Rocketry Trackers 101?

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Spurkey

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Are there any good articles that explain all the myriad of options for trackers and what the pros & cons of the different types are? There are many many threads on here but the bulk are written by people much smarter than I who already know what they're doing. I was hoping to find a "Trackers For Dummies" book/article/webpage to help me climb the first bit of the learning curve. Here's what I know so far:

Transmitter
This is the bit that goes into the rocket. Some of them are GPS-based and output some kind of special stream, some are radio-based. Some of the radio-based ones require a ham radio license to be able to use, I haven't quite figured out how to tell which is which. I'm in Canada so I'm not sure if the licensing rules are different here. GPS is obviously much more precise since it can tell you more accurately where the rocket is, what're the downsides to it? Why would someone still go with a radio-based one? What does a ham-radio-based variant provide over a 'regular'-radio one?

Receiver
This is the bit that you hold in your hand to find the other bit that went into the rocket. Some people are able to use their phone/laptop, some people are able to use their phone/laptop only when it's hooked up to another thing, some people need a whole separate thing. I'm guessing some of these things are only usable if you also have the ham radio license. There also appears to be some discussion about which antenna to use with which receiver which adds another layer to the discussion. What pros & cons exist for the various receiver types?

My descriptions are overly simplistic because I don't quite have a handle on all the terminology yet. Any additional information would be greatly appreciated.
 
That article is absolutely fantastic, that's exactly what I was looking for! I shoulda known to check your site, I've used it as a reference a few times in the past...:facepalm: I've read through much of that article, and will probably need to read through it a few more times to absorb all the great info in it, but I still have a few questions.

https://jcrocket.com/gps-tracking.shtml said:
...which can be a cheap HAM handheld with an external APRS TNC or it can be a more capable radio with a built-in TNC
I found what APRS was in the references section but what is TNC?

https://jcrocket.com/gps-tracking.shtml said:
The worst antenna location is between and in-line with threaded rod and near flight computers. Long steel rods (>80% of a half-wavelength) will have a significant attenuation affect.
Is there a way of measuring the attenuation effect? I assume doing so would require additional specialized equipment, I ask more out of curiosity than anything. It would be nice to know if a given transmitter's placement in a rocket is affecting the transmit signal, especially if I don't know what I'm doing at the start. :)

The 'Product Comparison' table was great, any recommendations for comparing other trackers not listed? For example I was looking at these 2:
https://www.eggtimerrocketry.com/page21.php
https://www.tragiclittleaerospace.com/
And wanted to know why one was $90 and the other was $300. A lot of people seem to really like the u-blox stuff so I'm assuming it's a better chip but is it 3x better? I'm not trying to put the other one down, I'm just trying to figure out which might be better for what I want to do.
 
I found what APRS was in the references section but what is TNC?
A Terminal Node Controller is used to translate audio signals into digital packets.

Is there a way of measuring the attenuation effect?
I'm sure there is, but I'm not an expert. (The antenna section was written by Grant Saviers.)

The 'Product Comparison' table was great, any recommendations for comparing other trackers not listed?
I have not had experience with those two, but you might try to take a shot at filling out the table for them.

It's really hard to boil down the comparison to a simple table because what is most important (and drives the decision) varies. For example, some people think getting a HAM license is too difficult and their choices will be driven by that.
 
I have not had experience with those two, but you might try to take a shot at filling out the table for them.
Challenge accepted. :)

It's really hard to boil down the comparison to a simple table because what is most important (and drives the decision) varies.
Agreed, information invariably gets left out. I still think your table is a good start though as it can help quickly eliminate certain choices to narrow the problem domain. It's nice to have data from the different options in a consistent format & consistent units which serves as a starting point for comparing potential new entries.
 
Basically, is one trying for a record attempt under TRA rules? https://www.tripoli.org/LinkClick.aspx?fileticket=qM5Rub0u6jM=&tabid=344
Those are the choices above for above 30'k.

Everybody else.

Precision tracking: GPS based which transmits positions from GPS receiver. Two choices here- Ham Radio APRS (Automatic Packet Reporting System) and
Unlicensed 33cm (900Mhz) band of which there are several rocketry intended devices and converted Garmin dog trackers.

