilar Helical antenna has good omnidirectional reception but needs amplification. Each is a trade off. The patch antenna has a reception lobe front and back. The one at the back is 10 dB down on the front. That is 1/10th of the signal is received from the back. And 30dB down at some of the holes in the reception lobes.
Most Satellite phones, and GPS is just a satellite connection, use Quadrafilar Helical antennas.
They are certainly worthy of testing side by side with a patch antenna in a real rocket world to see which provides the best real world performance. And I'm surprised the test has not been done or offered as an option.

#### ksaves2

All things in life are a trade off. All antennas have good points and bad points. A Yagi can have great amplification, but can be limited to a very narrow viewing field. A Quadrafilar Helical antenna has good omnidirectional reception but needs amplification. Each is a trade off. The patch antenna has a reception lobe front and back. The one at the back is 10 dB down on the front. That is 1/10th of the signal is received from the back. And 30dB down at some of the holes in the reception lobes.
Most Satellite phones, and GPS is just a satellite connection, use Quadrafilar Helical antennas.
They are certainly worthy of testing side by side with a patch antenna in a real rocket world to see which provides the best real world performance. And I'm surprised the test has not been done or offered as an option.
I did the patch/Quadrafilar testing years ago with a handheld patch antenna mapping GPS and a Quadrafilar one. Both units had signal strength meters that gave the incoming signal strength. Outdoors both worked fine. The Quadrafilar one showed better signal strength and better limit of error circle than the patch one but both were fine for outdoor hiking.

The Quadrafilar was better at hiking in woods and would get a fix from my all-seasons room whereas the patch could not. Either type used as a launch base GPS is fine for rocket tracking as we're outdoors on an open range. The Garmin 60Cs and CsX can be plugged into a D72A or D74A and have a "map-in-the-hand" for APRS (like Beeline or Byonics) rocket tracking. That's great because it can show one obstructions one has to maneuver around to reach the final lie of the rocket.

On Yagi antennas. The beamwidth on the 2 meter (144Mhz) and 70cm (400Mhz) bands are sufficiently wide enough to be able to hold the downlink in flight by pointing the Yagi roughly in the direction of the rocket. On 900Mhz I've been told that the beamwidth of a 33cm (900Mhz) something like 8 element Yagi is too narrow to be able to point reliably at a rocket in flight. I don't know as I've never tried to test it in that fashion. I did read where a person used a large Yagi on 900Mhz to track a rocket in flight but I don't know how aggressive a flight it was.

I've used the stock antennas on 900Mhz trackers for inflight tracking and then switch to a 900Mhz Yagi after the rocket is down. A 900Mhz Yagi does definitely increase the ground footprint with the rocket on the ground. Heck, it's not moving that fast anymore so easy to point at! Would be helpful with a far ranging flight with a 100mW, 900Mhz tracker.

This is an example of a 900Mhz patch antenna: eBay (ebaydesc.com) If flying very aggressively with a low powered 900Mhz tracker, holding the patch antenna in the general direction of the in-flight rocket allows the best reception and recovery of the NMEA sentences. I've achieved the best decoding of the position data even on flights that are not that aggressive. I drop the patch when the rocket is down and switch to a Yagi. I have mine mounted on a 12 foot fiberglass pole that incidentally was a Shakespeare outdoor antenna for the very early cordless phones on 47Mhz. I used it in 1979 for that purpose. Was fun to take and make phone calls 3 blocks from my apartment. (That was before cellphones mind you.) Now it's repurposed to hold my 900Mhz patch antenna.

Once one GPS tracks a rocket, they'll be hooked walking right up to their rocket. Especially if the flight is totally "sight unseen". I've seen folks demeanor sink tremendously when they overpowered their rocket and it was a totally sight unseen flight. If there was no onboard tracker, good luck finding it unless it's a large launch and someone else lucks upon the downed rocket. If RDF was used one has to start cruising around and see if they get lucky to pick up a signal on the downed rocket. Again, if it's a totally sight unseen flight, it can be a crapshoot for one to stumble into the ground footprint of the RDF tracker. Even a glimpse of an RDF rocket coming in under main, even at a distance can help immensely with RDF recovery. One can get a general direction to travel and are very likely going to get within the ground footprint of the RDF tracker. If in vegetation, they'll find it.

