Eggfinder range - ground test and launch results

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Dad Man Walking

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There has been a bit of tooth-gnashing on some other threads about the degradation of the Eggfinder RF signal when the transmitting antenna is positioned near a metal object such the central threaded rod in some nosecone setups. So we decided to test a couple of different setups to see what the fuss was all about.

We set up the Tx board with a rubber antenna about six inches long (something like 2-4db gain, if I recall), and a similar antenna on the Rx module. Our test range was along the RR tracks running through town, where we had line-of-site across the ground. We shoved the NC with the Rx module inside into a bush about 4-5' off of the gound, and started walking. These are obviously not optimal conditions for the 900Mhz radios, but we were not interested in maximum range in real launch conditions, just the difference between the signal with the antenna next to the threaded rod vs. being on the opposite side of the bulkhead.

With the antenna installed inside the NC, parallel to the threaded rod (around 1" away) we got signal for up to 1/2 mile over the ground. Over the second half of that distance we started to get signal loss at the receiver but we would reacquire fix after a few seconds. At the 1/2 mile point we could no longer acquire a signal. We then repositioned the Tx board/antenna so it was on the opposite side of the bulkhead, opposing the threaded rod. In this configuration, we got out to 0.6 miles before the signal dropped out entirely. So according to my my hillbilly engineering, I'm a-figurin' that there's potentially a 20% degradation in signal strength when the antenna is sharing space in the nose cone with a steel threaded rod.

The ground tests do not represent the performance of the system in clear air. This weekend we flew the same set-up - same Tx and Rx antennas, with the Tx antenna mounted opposing the threaded rod, outside of the nose cone. Flight was to 14,000 feet, Mach 1.5+. Two Rx units tracking, both lost fix only once, at the same time and only for about a couple of seconds during the "up" phase, not sure if that was during boost or coast. Both Rx units locked through the rest of the flight.

Impressive little piece of kit! Thanks for making this possible for us, Cris.
 
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I'm using a similar setup with the rubber duckie antenna on both my RX and TX Eggfinders. Flew them three times at Airfest to over 10,000 ft. with about the same results. I think the GPS module looses lock during boost, but recovers quickly.
 
I'm using a similar setup with the rubber duckie antenna on both my RX and TX Eggfinders. Flew them three times at Airfest to over 10,000 ft. with about the same results. I think the GPS module looses lock during boost, but recovers quickly.

Just found this page with a ton of great information about GPS modules, antennas, and stuff like that. Might even be digestible by an ol' hillbilly. In Ken Biba's article (link here to John Coker's page, scroll about 1/3 down for Ken's article) he explains that the GPS modules that work for rocketry can keep lock at higher speeds than ones used for tracking cars, people, dogs, etc., and because of this they may stop outputting when a preset speed is exceeded, and then start again when things slow down. This is done in deference to the feds here and abroad. The threshold noted for one popular GPS module is 515 meters/second, which our flight exceeded for a short time.

Makes me wonder if losing lock is a "feature" and should only be happening on flights that are exceeding a preset limit. (515 meters/second is roughly Mach 1.5 at sea level--pretty darn fast).

Ken's article also gave an example where a "slow moving object" chip didn't just lose lock, it gave widely inaccurate readings when used in a rocket. If we are not seeing this then I'm assuming that Cris delivered the goods on the GPS module.
 
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I got 14911' @M1.6 with just the wire Tx antenna. I didn't see if I lost lock, but probably did. I was too busy watching the flight up until I saw the smoke from the apogee event and then lost sight of the rocket. Checked Rocket Locator and it was tracking it fine. Drove straight to it 2.4kms away. I'll be putting the same rocket over 16k' next March, and hoping to do a 54mm MD to ~25k' at the same launch. I'll be using an EF in it. Fantastic product.
 
I'm putting one in my carbon fiber Mongoose 75, but I will probably use the rubber duckie antenna in it too, there is room in the 3" N/C. Same setup as in my 3" Darkstar, but with the 75mm MMT, I should be able to punch through 20,000 ft. I still don't think we have found the max altitude these Eggfinders will work to, but I'm all for trying to find out.
Thanks for the great thread!

Hey Dad, can you post a link to Ken Biba's article?
 