Non-Directional Beacons with Yagi antennas and attenuators. Was the only game in town for years. Gave direction/bearing but not distance. Walston, Rocket Hunter, Com-Spec.

John Coker's article is an excellent overview.

For precision tracking, Ham Radio APRS is an option. The equipment was financially competitive with the commercial non-directional trackers but one had to get a Ham license. 900 Mhz devices followed but were rather pricey and generally cost as much or a bit more as the available Ham equipment of the time.

The EggFinder kits hit the market 6 months or so ago with an affordable price point but have to be assembled. Not acceptable for altitude records but intended to assist sport fliers. Price is very attractive. Combination deployment altimeter and GPS tracker (TRS) released about a month ago. One doesn't have to worry about the Rf tracker interfering with the deployment device due to opto-isolation. Big problem with Garmin Dog trackers mounted in proximity with deployment devices.

Kurt
 
Is there a way of measuring the attenuation effect? I assume doing so would require additional specialized equipment, I ask more out of curiosity than anything. It would be nice to know if a given transmitter's placement in a rocket is affecting the transmit signal, especially if I don't know what I'm doing at the start. :)

Yes. To do so generally requires somewhat specialized, but expensive, equipment known as a spectrum analyzer. In the specific case of your chosen transmitter, some receivers include a signal strength indicator.

Overall, however, the location in the rocket is going to to little that altitude, velocity, and orientation won't do ten times over. If your system is usable when assembled in your workshop, that is probably enough. The only real considerations should be choosing a RF-transparent construction material, and keeping the orientation of the two antennas the same (this will probably mean fitting the transmitter however it does so best in the rocket, and matching that orientation with your receiving antenna.
 
Yes. To do so generally requires somewhat specialized, but expensive, equipment known as a spectrum analyzer. In the specific case of your chosen transmitter, some receivers include a signal strength indicator.

Overall, however, the location in the rocket is going to to little that altitude, velocity, and orientation won't do ten times over. If your system is usable when assembled in your workshop, that is probably enough. The only real considerations should be choosing a RF-transparent construction material, and keeping the orientation of the two antennas the same (this will probably mean fitting the transmitter however it does so best in the rocket, and matching that orientation with your receiving antenna.

Simple Rules:

1. Stay away from carbon fiber airframes if one is considering burying the tracker antenna inside the rocket. There is a way around this by bulkhead mounting an antenna that gets exposed with drogue deployment or putting the tracker on the shockcord deployed at apogee. Some have resorted to copper foil strip on the surface of the airframe but if going really extreme speeds with airframe heating, that could cook off.

2. Stay away from metallic paints with the rocket body parts that surround the antenna. If one has the antenna projecting into the main parachute bay, it should be a non-metallic paint. Sure the sustainer and the nosecone can be metallic since they are not directly shielding
the antenna but the bay containing the antenna needs to be non-metallic ("glittery") paint. The degree of shielding is dependent on the transmitting frequency and the metallic particle size in the paint. Example: Rattle can Dutch Boy metallic paint will effectively shield a low powered Beeline GPS at altitude at the 70cm band (420-450Mhz) but the GPS receiver will still get a lock on the satellites. How is that?
The paint doesn't shield the incoming satellite signal because a perfectly valid position log was downloaded after a flight with no packets received via RF at altitude. (The Beeline GPS has onboard memory to record positions at a higher rate that can be downloaded after recovery. Positions are transmitted via the APRS protocol once every 5 seconds.) To avoid any problems, don't use metallics on an airframe unless you plan an external antenna system.

3. High power is not necessarily better. You can't effectively carry enough battery power for a high-powered tracker that will give you
a position packet in a depression 5 miles away. It simply isn't necessary plus high Rf fields can shut down deployment electronics.
What's high power? 50 to 100mW on up based on my being burned and witnessing others having less than nominal flights with high powered trackers. Dog trackers are notorious. Stock low powered Beelines ride next to most altimeters with no issues. Ask around to people who
track and see what they say about known problematic altimeters. Also see Mike Konshak's article and scroll down to page 15-16 for more information: https://www.apogeerockets.com/downloads/PDFs/GPS_Recovery.pdf
Yeah, yeah, yeah. I know folks fly the 50 mW NDB (non-directional beacons) on the sustainer/apogee shockcord but
I would still use caution if sticking a 50mW tracker right next to an "untested" deployment device.