As an aside, a ground mapping GPS that has a "Sight 'n Go" feature can help immensely. Some Garmin models have it. One sights the rocket along an axis on the GPS as it is getting close to the horizon, push a button and the GPS locks a bearing arrow on that direction. Great if one has to go around obstacles. I've used it alone with model rockets that were lost in tall grass! I sight the rocket just before it touches down and walk the line. Sometimes I'm surprised how far I have to walk but I've never lost a modroc using sight n' go. In tall grass, the parachute usually stays on top of the grass with the rest of the rocket underneath. Makes it easier to find. Even if one is never going to do Rf or GPS tracking. A sight 'n go capable mapping GPS is good insurance to maximize recovery of model rockets that land in deep grass or a distance away. Just shoot the line and keep walking. (As long as it's not a totally sight unseen flight mind you.)

With GPS, one has a readout of where the rocket is. Doesn't matter if the winds aloft cause the rocket to drift under drogue 180 degrees opposite of the ground wind direction. That can really confuse people if they are trying to get a visual. GPS tracking can cue where to look to attempt a visual on descent.
I've tracked other people's rockets and witness the 180 degree switch on the mapping program in realtime. Folks are looking the wrong way to try to get a visual on the rocket and I have to yell and point, "Look this way, it switched direction." That is always nice to have if the descent can be seen. If the rocket lands in vegetation, if there is a noisemaker on the harness even if the flight was totally sight unseen, the flier is going to get their rocket back as the GPS will get them up close. The last known position with the rocket in the air just before touchdown is more than likely going to get one within the ground footprint of the tracker for the final lie if the rocket isn't within sight.

GPS tracking even assists with core samples. I had one with a small fiberglass single deploy rocket. Put too much grease on an O ring and some blocked the "blow hole" for the 4F ejection charge. Went totally sight unseen and received one position downrange. I walked out there and there was just the fincan sticking up.

Dug it out, new nosecone, new Eggfinder and good to go. Got the Eggfinder on holiday sale so I think I only lost like $50.00. That was easier to swallow and I got the rocket and the motor casing back. Better than losing the$234.00 Beeline GPS I had on a apogee only, no drogue flight where the drogue didn't blow.
Main chute had a high speed deployment and the harness broke. Interestingly the chute was recovered and didn't show any signs of stress! Got my cataracts fixed shortly thereafter as I missed putting in one leg of the ematch on the drogue. The altimeter I used (an early model Raven) beeped continuity the same if one ematch or two ematches had continuity. Which means it beeped the same with one proper ematch connection and if the second ematch didn't have continuity, it still beeped the same.

Most altimeters have beep patterns that indicate continuity on both channels and if one channel has no continuity, the beep pattern will cue the flier there is a problem and which channel it's on.

I believe later Ravens had this issue corrected.

As mentioned once one tries GPS tracking, they'll be hooked once they have their first totally sight unseen or recovery from deep vegetation flight.

Kurt Savegnago

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#### ghuber

##### Greg Huber
I used an Eggfinder Mini setup on my L3 flight, but I've also experimented with a homebrew Ardunio-based 915mhz system that seems to work reliably over reasonable distances. A public github page, including code, parts lists, and documentation is here: https://github.com/gregoryhuber/GPSRocketTracker. It includes a feature to walk you to your rocket (Rocket is this distance away on that bearing) and also displays Lat/Long/Alt of rocket, so you can just type it into google maps/something else.

As is the case with the Eggfinder, the key issue is that once the rocket is on the ground, the GPS may not be able to "see" the sky, and so you get the last location that the unit picked up. Additionally, radio range is much lower once the unit is laying flat on the ground. That said, at URRF 7.5 this year we were able to locate a 29mm rocket from 1.2km away, over flat ground.

In the long term, I'd like to add bluetooth functionality to the base unit (so it broadcasts the Lat/Long to a phone directly) and logging to both the base unit and tracker, but those would up the cost and complexity. As it is now, if I lose the transmitter unit it is $80 out the door (less if you use a different GPS unit). #### RocketScientistAustralia ##### Well-Known Member #### Mike Haberer ##### Well-Known Member TRF Supporter The cheapest Eggfinder system is about$100. So if you got everything for free the most you can save is $100. That's how I tend to look at things - what's the most I can save? Your main question is: "Can a functional, durable homebrew tracker be made for substantially less money than it can be purchased?" Based on my criteria, I would say no - saving$100 to try and duplicate something that is readily available from a vendor with known excellent support is not worth the effort, if saving money is the main goal.

But in the end it's a decision only you can make, based on your goals for such a system.

Tony
But...but...but...since I was new to the whole soldering thing, it took three tries to get an Eggfinder Mini that works (the first one was definitiely borked, I'm still scratching my head on the 2nd one since it looks good), so I probably could have bought a Missileworks T3 for what I spent on the Eggfinder. Then again, I'm pretty good at soldering now. It is a hobby, after all....