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I'm putting one in my carbon fiber Mongoose 75, but I will probably use the rubber duckie antenna in it too, there is room in the 3" N/C. Same setup as in my 3" Darkstar, but with the 75mm MMT, I should be able to punch through 20,000 ft. I still don't think we have found the max altitude these Eggfinders will work to, but I'm all for trying to find out.
Thanks for the great thread!

Hey Dad, can you post a link to Ken Biba's article?

Is the NC CF in the Mongoose? I do beg to differ on ground testing. Sure, free air performance is certainly much greater but if one's ground range is
markedly attenuated, there's a problem that should be looked at before flying. I had good range at 300 feet with a 70cm APRS tracker but failed to get
any usable packets from 3500' and 10,000'. Was the paint that attenuated the Rf. Kurt
 
Is the NC CF in the Mongoose? I do beg to differ on ground testing. Sure, free air performance is certainly much greater but if one's ground range is
markedly attenuated, there's a problem that should be looked at before flying. I had good range at 300 feet with a 70cm APRS tracker but failed to get
any usable packets from 3500' and 10,000'. Was the paint that attenuated the Rf. Kurt

I Think the NC is filament wound finerglass died black.
 
(Snip for Brevity's sake)

With the antenna installed inside the NC, parallel to the threaded rod (around 1" away) we got signal for up to 1/2 mile over the ground. Over the second half of that distance we started to get signal loss at the receiver but we would reacquire fix after a few seconds. At the 1/2 mile point we could no longer acquire a signal. We then repositioned the Tx board/antenna so it was on the opposite side of the bulkhead, opposing the threaded rod. In this configuration, we got out to 0.6 miles before the signal dropped out entirely. So according to my my hillbilly engineering, I'm a-figurin' that there's potentially a 20% degradation in signal strength when the antenna is sharing space in the nose cone with a steel threaded rod.

The ground tests do not represent the performance of the system in clear air. This weekend we flew the same set-up - same Tx and Rx antennas, with the Tx antenna mounted opposing the threaded rod, outside of the nose cone. Flight was to 14,000 feet, Mach 1.5+. Two Rx units tracking, both lost fix only once, at the same time and only for about a couple of seconds during the "up" phase, not sure if that was during boost or coast. Both Rx units locked through the rest of the flight.

Impressive little piece of kit! Thanks for making this possible for us, Cris.

One thing the would make this more enlightening would be what the range was in the bush with the antenna in the open without metal interference? The significance would be more glaring if the range was 1 mile or more in free space. The thickness and length of the rod can make a difference and the degradation could end up more than 20%.
The bottom line is if range is utmost and necessary, avoid the metal interference. But yes you may get away with it.
Link to John Cokers article on GPS: https://www.jcrocket.com/gps-tracking.shtml
At the top there is a link to an article by Ken Biba. I don't know if this is the same one. Kurt
 
No problemo with an NC tracker then. I'm beginning to favor the tube/carrier through the bulkhead approach with or without an offset eyebolt depending
on the nosecone diameter. Kurt

That's what I've concluded as well. I posted a couple of solutions I came up with on the Eggfinder Bay thread. You know, the one where you were thinking to hard and not flying enough... :)
 
One thing the would make this more enlightening would be what the range was in the bush with the antenna in the open without metal interference? The significance would be more glaring if the range was 1 mile or more in free space.

If it wasn't clear in the original post, the 1/2 mile range was with the antenna in the nose cone, next to the threaded rod. The 6/10ths of a mile range was when we positioned the antenna outside of the nose cone, on the opposite side of the bulkhead, so it was in the open. Is this what you were suggesting?
 
If it wasn't clear in the original post, the 1/2 mile range was with the antenna in the nose cone, next to the threaded rod. The 6/10ths of a mile range was when we positioned the antenna outside of the nose cone, on the opposite side of the bulkhead, so it was in the open. Is this what you were suggesting?[/QUOT

OK, that isn't much loss then. I had 1/2 mile range in a crowded city environment with the EF antenna in freespace and didn't have time to go any farther. Was using a mag mount antenna on top of an SUV and still received good position packets.