4. Test, test, test. It goes without saying, test, test, test. Try and hoist your ebay 10 feet into the air and take a walk. If you're getting a good signal at over a mile, you're in good shape. If there are a bunch of obstructions in your test area and you're 1/2 mile you're probably still in a good position. You got an open area you can test in and even put your ebay a few feet off the ground on a chair or step stool, even a better place to test. Second, put the rocket together, bare ematches in canisters, turn on the altimeter(s) and then turn on the tracker and let the rocket stand there for 30 to 60 minutes. Yes, 30 to 60 minutes. If the ematches don't pop or you don't hear an altimeter reboot or shutdown, you are in a good position for success. A good time to do this is let the rocket "test away" while you are doing some building work in your shop. Turn down the radio/stereo and keep an "ear open" for the altimeter(s) beeping or not.

If I would have known about the above before I started using Rf to track, it would have saved me a lot of grief. Also observing others was a very useful learning experience. A GPS tracker is more likely going to get a flier to their rocket and get it recovered faster than a non-directional beacon (ie. Rocket Tracker, Walston)
If a person enjoys the sport of radio tracking by bearing alone then more power to them. Some folks are very good at it. If one's flying time is limited by life, weather and/or geography, recovering a project as expediently as possible allows them to go on to fly other projects.

I discovered the hard way that launching a high flying rocket at the beginning of a launch could led to wasting most of one's time trying to recover it if no means of Rf tracking was provided. That meant that several rockets went unflown at a given launch. I prefer the mantra, "Git 'r done, git'r flown and git' em back!" ASAP. Kurt
 
For me, both location and environment were key in my rockets for reliable tracking. Flying the Altus Metrum TeleGps v 1.0, I initially was NOT maintaining a good gps lock or a reliable downlink signal. First, I abandoned the idea of keeping it in the Av-bay and moved the TeleGps to the nose cone (I use a magnet switch so that I don't have to drill any holes in the NC.). The coverage improved with that move, but still it had many holes in the data coming via the downlink. Next, I replaced the steel 1/4 x 20 all-thread with a nylon 1/4 x 20 all-thread. Everything fell into place at this point; I had much improved signal strength and a much more complete data track via the downlink. I've now flown to 18,112 feet with very few holes in the data via the downlink. That one landed 1.95 miles from the pad.


Yes. To do so generally requires somewhat specialized, but expensive, equipment known as a spectrum analyzer. In the specific case of your chosen transmitter, some receivers include a signal strength indicator.

Overall, however, the location in the rocket is going to to little that altitude, velocity, and orientation won't do ten times over. If your system is usable when assembled in your workshop, that is probably enough. The only real considerations should be choosing a RF-transparent construction material, and keeping the orientation of the two antennas the same (this will probably mean fitting the transmitter however it does so best in the rocket, and matching that orientation with your receiving antenna.
 
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Next, I replaced the steel 1/4 x 20 all-thread with a nylon 1/4 x 20 all-thread. Everything fell into place at this point; I had much improved signal strength and a much more complete data track via the downlink. I've now flown to 18,112 feet with very few holes in the data via the downlink. That one landed 1.95 miles from the pad.[/QUOTE]

Several times on TRF i have seen people say that the nylon will not be strong enough for rockets. Can you elaborate of your AV bay and size of Rocket?
 
Here's some real numbers. https://secure.microplastics.com/mechanicaldata.aspx

It appears that a single 1/4-20 thread can take a 75 pound load with a factor of 4 design factor or a 150 pound load with a factor of 2 design factor (on yield).

If you are clever in your design, you can design an e-bay where the only load on the threaded rod is the weight of the rod and the altimeter.......

Bob
 
Here's some real numbers. https://secure.microplastics.com/mechanicaldata.aspx

It appears that a single 1/4-20 thread can take a 75 pound load with a factor of 4 design factor or a 150 pound load with a factor of 2 design factor (on yield).

If you are clever in your design, you can design an e-bay where the only load on the threaded rod is the weight of the rod and the altimeter.......

Bob

Thanks Bob, that sounds like the type of e-bay that has the "pass" through one piece shock cord so no load is really on the e-bay. Is this correct?
 
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