GPS Altimeter OK in black payload?

[billdz]

I vaguely recall seeing an article saying that a GPS altimeter should not be placed into a black-painted payload or nose cone, because it blocks the signal. Is that correct? I've been a ham for 40 years and have never heard of signal strength being affected by color.

 

[new2hpr]

No, it shouldn't be placed in a conductive (graphite or carbon fiber) nosecone for the obvious signal blocking reasons. Black paint is not the issue.
-Ken

... Unless, of course, your black paint is black from a high carbon content...:wink:

 

[billdz]

OK thanks, that makes more sense.

 

[cerving]

Darn near all of my FG nose cones are black, never had a problem, including some with metal tips. You just can't use metallic paints or CF, they either block or scatter the RF.

 

[ksaves2]

Darn near all of my FG nose cones are black, never had a problem, including some with metal tips. You just can't use metallic paints or CF, they either block or scatter the RF.

Fellow reported a modest 1dB attenuation on 70cm I believe. I wished I had saved the thread link here. The attenuation is of course frequency dependent.
I flew a metallic painted rocket to 10k and received only one position at altitude. The metallic paint was translucent to the incoming GPS signal because
I was able to download a very valid .kml file off the Beeline GPS 70cm lower powered GPS tracker. If the Rf can't get out, not good. Kurt

 

[OverTheTop]

Fellow reported a modest 1dB attenuation on 70cm I believe.

That would be me, I think. The thread you are looking for is here:
https://forum.ausrocketry.com/viewtopic.php?f=32&t=5661

As I said in the thread, it is based on the unit I tested only, with a sample size of n=1.

If I get time I should throw the comb generator in the EMC chamber and do comparative scans with and without the NC as a hat. That will check all frequencies in one scan. I think the results will be remarkably similar, but the experiment needs to be done to confirm. Should be able to get to that sometime by mid-2018 if I am lucky

 

[bigredbee]

I'd be concerned about temperature w/ a black nosecone. I think it was Charlie W at Blackrock that was measuring temps inside a black nc in excess of 100C

 

[ksaves2]

That would be me, I think. The thread you are looking for is here:
https://forum.ausrocketry.com/viewtopic.php?f=32&t=5661

As I said in the thread, it is based on the unit I tested only, with a sample size of n=1.

If I get time I should throw the comb generator in the EMC chamber and do comparative scans with and without the NC as a hat. That will check all frequencies in one scan. I think the results will be remarkably similar, but the experiment needs to be done to confirm. Should be able to get to that sometime by mid-2018 if I am lucky

Thanks, The thing I was impressed with was your rather impressive and likely accurate setup. Yes N=1 here but if one is going to an extreme, might be a better
idea to use a more powerful (ie 100mW) tracker or with a nosecone tracker have an aft facing antenna into a radiolucent upper bay.

Of course, if one does a clear air ground test with a black nosecone mounted tracker and is satisfied with the range, that is reassuring they will have a good
prospect of tracking. I tell you, it's a very sick feeling if one launches a very pricey setup to sight unseen territory and no positions are received due to
a suboptimal setup. I don't want to repeat my experience of 10 years ago and just lucked out the rocket was seen under main at the limits of vision and
was recovered in an open field. The temperature concerns Greg reports above might be obviated somewhat by taking the trouble of painting the
cone with a brighter, non-metallic paint. Kurt

 

[Gregory R]

I'd be concerned about temperature w/ a black nosecone. I think it was Charlie W at Blackrock that was measuring temps inside a black nc in excess of 100C

I also had an issue with high temperature inside a black fiberglass nosecone at Blackrock. The transmitted packets were not decipherable. I think it was explained that the transmitted frequency tends to drift as the temperature gets too high.

 

[OverTheTop]

Thanks, The thing I was impressed with was your rather impressive and likely accurate setup.

No worries. Our lab is not NATA certified but the system is benchmarked against a NATA lab. Chamber is 5m long, and is used for both immunity and emissions testing. It is very well maintained and used extensively during product development and compliance certifications.

Its nice to have access to fancy equipment


Note comb generator in foreground, and 435MHz patch antenna under test.