One can look at the issue of parallel metal rods like the elements of a Yagi antenna.
The element sizes are chosen for signal gain, directivity and or bandwidth. If the elements are not sized accordingly the antenna may not perform.
On the other hand, by chance interfering rod(s) might not have as much of a negative effect on the performance. This would vary from installation to
installation. It didn't hurt your range much with the given transmit and receive antennas. Cris has the no metal advice in the instructions and also besides
John Coker's article mentioned above, there is some useful information in the instructions for the Altus Metrum products. I think it's great that flyers are
seeing great reception with the EF system. I'm wondering how far that could be extended with a patch antenna ultimately. Kurt
 
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I suppose if the elements of the allthreads were just the right length and you positioned the antenna just the right way, it might act as a Yagi. This may not be a good thing, though, you want the transmitter's antenna to be omnidirectional because you may not know which way it ends up pointing or exactly where it might be.
 
I Think the NC is filament wound finerglass died black.

Was looking at the website on the Mongoose and it says: ProFusion Graphite 5:1 Von Karman Composite Nosecone. If that's the case one might have to come up with an external antenna if they want to track at extreme altitude. Only sure thing I could figure is place the EF in a shock resistant carrier and attach it to the
sustainer shockcord to be deployed at apogee. A rear facing bulkhead SMA antenna mount might be an alternative for an Egg Finder riding in the Ebay with the deployment electronics. Would need to be certain the Egg Finder doesn't interfere with the deployment electronics in that case plus would have to test to see
if the GPS could get a lock from inside the carbon fiber tubing. If the GPS can't get a lock inside of the carbon fiber environment, riding the apogee/sustainer shockcord would be the only viable tracking possibility. If one took the trouble to replace that terribly nice graphite nosecone that would be a work around.
Will be interest to see what Wayne reports how he gets around this. Of course could just toss an RDF tracker on the shockcord and do it the old fashioned way. Kurt
 
"Profusion graphite" is the same black fiberglass that Wildman uses in his kits, which I have flown with Eggfinders in both my 3" Blackstar, 54mm blackhawk and "Jughead". I will probably use the same sled/Nosecone setup in the Mongoose. The only difference in the Mongoose setup is that it has a carbon fiber bulkhead and coupler, and I might just replace it with a fiberglass one, or not, I no longer run the antenna out the bottom, there is plenty of room in the nosecone.
 
"Profusion graphite" is the same black fiberglass that Wildman uses in his kits, which I have flown with Eggfinders in both my 3" Blackstar, 54mm blackhawk and "Jughead". I will probably use the same sled/Nosecone setup in the Mongoose. The only difference in the Mongoose setup is that it has a carbon fiber bulkhead and coupler, and I might just replace it with a fiberglass one, or not, I no longer run the antenna out the bottom, there is plenty of room in the nosecone.

If it's simply fiberglass nosecone should not be radio opaque then. If you have it riding upright a CF bulkhead shouldn't be a problem. Kurt
 
"Profusion graphite" is the same black fiberglass that Wildman uses in his kits, which I have flown with Eggfinders in both my 3" Blackstar, 54mm blackhawk and "Jughead". I will probably use the same sled/Nosecone setup in the Mongoose. The only difference in the Mongoose setup is that it has a carbon fiber bulkhead and coupler, and I might just replace it with a fiberglass one, or not, I no longer run the antenna out the bottom, there is plenty of room in the nosecone.

One other point (for those who haven't seen my last post on the Eggtimer AV Bay thread)...I ended up ditching the central rod/glueless coupler design and cemented the coupler in place, attached the metal tip with a short bolt like it came with, and used an interior bulkhead. Less flexibility for future mods, but the stuff I'm doing with it now is much easier, and we don't have to worry about an antenna dangling through the bulkhead/protruding into the payload section. That seems create some other problems--sealing the hole in the AV bay, and protecting the antenna from shocks that could damage the connector on the board. For the 14K flight, the rocket (not mine) had the central rod, the circuit board was inside the NC, and the antenna was poking through into the payload tube. To protect the antenna, a 1/2" wooden dowel had been cemented to the outside of the bulkhead right next to the antenna, and cable ties were used to secure the antenna and provide some protection to the exposed antenna.

On the Eggtimer bay thread, I will add a description of a third approach I am part-way through. It is a freestanding bay that will hang from the recovery harness. Haven't finished it yet so not ready for pics.
 
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