GPS Tracking Effectiveness in Electronics Bay vs. Nose Cone

[tsbooska]

Hello all! I am in the process of designing the first rockets that I'd like to use head-end deployment on, similar to the Wildman Punisher and other similar rockets. With this setup, I find it likely that the GPS tracker I'm using, the Featherweight tracker, will have to be in the avionics bay, along with two all threads and eyebolts, rather than in the nose cone. Both rockets, at the time of writing, are projected to go M1.2-1.5 and ~14,000 feet.

What has been all of your experiences with the discrepancies between the effectiveness of putting the tracker in the electronics bay versus the nose cone? I understand that the steel in the electronics bay will have an effect on the effectiveness of the tracking, but in your experience, is this a difference that is too small to notice or monumental? Should I take extra measures to place the tracker on the shock cord or in a small compartment at the top of the nose cone?

Thank you all for your help,
Thomas

 

[mikec]

I'm sure there will be many opinions expressed. My opinion is that it'll be OK and the impact of the all-thread is minimal. But I don't have hard data; in my Punisher I have the GPS tracker in the bay, but I use the G10 sled as a structural element and don't have any all-thread. Certainly the aluminum bulkheads and eyebolts haven't degraded the signal appreciably that I have observed.

 

[pugachu]

I'm a ham operator, and have read several books on antenna designs etc. It all boils down to 'test it out'. Turn on your transmitter in it's intended position in the rocket with the hatch on, drive a few miles away with your receiver and see if you get a signal.

I do that on all untested designs. metal can act as parasitic antennas and either boost or attenuate the signal. it also can change the direction that the signal propagates.

 

[Art Upton]

Hello all! I am in the process of designing the first rockets that I'd like to use head-end deployment on, similar to the Wildman Punisher and other similar rockets. With this setup, I find it likely that the GPS tracker I'm using, the Featherweight tracker, will have to be in the avionics bay, along with two all threads and eyebolts, rather than in the nose cone. Both rockets, at the time of writing, are projected to go M1.2-1.5 and ~14,000 feet.

What has been all of your experiences with the discrepancies between the effectiveness of putting the tracker in the electronics bay versus the nose cone? I understand that the steel in the electronics bay will have an effect on the effectiveness of the tracking, but in your experience, is this a difference that is too small to notice or monumental? Should I take extra measures to place the tracker on the shock cord or in a small compartment at the top of the nose cone?

Thank you all for your help,
Thomas

Nose Cone, Fiberglass not Carbon Fiber I proved blocked signals

 

[Hobie1dog]

Nose Cone, Fiberglass not Carbon Fiber I proved blocked signals

I'll never forget this statement, especially coming from a fellow ham operator.

 

[Buckeye]

Hello all! I am in the process of designing the first rockets that I'd like to use head-end deployment on, similar to the Wildman Punisher and other similar rockets. With this setup, I find it likely that the GPS tracker I'm using, the Featherweight tracker, will have to be in the avionics bay, along with two all threads and eyebolts, rather than in the nose cone. Both rockets, at the time of writing, are projected to go M1.2-1.5 and ~14,000 feet.

What has been all of your experiences with the discrepancies between the effectiveness of putting the tracker in the electronics bay versus the nose cone? I understand that the steel in the electronics bay will have an effect on the effectiveness of the tracking, but in your experience, is this a difference that is too small to notice or monumental? Should I take extra measures to place the tracker on the shock cord or in a small compartment at the top of the nose cone?

Thank you all for your help,
Thomas

I have a head-end WM Mach2 with FW tracker and altimeter in the fiberglass av-bay. I had the same concerns, did some some ground testing, and found that the metal (aluminum in this case) all-thread made little difference to the GPS tracking.

https://www.rocketryforum.com/threads/wildman-mach2-hed-recovery-gear.165178/post-2167818
I did some testing on a BRB900 in another post several years ago. Same conclusion. I think this concern about metal affecting GPS is another one of those legends that propagates on the forum, like drag separation and redundant altimeters.

If you are really worried, then nylon all-thread is an option.

 

[jderimig]

Metal all-thread will change the radiation pattern. So what? Your rocket in flight and on its way down will most likely be in all possible orientations.

If the antenna is very close to the all-thread it may detune the antenna. So what? Its probably detuned already.

 

[OverTheTop]

I have a head-end WM Mach2 with FW tracker and altimeter in the fiberglass av-bay. I had the same concerns, did some some ground testing, and found that the metal (aluminum in this case) all-thread made little difference to the GPS tracking.

https://www.rocketryforum.com/threads/wildman-mach2-hed-recovery-gear.165178/post-2167818
I did some testing on a BRB900 in another post several years ago. Same conclusion. I think this concern about metal affecting GPS is another one of those legends that propagates on the forum, like drag separation and redundant altimeters.

If you are really worried, then nylon all-thread is an option.

Metal will affect antenna pattern and radiated power.

As long as you have sufficient link budget a reduction in emission will be of little consequence, so for all but the highest flights the tracking will probably be ok. Even if you lose packets near apogee you should get them again when altitude is lower.

Using nylon allthread is possible, but the tensile strength is greatly reduced compared to metal.

If you are really keen you can use titanium bike spokes. At 2mm diameter they have a breaking load of around 250kg. As a bonus their conductivity is much less than steel so will perturb the antenna field less. They are also good in electronics bays where space is restricted.

 

[mikec]

As a bonus their conductivity is much less than steel so will perturb the antenna field less.

The thermal conductivity of Ti is fairly low, but the electrical conductivity, while about 25x lower than copper, is not low enough to help much with this. Stainless steel has a lower conductivity than Ti according to https://www.thoughtco.com/table-of-electrical-resistivity-conductivity-608499

 

[OverTheTop]

Ok, but remember that the conductivity of Ti is less than steel, and its strength is much higher, so you need less of it. That gives another multiplier as there is less of it. Stainless suffers in the opposite direction.

Would need to run some EM simulations to verify either way.

 

[Art Upton]

Just Don't put the GPS in the Coupler Ebay, put it in the nose where it belongs like most all Sounding Rockets ... Just use plastic or Fiberglass, not Carbon Fiber Nose Cones that I have tested cause problems...

 

[user 30299]

This is one of my av-bays for a head-end deployment setup. It has the Missile Works T3 tracker and
4.7" dipole antenna mounted in the bay with a Stratologger and a Quark.

The threaded rods, u-bolts and nuts & washers are all steel. There's a mix of 9-volt and Lipo batteries.

The rocket is all fiberglass, a Composite Warehouse kit. This is NOT thin-walled fiberglass, so the tubing is very stout and heavy.

I've not had any issues with the GPS.

I have worked with Adrian's Featherweight (FW) in university team rockets in similar setups.
Never had any issues with so much stuff packed around the antenna. Now that I think
about it, I wonder if a more substantial antenna could be put on the FW transmitter?



Top Side of Sled & Bottom Side of Sled



Head-End Deployment Setup & Assembled Av-Bay

 

[Sailfish1957]

I think Adrian has stated that the all-thread and other electronics does not impair the FW GPS Tracker. I have no issues with my setup. This FW tracker is the newer one from Adrian; the Ublox SAM-MI-10Q